Prevalence of substance use and associated factors among secondary school adolescents in Kilimanjaro region, northern Tanzania.

BACKGROUND: Substance use among school-going adolescents increases the risk of developing mental disorders, addiction, and substance use disorders. These may lead to poor academic performance and reduced productivity, which affects adolescent lives. The study aimed to determine the prevalence of substance use and associated factors among secondary school adolescents in the Kilimanjaro region, northern Tanzania.
METHODOLOGY: The study used secondary data from a cross-sectional survey of adolescents aged 10-19 years from public secondary schools in the Kilimanjaro Region, northern Tanzania. Substance use was measured using the Global School Health Survey (GSHS) questionnaire. Categorical variables were summarized using frequencies and percentages, while numerical variables used mean and standard deviation. Multivariable logistic regression models were used to obtain odds ratios (OR) and 95% confidence intervals (CI) to determine risk factors associated with lifetime and current (within the past 30 days preceding the survey) substance use.
RESULTS: The lifetime and current prevalence of substance use among 3224 adolescents was 19.7% and 12.8%, respectively, while alcohol and cigarettes were commonly used. Female adolescents had lower odds of current substance use (OR = 0.63, 95%CI 0.50-0.80). Higher odds of current substance use were among adolescents who have ever had sex (OR = 4.31, 95%CI 3.25-5.71), ever engaged in a physical fight (OR = 2.19, 95%CI 1.73-2.78), ever been bullied (OR = 1.55, 95%CI 1.16-2.05), always seen alcohol advertisements (OR = 1.87, 95%CI 1.37-2.53), and adolescents whose parent/guardians rarely understood their problems (OR = 1.38, 95% CI = 1.03-1.85). Adolescents whose classmates always showed social support had lower odds of current substance use (AOR = 0.71, 95%CI 0.53-0.97). Similar factors were associated with lifetime substance users.
CONCLUSION: The study reflects a high prevalence of substance use among adolescents in the Kilimanjaro region. Alcohol and cigarette are the most prevalent substances used. Regulatory measures are essential to limit alcohol advertisements that are media portrayed. Efforts are needed to reduce risk behaviors, such as physical violence and bullying, through peer support groups/clubs in school environments.

Introduction

Substance use is the lifetime use of any substance, including khat (Catha edulis), cigarettes, illicit drug use, alcohol, and other substances [1, 2]. Substance use has increased in recent years and is a growing public health problem and a worldwide threat, significantly affecting young people aged 10–24 years [1-3]. The commonly used substances globally are alcohol, khat, cigarette, hashish, and other illicit drugs like cannabis, heroin, and cocaine [4, 5]. For instance, about 53% of people aged 15 years and above have ever used alcohol globally [6, 7]. A recent systematic review in sub-Saharan Africa estimated the prevalence of substance use among adolescents (10–19 years) to be 41.6%, with alcohol being the most prevalent (40.8%) compared to other substances [1, 2].

In Tanzania, the lifetime prevalence of substance use among school-going adolescents (11–17 years) was 7%, with alcohol at 4.5% and drugs (3.1%), specifically marijuana, amphetamines, or methamphetamines being the most used [8, 9]. In the Kilimanjaro region, cigarettes (15.5%), alcohol (9.2%), and marijuana (3%) were the most commonly used substances among school-going adolescents [10]. Studies on substance use and related risk behaviors among adolescents in Tanzania are scarce. Therefore, limited data is available to inform policy and interventions.

Adolescence marks a critical time of growth in the life course and profound changes in physical, cognitive, and social development [3]. Substance use at the early stages of adolescents increases the risk of developing addiction, mental disorders, and substance use disorders [1, 6]. For example, in developed countries, the estimated risk of developing drug dependence on cannabis uses alone among lifetime drug users who started using drugs during the adolescent period is 17% [11]. Substance use and mental disorders accounted for 183.9 million disability-adjusted life years (DALYs) in 2010, especially among adolescents and young to middle-aged adults aged 10–29 years [12-14]. In addition, substance use among school-going adolescents leads to poor academic performance, reduced productivity, high dropout rate, and indiscipline[4, 15], which have implications that can persist throughout the life course [16]. According to the Global initiative out-of-school children study in Tanzania, almost 2.3 million (57%) of secondary school-age children (14–17 years) are out of school; the reported dropout rate by 2014 among registered adolescents was 7.5% [17]. The factors are bad youth groups involved with substance use, specifically smoking bhang (marijuana) and truancy tendencies [17].

The Sustainable development Goals include strategies to reduce the burden of substance use among adolescents through strengthening the prevention and treatment of substance use [18]. Among other interventions, Tanzania’s adolescent health and development strategy 2018–2022 aims to ensure the availability of preventive and treatment services that are affordable, accessible, and friendly to reduce the burden of disease among adolescents. Also, the strategy recommends substance use counseling among adolescents, which would require promoting community-based youth centers and strengthening community involvement in the Adolescent Health Strategy (ADHS) to improve key adolescent health care practices [19]. Nevertheless, most existing interventions focus on sexual and reproductive health (SRH) and HIV/AIDS and less on emerging adolescent issues such as substance use, accidents and injuries, mental health, and road safety [19].

In addition, studies on adolescent risk behaviors in different settings focused on one or a few substances, mainly involving young people aged 15–24 years and among out-of-school adolescents[6, 9, 16]. Therefore, information about the burden of substance use among the school-going adolescents (10–19 years) is relevant to complement the existing literature and inform targeted interventions and potential policy decisions. This study assessed the prevalence of substance use and associated factors among secondary school adolescents in the Kilimanjaro region, northern Tanzania.

Methods

Study design, area, and population

We carried out a secondary analysis of data from a school-based cross-sectional study conducted in public secondary schools in four districts of the Kilimanjaro region, namely Moshi municipality, Moshi, Hai, and Siha districts, by the Institute of public health in Kilimanjaro Christian Medical University College (KCMUCO). The main aim was to assess the risk behaviors of adolescents attending public secondary schools. The study included all consenting form-one students who attended public secondary schools in 2019 from the selected four districts of the Kilimanjaro region. Kilimanjaro is one of the regions in the Northern part of Tanzania, comprising seven districts and covering 13250 Km2. Kilimanjaro has an estimated population of 1,640,087 people and an annual growth rate of 1.6%. The major economic activities in the region are agriculture and livestock keeping [20]. Kilimanjaro has many secondary schools compared to other regions, with 313 secondary schools (215 government, 98 private), making the region home to many adolescents who spend most of their time and days in school [21]. According to the country’s profile, adolescent accounts for 23% of Tanzania’s population, 13% and 10% for the 10–14 and 15–19 age groups, respectively [19].

Sampling, data collection methods, and tools

A multistage sampling technique was used to select 3227 adolescents. Four districts were purposefully selected in the first stage, ensuring rural-urban representativeness. The second stage was a random selection of public secondary schools from all available schools in each district. Only form-one students were included at the school level to build a cohort of repeated cross-sectional surveys in the following years. The purpose was to document trends of adolescent risk behaviors over four years period (i.e., form-one to four). Finally, a simple random sampling technique selected students proportional to the size of each school. Analysis was performed on 3224 adolescents after excluding three participants (0.1%) aged less than ten years and greater than 19 years of age.

The interviews were self-administered, using the Regional School Health Survey (RSHS) questionnaire adopted from the WHO/CDC Global Student Health Survey (GSHS) [22]. The RSHS questionnaire was standardized to assess risk behaviors among school-going students in Tanzania and administered in the Kiswahili language [8]. The tool has also been extensively used in other settings[15, 23, 24]. The risk behaviors in this survey included nutrition and participation in physical activity, personal hygiene, and substance use, including smoking, alcohol, illicit drugs, marijuana, khat use, experiences of violence and abuse, and risky sexual behaviors. Trained medical students from KCMUCo collected data. Before data collection, the data collectors explained the study purpose to all form one students and responded to all the questions asked before administering the interviews. The selected participants were then given the questionnaires and instructed to wait for further instructions from the data collectors. The next step was reading one question after another to ensure each respondent understood the question before filling out the questionnaire. The process continued until the last question. The data collectors made the necessary efforts to ensure privacy and confidentiality during the data collection. This was done by clearly explaining to participants why this was important and ensuring spaces between participants when completing the questionnaires.

Study variables

The dependent variable in this study was substance use. Lifetime substance use refers to using any substance at least once throughout the adolescent’s life [1, 2]. The substances considered in this study were alcohol, cigarette smoking, marijuana, khat, and recreational drugs (cocaine, heroin). Lifetime substance use was coded as “Yes” if an adolescent reported using any of the above substances and “No” if otherwise. Current substance use refers to using any of the following substances during the last 30 days preceding the interview: cigarette smoking, tobacco products, alcohol, recreational drug (cocaine and heroin), marijuana, khat, and amphetamines.

The independent variables included adolescent socio-demographic and behavioral characteristics. The demographic characteristics were adolescents age (10–14, 15–19 years), sex (male, female), schooling district (Moshi municipality council, Moshi district council, Siha, and Hai), and the number of days ever missed class (0 days, 1–3 days, ≥4 days). Social and behavioral variables were: parent/guardian use tobacco (neither, father or male guardian, mother or female guardian, both parents, don`t know), ever had sex (no, yes), number of sexual partners (1 partner, ≥2 partners), source of alcohol (shop/ street vendor, gave someone else to buy, friends, family, stole, some other way), frequency seen alcohol advertisement (never, rarely, sometimes, most times, always), frequency parents/guardian understood your problems (never, rarely, sometimes, most times, always), number of close friends (no friends, 1–5 friends, >6 friends), social support from friends (never, rarely, sometimes, most times, always), ever been bullied (no, yes), ever engaged in a physical fight (no, yes), and ever rode in a car with a drunk driver (no, yes).

Data processing and analysis

Data were cleaned and analyzed using SPSS software version 20. Descriptive statistics for substance use characteristics were summarized using frequencies and proportions for categorical variables. Continuous variables were summarized using mean and standard deviation. The Chi-square test determined the association between participant characteristics with lifetime and current substance use. Binary and multivariable logistic regression analysis estimated odds ratios (OR) and 95% confidence intervals (CI) for determinants of a lifetime and current substance use. A p-value of <0.05 was considered statistically significant in crude and adjusted analyses.

Ethical consideration

The Kilimanjaro Christian Medical University College Research and Ethics Review Committee (KCMU-CRERC) approved the parent study. All people aged 18 years and above provided oral informed consent. The headmasters from each secondary school assented to interview students aged <18 years because no invasive procedures required parental consent. Hence, the need for parental consent was waived by the ethics committee. Ethical approval for the current study was sought from the KCMU-CRERC and obtained approval ethical clearance certificate number PG04. The Institute Public Health director at KCMUCO provided permission to use the data. The study observed and protected the confidentiality and privacy of the subject’s data. Instead of adolescent names or any personal identifiers, unique identification numbers identified study participants.

Results

Participant socio-demographic characteristics

The mean age of 3224 adolescents (10–19 years) in this study was 14.6 years and a standard deviation of 1.07 years. More than half (53.5%) were aged 10–14, and just over half (53.0%) were females. Most adolescents included in this study schooled in Moshi (41.6%) and Siha (21.2%) district councils and Moshi municipality (20.7%). Few respondents, 103 (3.2%), reported missing class at least for four days or more (Table 1).

Table 1

Participant socio-demographic characteristics (N = 3224).

Variables	Frequency	Percentage
Age (years)
Mean (SD)	14.6 (1.07)
10–14	1726	53.5
15–19	1498	46.5
Sex
Male	1515	47.0
Female	1709	53.0
Schooling council
Moshi Municipality	667	20.7
Moshi district council	1342	41.6
Hai district council	533	16.5
Siha district council	682	21.2
Ever missed class
Did not miss class	2609	80.9
1–3 days	512	15.9
≥ 4 days	103	3.2

Self-reported prevalence of substance use

The lifetime and current prevalence of substance use was 19.7% and 12.8%, respectively. Among those who reported having ever used substances, the most common substance reported was alcohol (14.8%) and cigarette smoking (7.6%), followed by khat (1.6%), recreational drugs, specifically cocaine and heroin (0.7%), and marijuana (0.7%). The common substances reported among adolescents currently using substances were alcohol (8.2%) and cigarette smoking (4.3%) (Table 2).

Table 2

Self-reported prevalence of substance use (N = 3224).

Variable	Frequency	Percentage
Ever use substances †
Cigarette smoking	246	7.6
Alcohol	477	14.8
Recreational drugs *	23	0.7
Marijuana	23	0.7
Khat	51	1.6
Lifetime (overall) substance use
No	2590	80.3
Yes	634	19.7
Current use of any substance **†
Cigarette smoking	139	4.3
Tobacco smoking	40	1.2
Alcohol	264	8.2
Recreational drugs *	8	0.2
Marijuana	9	0.3
Khat	24	0.7
Amphetamines	51	1.6
Current use of any substance (overall)
No	2811	87.2
Yes	413	12.8

* Recreational drugs include both cocaine and heroin.

** Current substance use is within 30 days preceding the survey.

† Frequencies and percentages among those who answered “Yes”.

Adolescent social and behavioral characteristics

Among all the adolescents in this study, 13.5% had a father/male guardian in their family who was a smoker, compared to only 1.1% of mothers/female guardians. Among current alcohol users, most of them reported the source of alcohol was stealing (32%) and family members (30.8%). In addition, adolescents reported having always seen alcohol advertisements (15.3%), and few reported ever riding in a car with a drunk driver (4.5%) (Table 3).

Table 3

Participant’s social and behavioral characteristics (N = 3224).

Variables	Frequency	Percentage
Parents use tobacco *
Neither	2588	80.3
Father or male guardian	436	13.5
Mother or female guardian	36	1.1
Both parents	16	0.4
I do not know	144	4.5
Source of alcohol in the past 30 days (n = 264) *
From shop/street vendor	13	5.2
Gave someone else to buy	10	4.0
Friends	52	20.8
Family	77	30.8
Stole	80	32.0
Some other way	18	7.2
Seen alcohol advertisements *
Never	1690	52.4
Rarely	1034	32.0
Always	493	15.3
Ever had sex
No	2924	90.7
Yes	300	9.3
Number of sexual partners(n = 300) *
1 partner	118	41.5
≥ 2 partners	166	58.5
Number of close friends *
No friends	288	8.9
1–5 friends	2115	65.6
>6 friends	812	25.2
Received Social support from classmates *
Never	755	23.4
Rarely	1279	39.7
Always	1189	36.9
Parents/guardians understood your problems *
Never	822	25.5
Rarely	864	26.8
Always	1536	47.6
Ever been bullied
No	2785	86.4
Yes	439	13.6
Ever engaged in a physical fight
No	2486	77.1
Yes	738	22.9
Ever ridden in a car with a drunk driver
No	3079	95.5
Yes	145	4.5

*Frequencies and percentages do not add up due to missing values.

On the other hand, almost ten percent of adolescents reported having ever had sex (9.3%), of which 58.5% had two or more sexual partners. Nearly two-thirds (65.6%) reported having 1–5 close friends, and 47.6% said their parents always understood their problems. More than one-third (36.9%) reported always getting social support from their classmates. The self-reported prevalence of bullying was 13.6%. Furthermore, less than a quarter reported having ever engaged in a physical fight (22.9%) (Table 3).

Substance use by participant’s social-demographic and behavioral characteristics

There were no significant differences in the proportions of a lifetime and current substance use by adolescent age groups. The proportion of lifetime substance use differed significantly by participant characteristics (p<0.05). The proportion was higher among males (26.1%) compared to females (14.0%) and adolescents who missed class four days or more (29.1%) compared to those who did not (18.1%). In addition, the proportion of lifetime substance use was significantly higher among adolescents who: ever had sex (55.7), ever bullied (32.1%), ever engaged in a physical fight (32.8%), always seen alcohol advertisements (29.9%), and adolescents whose parents rarely understood their problems (25.0%) compared to their counterparts (Table 4).

Table 4

Substance use by participant characteristics (N = 3224).

Variable	Total (%)	Lifetime use	P-value	Current use *	P-value
		n (%)		n (%)
Age
10–14	1726 (53.5)	319 (18.5)	0.07	213 (12.3)	0.392
15–19	1498 (46.5)	315 (21.0)		200 (13.4)
Sex
Male	1515 (47.0)	395 (26.1)	<0.001	261 (17.2)	<0.001
Female	1709 (53.0)	239 (14.0)		152 (8.9)
District
Moshi MC	667 (20.7)	142 (21.3)	<0.001	93 (13.9)	0.001
Moshi DC	1342 (41.6)	310 (23.1)		201 (15.0)
Hai	533 (16.5)	89 (16.9)		50 (9.4)
Siha	682 (21.2)	93 (13.6)		69 (10.1)
Days missed class
Did not miss class	2609 (80.9)	473 (18.1)	<0.001	307 (11.8)	0.001
1–3 days	512 (15.9)	131 (25.6)		86 (16.8)
≥ 4 days	103 (3.2)	30 (29.1)		20 (19.4)
Ever had sex
No	2924 (90.7)	467 (16.0)	<0.001	292 (10.0)	<0.001
Yes	300 (9.3)	167 (55.7)		121 (40.3)
Ever been bullied
No	2785 (86.4)	493 (17.7)	<0.001	311(11.2)	<0.001
Yes	439 (13.6)	141(32.1)		102(23.2)
Seen alcohol advertisement **
Never	1690 (52.4)	246 (14.6)	<0.001	152 (9.0)	<0.001
Rarely	1034 (32.0)	241 (23.3)		165 (16.0)
Always	493 (15.3)	147 (29.9)		94 (19.1)
Ever engaged in a physical fight
No	2486 (77.1)	392 (15.8)	<0.001	239 (9.6)	<0.001
Yes	738 (22.9)	242 (32.8)		174 (23.6)
Parents/guardians understood your problems *
Never	822 (25.5)	246 (21.0%)	<0.001	152 (12.5)	<0.001
Rarely	864 (26.8)	241 (25.0%)		165 (17.6)
Always	1536 (47.6)	147 (16.0%)		94 (10.8)
Classmate social support **
Never	755 (23.4)	174 (23.1)	<0.001	113 (15.0)	0.001
Rarely	1279 (39.7)	272 (21.3)		182 (14.2)
Always	1189 (36.9)	188 (15.8)		118 (9.9)

* Current use is within 30 days before the survey.

** Frequencies and percentages do not add up due to missing values.

Likewise, the proportion of current substance use was significantly higher among male adolescents (17.2%), those who missed class four days and more (19.4%), and those who ever had sex (40.3%) which was about four times higher than those who never had sex. Furthermore, the proportion of current substance use was significantly higher among those who had always seen alcohol advertisements (19.1%), ever engaged in a physical fight (23.6%), and whose classmate(s) never showed social support (15.0%) compared to their counterparts (Table 4).

Adjusted analysis for factors associated with substance use

Significantly lower odds of lifetime substance use were among female adolescents compared to males (AOR = 0.61, 95%CI 0.50–0.74), those from Siha district (AOR = 0.64 95%CI 0.47–0.87) compared to Moshi municipal council, and whose classmates always showed social support (AOR = 0.73, 95%CI 0.57–0.95). Higher odds of lifetime substance use were among adolescents who have ever had sex (AOR = 4.50, 95%CI 3.60–6.13), ever been bullied (AOR = 1.50, 95%CI 1.17–1.94), ever engaged in a physical fight (AOR = 2.03, 95%CI 1.65–2.50), and always seen alcohol advertisements (AOR = 2.09, 95%CI 1.61–2.70) (Table 5).

Table 5

Adjusted analysis for factors associated with substance use (N = 3224).

Variable	Lifetime substance use		Current substance use
	AOR† (95%CI)	P-value	AOR† (95% CI)	P-value
Age
10–14	1.00		1.00
15–19	1.09 (0.70,1.32)	0.378	0.97 (0.77,1.22)	0.78
Sex
Male	1.00		1.00
Female	0.61 (0.50,0.74)	<0.001	0.63 (0.50,0.80)	<0.001
District
Moshi MC	1.00		1.00
Moshi DC	1.22 (0.96,1.57)	0.107	1.14 (0.86,1.52)	0.374
Hai	0.91 (0.66, 1.25)	0.57	0.77 (0.52,1.14)	0.193
Siha	0.64 (0.47, 0.87)	0.005	0.78 (0.55, 1.12)	0.180
Ever had sex
No	1.00		1.00
Yes	4.50 (3.60,6.13)	<0.001	4.31 (3.25,5.71)	<0.001
Days missed class
Did not miss class	1.00		1.00
1–3 days	1.40 (1.09, 1.78)	0.007	1.33 (1.00,1.76)	0.049
≥ 4 days	1.31 (0.80,2.14)	0.287	1.09 (0.62, 1.94)	0.75
Ever been bullied
No	1.00		1.00
Yes	1.50 (1.17,1.94)	0.002	1.55 (1.16, 2.05)	0.003
Seen alcohol advertisement
Never	1.00		1.00
Rarely	1.44 (1.16,1.79)	0.001	1.50 (1.16, 1.93)	0.002
Always	2.09 (1.61,2.7)	<0.001	1.87 (1.37, 2.53)	<0.001
Ever engaged in a physical fight
No	1.00		1.00
Yes	2.03 (1.65, 2.5)	<0.001	2.19 (1.73, 2.78)	<0.001
Parents/guardians understood your problems
Never	1.00		1.00
Rarely	1.16 (0.90, 1.49)	0.253	1.38 (1.03,1.85)	0.034
Always	0.81 (0.64,1.03)	0.860	0.90 (0.68, 1.21)	0.487
Classmate social support
Never	1.00		1.00
Rarely	0.89 (0.70, 1.13)	0.327	0.89 (0.68,1.18)	0.423
Always	0.73 (0.57, 0.95)	0.017	0.71 (0.53, 0.97)	0.029

† AOR: Adjusted Odds Ratio.

Furthermore, lower odds of current substance use were among female adolescents (AOR = 0.63, 95%CI 0.50–0.80) and whose classmates always showed social support (AOR = 0.71, 95%CI 0.53–0.97). The adolescents who ever had sex (AOR = 4.31, 95% CI 3.25–5.71), were bullied (AOR = 1.55, 95% CI 1.16–2.05), engaged in a physical fight (AOR = 2.19, 95% CI 1.73–2.78), always seen alcohol advertisements (AOR = 1.87, 95% CI 1.37–2.53), and whose parent/guardians rarely understood their problems (AOR = 1.38, 95% CI 1.03–1.85) had higher odds of current substance use (Table 5).

Discussion

The study aimed to determine the prevalence and factors associated with substance use among secondary-school adolescents in the Kilimanjaro region, Northern Tanzania. The lifetime and current prevalence of substance use was 19.7% and 12.8%, respectively. The most prevalent substances used were alcohol and cigarette smoking. Factors significantly associated with lifetime and current substance use included: sex (high among males), ever having sex, being bullied, ever in a physical fight, seeing alcohol advertisements, classmate’s social support, and parents/guardians understanding adolescents’ problems.

The lifetime prevalence (19.7%) of substance use among adolescents in this study is higher than 7% from the 2006 Tanzanian Global School-based Student Health Surveys (GSHS) [9]. Current substance use in this study is also higher than the 2017 GSHS, which reported specifically alcohol (4.5%), drugs (3.1%), tobacco (5.1%), and cigarette smoking (4.5%) [8]. A study in Dodoma reported a higher prevalence of substance use, specifically alcohol (19.8%), smoking cigarettes (7.4%), and marijuana (3.3%) among adolescents aged 15–17 years [25]. The current prevalence (12.8%) of substance use in this study is lower than the WHO Global Alcohol status report on current use (21.4%) among adolescents aged 15–19 years in African regions [7] and a study done among adolescents in Ethiopia (47.9%) [26]. The possible explanation for the difference may be reporting only one substance in other studies, sample size variations, and adolescent age. Compared to the national 2006 and 2015 GSHS studies, the findings show a higher prevalence, possibly because of the small geographical coverage in this study. These findings demonstrate a need to strengthen regulatory measures to reduce substance use, particularly alcohol and cigarette smoking.

We found no significant association between adolescent age and substance use. However, previous studies in Zambia [27] and Benin [28] in west Africa found high substance use practice among adolescents 15+ years. Likewise, analysis of GSHS data from six Asian low- and middle-income countries revealed a higher risk of substance use (alcohol and smoking) among older compared to younger adolescents [29]. However, there are limited studies about the association between adolescent age and substance use in SSA. Despite the observed differences with other studies, interventions should target reducing substance use practice among school-going adolescents because of their ingenuity in trying new things.

In this study, female adolescents had lower odds of using substances than males, similar to other studies in Morocco, Zimbabwe, and Ethiopia [26, 30, 31]. Alcohol use (among other substances) is also common among sexually active adolescent males in SSA [32]. Lower odds of substance use among females may be associated with societal and cultural gender role expectations to act and conduct themselves. Substance use among females is seen as a shameful, inappropriate practice and less sensation-seeking behavior than males [26, 30, 31].

Adolescents who reported ever having sex were significantly more likely to be lifetime and current substance users. Likewise, in Tanzania, young people aged 15–24 years using alcohol were more likely to engage in risky sexual behaviors [6]. A study in SSA associated sexual behaviors with alcohol use [32]. The finding is also consistent with studies in Iran and Bangladesh that associated the experience of sexual activity with substance use [24, 33]. The observed association may be because substances such as alcohol, cigarette, and illicit drugs affect cognitive processes and decision-making, thus contributing to a compromised judgment [24, 33]. Also, sexual activity during these periods can make adolescents vulnerable to developing mental disorders like depression or anxiety, which, in turn, could lead them to use substances [24]. Health education interventions on the effects and consequences of substance use should be enhanced in secondary schools [8].

As reported elsewhere, adolescents who have ever been bullied had higher odds of a lifetime and current substance use [34]. A possible reason for this is that the victims of bullying are predisposed to use substances as a maladaptive coping strategy [34]. In addition, a study in Thailand found that engaging in a physical fight was associated with alcohol use and misuse, where adolescents used substances as a coping mechanism [35]. Likewise, we also found that adolescents who engaged in a physical fight had a higher likelihood of substance use, similar to a study done across eight sub-Saharan countries [36]. Therefore, adolescents need to be educated on the psychological effects that bullying and physical fights can cause, explaining how victimization can cause severe depression and anxiety that lead to substance use [37]. Student support groups or systems for the affected may help the victims cope with the bullying and physical abuse, reducing dependence on substance use.

Adolescents who reported always seeing alcohol advertisements were more likely to use substances. Likewise, advertising alcoholic beverages in the mass media promoted abusive alcohol consumption in Italy [38]. Adolescents exposed to alcohol advertising are more likely to start consuming alcohol earlier and drink large amounts [39]. A systematic review also demonstrated the relationship between alcohol advertisements and increased consumption among adolescents [40]. These findings indicate the need to limit alcohol advertisements in the media or ensure they portray their adverse effects. They also suggest prohibiting selling, buying, and posting substances on school premises, especially among school-going and out-of-school adolescents [41].

This study’s findings also show that adolescents whose classmates always showed social support were less likely to use substances. These findings are consistent with the study done in Bangladesh, which reported that the likelihood of substance use increases with a lack of peer support as it exhibits greater anti-social behaviors that can manifest in substance use [24]. In Malaysia, adolescents with inadequate peer support had a higher likelihood of substance use [42]. On the contrary, a study done in Ghana found no association between peer support and substance use [34]. The possible reasons could be that the study only assessed two substances, i.e., cannabis and amphetamines, compared to over five substances this study examined.

In addition, adolescents whose parents rarely understood their problems were more likely to use substances. Previous studies demonstrated that parents’ supervision of adolescents reduces substance use practice [27, 43]. Limited parental monitoring, involvement, and active substance use in the home at the family level may predispose adolescents to use substances [44]. Therefore, lack of social support may expose adolescents to substance use practices as a coping mechanism due to insecurity.

Study strengths and limitations

This study used a large sample size of 3224 adolescents from public secondary school schools in four districts of the Kilimanjaro region. Large sample size and wider geographical coverage enhance precision and study’s representativeness, respectively. This study is one of the first in our setting to measure substance use’s prevalence and associated factors. The study also estimated the burden of a lifetime and current substance use, specifically among adolescents aged 10–19 years, and associated factors, which is essential to inform necessary interventions.

The study had several limitations. Firstly, the study design is cross-sectional; hence cannot determine the temporal relationship between substance use and the associated factors. Secondly, the study collected data among adolescents attending public secondary schools. Thus, the results may not reflect students in private schools and out-of-school adolescents. Thirdly, the questionnaire used for data collection was adopted from the WHO/CDC Global Student Health Survey [22]. This tool does not capture all the factors associated with substance use. These factors include the place of upbringing, social sanctions, belief systems, self-control, cultural acceptance of substance use, and availability and accessibility of substances, particularly drugs and cigarettes/tobacco products[24, 26, 45]. The tool does not also capture the consequences of substance use among school-going adolescents. Lastly, there was also a possibility of recall and social-desirability bias where adolescents might have forgotten or answered what they thought was socially desirable. Such bias may either over or under-estimate the prevalence of substance use.

Conclusion and recommendations

The study reflects the high prevalence of substance use among adolescents in the Kilimanjaro region. Alcohol and cigarette are the most prevalent substances used. The factors significantly associated with substance use were sex (high among males), ever having sex, being bullied, ever in a physical fight, seeing alcohol advertisements, classmate’s social support, and parents/guardians understanding adolescents’ problems. The study recommends that students’ leadership, with support from the teachers, create support groups or clubs that may help adolescents share alternative healthy ways of coping/dealing with stress, anxiety, and depression caused by bullying, which leads them to rely on substance use. The government should adopt regulatory measures to limit the number of alcohol advertisements the media portrays. Monitoring adolescents’ prohibition of selling and buying any substance such as alcohol and tobacco products is crucial in or near the school premises.

27 Apr 2022

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Reviewer #2: Yes

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Reviewer #1: The authors of the manuscript; Prevalence of substance use and associated factors among secondary school adolescents in the Kilimanjaro region, northern Tanzania” sought to determine the prevalence of substance use and associated factors among secondary school adolescents in the Kilimanjaro region, Northern Tanzania. The authors report that the prevalence of substance use among school-going adolescents was higher than in previous studies conducted in Tanzania, with alcohol and cigarette us, being the most common substances used. They also noted sociodemographic and behavioral factors associated with substance use in this population. Overall, this manuscript is well written. However, there are some comments below for the authors to consider that would help improve the manuscript’s overall readability.

General comments: Please read entire manuscript thoroughly for typos and missing articles, incomplete sentences. I mentioned some below; but please cross-check the entire manuscript.

Abstract:

1. There is a typo in first sentence in the methods; missing “of”

2. Typo in second sentence in the methods; missing “were summarized”

3. “We used logistic regression to obtain odds ratios and 95% confidence intervals (CI) for risk factors associated with differences in PA”. What is PA?

4. “Multivariable logistic regression models was used to obtain odds ratios and 95% confidence intervals (CI)”. CI has been previously defined…

Background:

1. Typo in this sentence (missing aged): “Substance use has increased in recent years and is a growing public health problem and a worldwide threat, significantly affecting young people 10-24 years”

2. “For example, in developed countries, the estimated risk of developing drug dependence on cannabis uses alone…”; change uses to use

3. After looking it up, bhang seems to be marijuana? Can the authors clarify, many people in the international audience may not be familiar with the word..

Methods:

1. Please define KCMUCO

2. Please rewrite the following sentence; unclear as currently written: “A total of 3224 for the current study was analyzed data for adolescents after excluding three (0.1%) individuals aged less than ten and greater than 19 years.”

3. “Trained students of Doctor of Medicine to collect data.” Sentence is not complete.

4. “Lifetime substances use was defined as using any substance at least once in their lifetime”. Remove “s” from behind “substances”

5. Were the same substances examined for lifetime use, also examined for current use? I ask because I see amphetamines examined in current use, but not mentioned in lifetime use under the subsection “outcome and explanatory variables”. Can the authors clarify?

6. Did the authors consider source of the other substances examined besides alcohol as covariates? How did the authors select the independent variables to include in their study?

7. The authors can use one: crude or unadjusted

Results: I suggest that the authors redo or recheck the analysis they have presented in the results section; as well as the table arrangement and ordering.

1. I am not sure why the authors presented Table 3 before table 2 in their manuscript. Tables are supposed to be ordered…Table 1, Table 2….The authors should rearrange the way the results were presented or change the Table numbering so it’s sequential.

2. Can the %s come after the corresponding sentences/statements as the previous sentences? “…few adolescents (15.3%) reported having always seen alcohol advertisements and (4.5%) had ever rode in a car with a drunk driver.”

3. There are two table 2’s in this manuscript. Authors should correct this error. Also, are the percentages presented in the table for Substance use by participant characteristics, for the lifetime and current use row percentages or column percentages? Where are these numbers from? They are not adding up to 100. Can the authors clarify what they have done? Also, it would help if the authors put the n’s for the lifetime and current use in the table.

4. There are two table 3’s? Manuscript jumps from Table 4, in the results to Table 6, no mention of Table 5. Authors should arrange their results accordingly.

5. Last table: the authors mentioned in the methods that they presented crude/unadjusted and adjusted Cis…I do not see it presented in the tables. Can the authors clarify…

Discussion:

1. “The lifetime prevalence of substance use among adolescents in this study is high than the 2006 and 2017 Tanzanian Global School-based Student Health Surveys (GSHS)”. There is a typo in this sentence, change “high” to “higher”

2. When the authors are comparing prevalence to other studies in the discussion, they should remind the readers what prevalence they are comparing by providing the numbers they obtained in their study for comparison.

3. Can the authors provide more insight as to why they did not find a significant association between adolescent age and substance use in their current study?

3. Why is this sentence written this way with a period after the first sentence?: "These findings are consistent with the study done in Bangladesh. Which reported that the likelihood of substance use increases with a lack of peer support as it exhibits greater anti-social behaviors that can manifest to substance use"

Reviewer #2: TITLE

Prevalence of substance use and associated factors among secondary school adolescents in Kilimanjaro region, Northern Tanzania.

OVERALL COMMENTS

The study is an important contribution to the knowledge of the prevalence of substance use in Tanzania, specifically the Kilimanjaro region. Findings, especially factors related to substance use could influence policymakers in where to channel resources in dealing with the burden of substance abuse in the region. However, I recommend that the authors address these concerns below:

1. The study should mention some policies or efforts made to curb substance use amongst adolescents in Tanzania. It is worth mentioning if there is no policy at all. This could highlight the shortfalls in policies.

2. The study needs a conclusion to emphasize the results and clearly outline recommendations. It can also make suggestions for future studies.

3. The authors should consider using the assistance of a professional editor to correct grammatical and typing errors.

SPECIFIC COMMENTS

Abstract

1. The abstract has major grammatical errors that need to be addressed. I suggest authors use the assistance of a professional editor.

2. The statement in line 7, ‘...and whose parent/guardians rarely understood their problems’, is unclear and needs revision.

3. The sentence “The study used secondary data from a cross-sectional study adolescents aged 10- 19 years from public secondary schools in the Kilimanjaro Region, northern Tanzania” should be revised as “The study used secondary data from a cross-sectional survey of adolescents aged 10- 19 years from public secondary schools in the Kilimanjaro Region, northern Tanzania”

4. “Substance use was measured using the Global School Health Survey (GSHS) questionnaire.” – You should be as specific as possible.

5. What does “PA” stand for?

6. Similar factors [were] associated with lifetime substance users.

7. You indicated in the conclusion that “The prevalence of substance use among school-going adolescents in this study is higher than the previous studies in Tanzania …”. This conclusion is not directly derived from the study and should be deleted. Please note that your conclusion should exclusively be based on your results.

Background

In the last paragraph, the authors mention other studies focusing on only a few substances used by adolescents. Studies by Mnyika et al. in 2011, evaluated various substances used by adolescents in the region. I suggest authors rather focus on factors influencing substance use, as this was missing in other studies.

Methods

1. The last statement of the study design and population, ‘…According to the countries profile, adolescent accounts for 23% of Tanzania’s population, 13% and 10% for 10-14, 15-19 age groups,’ is unclear and need to be rephrased.

2. In the sampling data collection methods and tools, authors should consider rephrasing the first sentence of the second paragraph. Consider ‘Data was collected by medical students’, since the study has already been done.

3. Line 8 of the second paragraph of the sampling data, collection methods and tools should be revised. ‘the point ‘Trained medical students collected the data’ had been mentioned in line 1.

4. Authors should mention sources of stealing of substances as a limitation of the study and give future recommendations for other studies.

5. Table 2, statistics on number of sexual partners needs realignment.

Discussion

1. Authors need to provide the 2006 and 2015 GSHS statistics that were compared to the study.

2. The study, done in Ghana that found no association between peer support and substance use, needs to be cited.

3. Authors were able to compare each of the significant factors that were associated with adolescent substance use in the area to existing literature. However, they failed to compare the prevalence of other recreational substances like khat and methamphetamines to that of existing literature. They only compared alcohol, cigarettes, and marijuana, but no discussion on the other recreational substances.

Strengths and Limitations

The study in 2011 by Mnyika et al., titled ‘Prevalence of and predictors of substance use among adolescents in rural villages of Moshi district, Tanzania’, assessed substance use amongst adolescents. Moshi District was included in this study. I suggest you revise this statement that says this study is the first to be done in the region. Consider saying it is the first that includes associated factors to substance use.

Conclusion

The authors concluded that ‘The study’s prevalence of substance use is higher than the previous 2006 and 2015 Tanzania Global School-based Student Health Surveys’. This inference does not relate to the study results. The findings of the study did not result in this conclusion. I suggest the authors make concluding statements based on the findings of this study.

References

Reference No. 1 has the name of main author missing from lists of authors.

Minor Comments

1. In the Methods (p.6), you used “outcome”, “explanatory”, and “dependent” variable interchangeably. However, these terms are qualitatively different. In your case, it involves “substance use”, so I will suggest that you should use “dependent” variable throughout the paper.

**********

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Reviewer #1: No

Reviewer #2: No

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30 May 2022

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Response: We have revised the entire manuscript to make sure it meets the journal requirements.

2. Please provide additional details regarding participant consent. In the Methods section, please ensure that you have specified (1) whether consent was informed and (2) what type you obtained (for instance, written or verbal). If your study included minors, state whether you obtained consent from parents or guardians. If the need for consent was waived by the ethics committee, please include this information.

Response: Information about the type of consent and assent added in the ethics consideration section.

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Response: The manuscript was prepared in a word document and not in LaTex. Please advise if the entire manuscript is required to be transferred to LaTex and be re-submitted.

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Response: Apologies for this confusion. The data have not been deposited in a repository. The authors do not have a legal permission to share the data used in this study. All data requests should be directed to the Institute of Public Health Director at KCMUCo through iph@kcmuco.ac.tz.

5. Please amend the manuscript submission data (via Edit Submission) to include author Ahmed Y. Nyaki, Beatrice J. Leyaro, Redempta Mamseri, Johnston

George, James S. Ngocho and Innocent B. Mboya.

Response: The manuscript submission has been amended to include all authors.

Reviewer reports:

Reviewer #1:

Overall, this manuscript is well written, however there are some comments below for the authors to consider that would help improve the manuscript’s overall readability.

Response: We thank the reviewer for the very positive comment. We have revised the manuscript as recommended by the reviewer following the details below.

General comments: Please read entire manuscript thoroughly for typos and missing articles, incomplete sentences.

Response: The manuscript has been thoroughly revised to correct for grammatical errors.

Abstract

1. There is a typo in first sentence in the methods; missing “of”,

Response: Thank the reviewer for this comment, the typo has been corrected

2. Typo in second sentence in the methods: missing “were summarized”

Response: Thank the reviewer for this comment, the typo has been corrected

3. We used logistic regression to obtain odds ratio and 95% Confidence interval (CI) for risk factors associated with differences in PA what is PA,

Response: We are sorry for this confusion. This was a typo and it is corrected to read “We used logistic regression to obtain odds ratios and 95% confidence intervals (CI) for risk factors associated with substance use”.

4. “Multivariable logistic regression models was used to obtain odds ratios and 95% confidence interval CI”.CI has been previously defined.

Response: We acknowledge the comment, it has been addressed, and deleted the repeated sentence.

Background

1 Typo in this sentence (missing aged). “Substance use has increased in recent years and is a growing public health problem and a worldwide threat, significantly affecting young people 10-24 years”

Response: We acknowledge the typo and have addressed it.

2 “For example, in developing countries risk of developing drug dependence on cannabis, uses alone changes uses to use

Response: Thank you for pointing out the typo, we have addressed it.

3. After looking it up, bhang seems to be marijuana? Can the authors clarify, many people in the international audience may not be familiar with the word.

Response: We acknowledge the comment, and we have addressed it by adding in brackets the word “marijuana”, it was written bhang because, the global school initiative out of school children study was done in Tanzania, which aimed to determine the factors to why most children are out of school or dropouts. Smoking marijuana was one of the factors and the local language used by many students was “Bhang”.

Methods

1. Please Define KCMUCo.

Response: KCMUCo has been stated clearly in the methodology.

2. Please re write the following sentence: unclear as currently written. “A total of 3224 for the current study was analyzed fata for adolescents after excluding three (0.1%) individuals aged less than ten and greater than 19 years”.

Response: We acknowledge the typo and clarified the sentence to read, “A total sample of 3224 adolescents was analyzed for the current study, after excluding three participants (0.1%) that were aged less than 10 years and greater than 19 years of age”.

3. “Trained Students of Doctor Of medicine to collect data is not complete”.

Response: Thank you so much for the comment, we corrected it to read “Trained medical students from KCMUCo collected data”.

4. “Lifetime substance use was defined as using any substance at least once in their lifetime” remove “s” from behind “substances”.

Response: Thank you for pointing out the typo, we have addressed it.

5. Were the same substance examined for lifetime use, and also examined for current use? I as because I see amphetamines examined in current use, but not mentioned in lifetime use under the subsection “outcome and explanatory variables”. Can the author clarify?

Response: We thank the reviewer for this comment. The data collection tool was adopted from the WHO/CDC Global Student Health Survey (GSHS). In the assessment tool, the substances assessed for lifetime use were alcohol, cigarette smoking, marijuana, khat, recreational drugs (cocaine, heroin) while for current use, it was cigarette smoking, tobacco products, alcohol, recreational drug (cocaine and heroin), marijuana, khat, and amphetamines.

6. Did the authors consider the source of the other substances examined besides alcohol as covariates? How did the authors select the independent variables to include in their study?

Response: As indicated above, the assessment tool used was adopted from the WHO/CDC Global Student Health Survey (GSHS). So, as one of the limitations, it only assessed sources of alcohol and no other substances. The variables in this study were chosen in reference to the conceptual framework (Ludick and P’Olak, 2016) and past studies that used almost the same assessment tool adopted from WHO.

7. The author can use one crude/unadjusted

Response: We thank the reviewer for this comment, we acknowledge and chose to use one of these two words.

Results

General comment:

Results: I suggest that the authors redo or recheck the analysis they have presented in the results section; as well as the table arrangement and ordering

Response: We acknowledge the reviewer’s comment, and we have rearranged the tables and correctly numbered them to match the explanation in the results section.

1. I am not sure why the authors presented Table 3 before table 2 in their manuscript. Tables are supposed to be ordered…Table 1, Table 2….The authors should rearrange the way the results were presented or change the Table numbering so it’s sequential.

Response: We acknowledge the reviewer’s comment, and we have rearranged the tables and correctly numbered them to match the explanation in the results section

2. Can the %s come after the corresponding sentences/statements as the previous sentences? “…few adolescents (15.3%) reported having always seen alcohol advertisements and (4.5%) had ever rode in a car with a drunk driver.”

Response: We thank the reviewer for this comment, we corrected the statements to read “In addition, adolescents reported having always seen alcohol advertisements (15.3%), and few reported to ever rode in a car with a drunk driver (4.5%)”.

3. There are two table 2’s in this manuscript. Authors should correct this error. Also, are the percentages presented in the table for Substance use by participant characteristics, for the lifetime and current use row percentages or column percentages? Where are these numbers from? They are not adding up to 100. Can the authors clarify what they have done? Also, it would help if the authors put the n’s for the lifetime and current use in the table.

Response: We acknowledge the reviewer’s comment, and we have correctly numbered the tables to match the explanation in the results section. The lifetime and current use row or column percentages don’t add up to 100% because, as we noted below table 2, that the “frequencies and percentages presented are among those who answered “Yes” to ever used or currently using any substance. The numbers for the lifetime and current use all add up to “N= 3224” which is on the first line on table 2.

4. There are two table 3’s? Manuscript jumps from Table 4, in the results to Table 6, no mention of Table 5. Authors should arrange their results accordingly.

Response: We acknowledge the reviewer’s comment, and we have rearranged the tables and correctly numbered them to match the explanation in the results section

5. Last table: the authors mentioned in the methods that they presented crude/unadjusted and adjusted is…I do not see it presented in the tables. Can the authors clarify?

Response: We thank the reviewer for this comment. We have corrected the typo, as it was aimed to only present the adjusted analyses results. This was to reduce having many tables in this manuscript, hence it sufficed to only report the adjusted analysis results.

Discussion.

1. “The lifetime prevalence of substance use among adolescents in this study is high than the 2006 and 2017 Tanzanian Global School-based Student Health Surveys (GSHS)”. There is a typo in this sentence, change “high” to “higher”

Response: Thank the reviewer for this comment, the typo has been corrected

2. When the authors are comparing prevalence to other studies in the discussion, they should remind the readers what prevalence they are comparing by providing the numbers they obtained in their study for comparison.

Response: We thank the reviewer for this comment, we acknowledge the inputs and changed the statements to include the prevalence of the other studies to remind the reader of what exactly we comparing.

3. Can the authors provide more insight as to why they did not find a significant association between adolescent age and substance use in their current study?

Response: We would like to clarify this that we did find an association between adolescents age and substance use in our current study, but the association was not statistically significant (P value was greater than 0.05), due to a little difference in the frequencies of the ages 10-14 (n= 1726 (53.5%) and 15-19 (n=1498 (46.5%)).

4. Why is this sentence written this way with a period after the first sentence? "These findings are consistent with the study done in Bangladesh. Which reported that the likelihood of substance use increases with a lack of peer support as it exhibits greater anti-social behaviors that can manifest to substance use"

Response: We acknowledge the reviewer’s comment and corrected that statement to read” These findings are consistent with the study done in Bangladesh, which reported that the likelihood of substance use increases with a lack of peer support as it exhibits greater anti-social behaviors that can manifest to substance use”.

Reviewer #2:

Overall comments, the study is an important contribution to the knowledge of the prevalence of substance use in Tanzania, specifically the Kilimanjaro region. Findings, especially factors related to substance use could influence policymakers in where to channel resources in dealing with the burden of substance abuse in the region. However, I recommend that the authors address these concerns below:

Response: We sincerely appreciate the reviewer for the very positive comment. We hope the manuscript can be accepted for publication after addressing the reviewer and editorial comments.

1. The study should mention some policies or efforts made to curb substance use amongst adolescents in Tanzania. It is worth mentioning if there is no policy at all. This could highlight the shortfalls in policies.

Response: we acknowledge the reviewer’s comment, though we did mention in the background section, that the intervention and development strategies presenting the country mainly address adolescent issues most focus on HIV and sexual and reproductive health (SRH). We will include the lack of policy as well that address substance issues among adolescents.

2. The study needs a conclusion to emphasize the results and clearly outline recommendations. It can also make suggestions for future studies.

Response: we thank you the reviewer for this comment, we did change the conclusion and included few recommendations.

3. The authors should consider using the assistance of a professional editor to correct grammatical and typing errors.

Response: We thank the reviewer for this comment. The manuscript has been thoroughly revised for grammar.

Abstract

1. The abstract has major grammatical errors that need to be addressed. I suggest authors use the assistance of a professional editor.

Response: We acknowledge the reviewer comment. The manuscript has been thoroughly revised for grammar.

2. The statement in line 7, ‘...and whose parent/guardians rarely understood their problems’, is unclear and needs revision.

Response: Thank you for this comment, we have addressed it. The statement now reads “adolescents whose parent/guardians rarely understood their problems”

3. The sentence “The study used secondary data from a cross-sectional study adolescents aged 10- 19 years from public secondary schools in the Kilimanjaro Region, northern Tanzania” should be revised as “The study used secondary data from a cross-sectional survey of adolescents aged 10- 19 years from public secondary schools in the Kilimanjaro Region, northern Tanzania”

Response: we acknowledge the comment and have addressed it.

4. “Substance use was measured using the Global School Health Survey (GSHS) questionnaire.” – You should be as specific as possible.

Response: Details about the measurement of substance use in the GSHS are provided in the first paragraph of the study variables section.

5. What does “PA” stand for?

Response: We acknowledge the comment/ This was a typo as well, and it is corrected to read “We used logistic regression to obtain odds ratios and 95% confidence intervals (CI) for risk factors associated with substance use”.

6. Similar factors [were] associated with lifetime substance users.

Response: Thank you for pointing out the typo, we have addressed it.

7. You indicated in the conclusion that “The prevalence of substance use among school-going adolescents in this study is higher than the previous studies in Tanzania …” This conclusion is not directly derived from the study and should be deleted. Please note that your conclusion should exclusively be based on your results.

Response: we thank you the reviewer for this comment, we did change the conclusion to be based on our study results, which reads “The study reflects high prevalence of substance use among adolescents in Kilimanjaro region. Alcohol and cigarette are the most prevalent substances used. Regulatory measures are essential to limit alcohol advertisements that are media portrayed. Efforts are needed to reduce risk behaviors that such as physical violence and bullying, through peer support groups/clubs in school environments.”

Background

In the last paragraph, the authors mention other studies focusing on only a few substances used by adolescents. Studies by Mnyika et al. in 2011, evaluated various substances used by adolescents in the region. I suggest authors rather focus on factors influencing substance use, as this was missing in other studies.

Response: We thank the reviewer for this comment and pointing out the work by Mnyika et al (2011). However, our mentioning of “studies in other settings” was not specific to only those studies conducted Kilimanjaro region. Nevertheless, although Mnyika et al (2011) focused on alcohol and cigarette smoking, the study population was primary school students (standard 6 and 7) compared to form one (secondary school) students in this study. Our analysis included alcohol and tobacco use, among other substances. However, we acknowledge the point raised by the reviewer on identifying the factors associated with substance use, which was what we wanted to establish in this study.

Methods

1. The last statement of the study design and population, ‘…According to the country’s profile, adolescent accounts for 23% of Tanzania’s population, 13% and 10% for 10-14, 15-19 age groups,’ is unclear and need to be rephrased.

Response: Thank you for pointing out the typo, we have addressed it. The statements read, “According to the country’s profile, adolescent accounts for 23% of Tanzania’s population, 13% and 10% for the 10-14 and 15-19 age groups respectively”

2. In the sampling data collection methods and tools, authors should consider rephrasing the first sentence of the second paragraph. Consider ‘Data was collected by medical students’, since the study has already been done.

Response: Thank you so much for the comment, we corrected it to read “Trained medical students from KCMUCo collected the data.”

3. Line 8 of the second paragraph of the sampling data, collection methods and tools should be revised, ‘the point ‘Trained medical students collected the data’ had been mentioned in line 1.

Response: Thank you for pointing out the typo, we have addressed it and deleted the repeated statement.

4. Authors should mention sources of stealing of substances as a limitation of the study and give future recommendations for other studies.

Response: Indeed, the tool did not capture a lot of other key factors that could explain substance use among adolescents in this study. We have highlighted such factors in the second paragraph of the study strengths and limitations and provided relevant citations.

5. Table 2, statistics on number of sexual partners needs realignment

Response: we appreciated this comment which we would like to clarify. The number of sexual partners variables, the frequencies indicated was among those who responded yes to “ever had sex” that was (n=300) as indicated on the side of the variable, the * indicates there were missing frequencies of those who didn’t responded to how many sexual partners they had.

Discussion

1. Authors need to provide the 2006 and 2015 GSHS statistics that were compared to the study.

Response: We thank you the reviewer for this comment, we have addressed it and the statistics are provided in the statements which reads “The lifetime prevalence (19.7%) of substance use among adolescents in this study is higher than the 2006 Tanzanian Global School-based Student Health Surveys (GSHS) which was 7%. For current substance use in this study is also higher than the 2017 GSHS which reported specifically alcohol (4.5%), drugs (3.1%), tobacco (5.1%) and cigarette smoking (4.5%) but had no overall estimate. This information has been added at the beginning of the second paragraph of the discussion section.

2. The study, done in Ghana that found no association between peer support and substance use, needs to be cited.

Response: Thank you for pointing out the typo, we have addressed it.

3. Authors were able to compare each of the significant factors that were associated with adolescent substance use in the area to existing literature. However, they failed to compare the prevalence of other recreational substances like khat and methamphetamines to that of existing literature. They only compared alcohol, cigarettes, and marijuana, but no discussion on the other recreational substances.

Response: Thank the reviewer this comment, we like to clarify. The overall prevalence of lifetime and current substance use was a composite measure of all substances and not specifically alcohol and cigarette smoking. The two substances, i.e., alcohol and cigarette were the commonly used among adolescents in this population which also agrees with the previous literature. In addition, the prevalence of other substances in this study had a combined prevalence of <5%.

Strengths and Limitations.

The study in 2011 by Mnyika et al., titled ‘Prevalence of and predictors of substance use among adolescents in rural villages of Moshi district, Tanzania’, assessed substance use amongst adolescents. Moshi District was included in this study. I suggest you revise this statement that says this study is the first to be done in the region. Consider saying it is the first that includes associated factors to substance use.

Response: We thank the reviewer for this comment, we have addressed and changed the statement. Which now reads “This study is one of the first in our setting to measure the prevalence and associated factors of substance use”

Conclusion.

The authors concluded that ‘The study’s prevalence of substance use is higher than the previous 2006 and 2015 Tanzania Global School-based Student Health Surveys’. This inference does not relate to the study results. The findings of the study did not result in this conclusion. I suggest the authors make concluding statements based on the findings of this study.

Response: We acknowledge the comments, we have addressed and changed the conclusion based on our findings.

Reference.

No.1 has the name of the main author missing from lists of authors.

Response: Thank you for pointing out the typo we have addressed it.

Ogundipe O, Amoo EO, Adeloye D. Substance use among adolescents in sub-Saharan Africa : A systematic review and meta-analysis. 2018;2016. doi:10.7196/SAJCH.2018.v12i2.1524

Minor Comments

1. In the Methods (p.6), you used “outcome”, “explanatory”, and “dependent” variables interchangeably. However, these terms are qualitatively different. In your case, it involves “substance use”, so I will suggest that you should use “dependent” variable throughout the paper.

Response: we acknowledge the comment, we have addressed it and changed the sub-heading to

“Study Variables.

12 Jul 2022

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

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25 Jul 2022

Reviewer comments:

1. My remaining point is that the discussion should focus on studies conducted in Africa and other low- and middle-income countries. As such, the authors should consider revising paragraph 3 of the discussion section that makes reference to studies conducted in the United States.

Response: Thank you for the good review and comment. We have edited paragraph three which states as follows: “However, previous studies in Zambia [27] and the United States[28, 29] found high substance use practice among adolescents 15 years and above. Likewise, analysis of GSHS data from six Asian low and middle-income countries revealed a higher risk of substance use (alcohol and smoking) among older compared to younger adolescents [30]. However, there are limited studies about the association between adolescent age and substance use in SSA.”

References

27. Siziya S, Muula AS, Besa C, Babaniyi O, Songolo P, Kankiza N, et al. Cannabis use and its socio-demographic correlates among in-school adolescents in Zambia. Ital J Pediatr. 2013;39: 1–5. doi:10.1186/1824-7288-39-13

28. Jones CM, Clayton HB, Deputy NP, Roehler DR, Ko JY. Prescription Opioid Misuse and Use of Alcohol and Other Substances Among High School Students — Youth Risk Behavior Survey , United States , 2019. 2020;69: 38–46.

29. Creamer MR, Jones SE, Gentzke AS, Jamal A, King BA. Tobacco Product Use Among High School Students — Youth Risk Data Source. 2020;69: 56–63.

Submitted filename: Response to Reviewers1.docx

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9 Aug 2022

Submitted filename: PONE-D-21-31212R2.pdf

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16 Aug 2022

1. My remaining point is that the discussion should focus on studies conducted in Africa and other low- and middle-income countries.

Response: Thank you for the good review and comment, we have edited paragraph we have edited paragraphs that did include cite studies from united states and other high income countries and focused more on sub-Saharan Africa ,low and middle income countries. The edited paragraph are will viewed on the document with track changes.

Submitted filename: Response to Reviewers1.docx

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23 Aug 2022

Prevalence of substance use and associated factors among secondary school adolescents in Kilimanjaro region, northern Tanzania

PONE-D-21-31212R3

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25 Aug 2022

PONE-D-21-31212R3

Prevalence of substance use and associated factors among secondary school adolescents in Kilimanjaro region, northern Tanzania

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