Cross-sectional examination of the association of co-occurring alcohol misuse and traumatic brain injury on mental health and conduct problems in adolescents in Ontario, Canada.

OBJECTIVE: This study describes the impact of traumatic brain injury (TBI) and hazardous drinking on mental health and behavioural issues among Ontario adolescents. In particular, we assessed the incremental co-occurrence of hazardous drinking with a history of TBI, in comparison to experiencing just one of these conditions.
METHODS: A cross-sectional subsample of 3130 Ontario adolescents attending grades 9-12, and aged 10-21 were surveyed in 2013 as a part of the Centre for Addiction and Mental Health's Ontario Student Drug Use and Health Survey. Recent (past year) and former (lifetime and excluding the last year) TBI were defined as trauma to the head that resulted in loss of consciousness for at least 5 min or overnight hospitalisation. Current hazardous drinking was derived using the Alcohol Use Disorders Identification Test (AUDIT).
RESULTS: An estimated 11.8% of Ontario adolescents (95% CI 10.1% to 13.8%) reported a history of former TBI and were not hazardous drinkers; 4.0% (95% CI 2.9% to 5.5%) reported recent TBI and were not hazardous drinkers; 13.7% (95% CI 12.3% to 15.3%) were hazardous drinkers who never had a TBI; 4.1% (95% CI 2.9% to 5.8%) had former TBI with co-occurring hazardous drinking; and 2.2% (95% CI 1.6% to 3.0%) had recent TBI with co-occurring hazardous drinking. Most odds increased significantly and were two to three times higher for reporting compromised mental health, violent and non-violent conduct behaviours, and reported victimisation for classifying as a hazardous drinker at the time of testing with co-occurring either former or recent TBI compared to classifying as not having either of these conditions. Adolescents classified as hazardous drinkers with former TBI had numerous and higher ORs for conduct behaviours than those with recent TBI.
CONCLUSIONS: Results emphasise the strong interplay between TBI and hazardous drinking and point to the need for integrating prevention efforts to reduce these conditions and their co-occurrence among adolescents. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.

This study shows that the emergence of hazardous drinking over the high school years may occur at an elevated rate among adolescents with traumatic brain injury (TBI).

This is the first time when temporarily interpretable patterns of association between hazardous drinking and history of TBI among adolescents were examined in the context of co-occurring mental health and problem behaviours in a population-based study.

Adolescents who classified as hazardous drinkers at the time of testing, with a former lifetime history of TBI (that occurred prior to past 12 months), had numerous and higher ORs for conduct behaviours than those with recent TBI (that occurred in the past 12 months).

Hazardous drinkers with recent TBI had more and higher ORs for most mental health behaviours than those with former TBI.

Possible bias related to self-report procedures and the preclusion of causal inferences due to the cross-sectional nature of the data are limitations of this study.

Introduction

Excessive drinking in adolescence can cause substantial harm to individuals and is associated with future alcohol-related problems.1–3 Drinking in adolescence is particularly risky because it is much more likely to be heavy and episodic (binge).4 5 Excessive drinking during adolescence, while the brain is still developing, can be a major cause of trauma, physical injuries, hospitalisation, prolonged disability and premature death.1–3 6 Alcohol contributes substantially to motor vehicle collisions, homicides, suicide, assault, sexual risk-taking and many other problems in Canada and the USA.7–16

Hazardous drinking is a contributor to and a consequence of traumatic brain injury (TBI).17 18 TBIs occur when a sudden trauma (hit or blow to the head) causes damage to the brain. An estimated 1 in 5 adolescents in Ontario has experienced TBI in their lifetime, and 1 in 18 has experienced it during the past 12 months.19 20 Hospitalisation data revealed that almost half of the individuals presenting with brain injuries were intoxicated on hospital admission, and among adolescents and adults who required inpatient rehabilitation post-TBI, over 60% were found to have had a history of alcohol or other drug misuse.21–23 Adolescents who had experienced one or more TBIs in their lifetime had odds twice as much to screen positive for current hazardous drinking or for reporting binge drinking in the past 12 months compared to those who never had a TBI.20

TBI and hazardous drinking are relatively common among adolescents4 19 20 and they have been linked with poor academic performance and mental health issues, including suicide, and increased violent and non-violent conduct behaviours.19 24–29 Several studies using imaging methods have noted negative additive effects of alcohol misuse and TBI, such as brain atrophy over time and reduced reaction times.30–32

However, no studies have compared the separate and joint effects of hazardous drinking and TBI in the general population or clinical samples of adolescents. Specifically, although previous research shows that hazardous drinking and a history of TBI are associated with harmful health outcomes, which include mental health and behavioural issues, the incremental impact of having both of these conditions is unknown.4 19–20 25–32 This study examines the association of history of TBI and hazardous drinking, separately and jointly, with past-year mental health and conduct behaviours in a large representative sample of high school adolescents, in Ontario.

Methods

Data were based on a subsample of 3264 students in grades 9–12 and were derived from the 2013 cycle of the Centre for Addition and Mental Health's (CAMH) Ontario Student Drug Use and Health Survey (OSDUHS), a biennially repeated cross-sectional probability survey of Ontario students enrolled in four provincially funded jurisdictions (Public vs Catholic; English vs French). In 2013, students were recruited from 198 schools and 671 classes dispersed province wide. Schools excluded from sampling were private, military and institutional schools. With these exclusions, our sample captures 92% of all Ontario children and adolescents aged 12–18.

Students completed self-administered, anonymous pen-and-paper questionnaires in their classrooms between November 2012 and June 2013. Participation rates were 61% for schools, 87% for classes and 63% for students. A comparison between high (≥70%) and low-responding classes showed no evidence of non-response bias for a number of health-related behaviours including TBI and the AUDIT.4 Students completed one of the two questionnaires (form A or form B) alternately distributed (ie, A, B, A) within each class. Although the TBI items were asked of all students using forms A and B, because the AUDIT screener was contained in form A only, the estimation samples were reduced from 6159 to 3264 students. A detailed description of the sampling design and survey procedures is web-available.4 33 The study was approved by the Research Ethics Committees of the CAMH, St. Michael's Hospital (SMH), participating Ontario Public and Catholic school boards and York University, which administered the surveys. All participants provided their assent in addition to parentally signed consent for those aged under 18.

Measures

Group membership categorisation

Our key analytical measure was derived from hazardous drinking and a history of TBI. Hazardous or harmful drinking was derived using the 10-item AUDIT screener, a well-validated instrument assessing drinking frequency, volume, heavy consumption and indicators of abuse and dependence due to alcohol.34 A cut-off score at or above 8 of 40 indicates a pattern of hazardous or harmful drinking.35

TBI was based on two questions that asked students if they ever had a blow or a hit to the head that rendered them unconscious for at least 5 min or resulted in their hospitalisation for at least one night. This criterion is also employed in diagnostic classification systems, including DSM-IV, and has previously been used in adolescent and adult studies.36 Students were then asked if they ever had such an injury in the 12 months prior (recent TBI) or in their lifetime, but not in the 12 months prior (former TBI). Our analytical variable was formed by cross-tabulating these two measures (hazardous drinking and TBI) to create a 6-class membership variable.

Mental health problems, conduct behaviours and covariates are summarised in table 1. The first set of analyses (tables 2–4) was based on the following six-level classifications. The baseline classification included adolescents who never had a TBI and screened negative for hazardous drinking on the AUDIT at the time of testing. The second classification included adolescents with former TBI (experienced sometimes during their lifetime but not in the past 12 months) who were not hazardous drinkers. Members in the third classification included adolescents with recent TBI (experienced in the past 12 months) who were not hazardous drinkers. The fourth classification included adolescents who screened positive on the AUDIT at the time of testing (hazardous drinkers), but did not report TBI (no former or recent). The fifth classification included current hazardous drinkers with co-occurring former TBI, and the sixth classification included hazardous drinkers with co-occurring recent TBI (no former TBI). The second set of analyses (table 5) was based on the following three-level classification: adolescents who did not report a TBI (former or recent) nor did they screen positive on the AUDIT; adolescents who reported either former or recent TBI, or who screened positive on the AUDIT; and adolescents who screened positive on the AUDIT and also reported either former or recent TBI.

Table 1

Covariates and predictors included in the analysis

Variable	Definition
Sex—covariate	Male, female
Grade—covariate	Four categories: 9th, 10th, 11th, 12th
Mental health measures
Psychological distress	Moderate to high vs low psychological distress in the past 4 weeks GHQ25
Used prescribed medication to reduce anxiety, depression or both	Taking prescribed medication in the past 12 months for anxiety, depression or both (yes=1, 0 otherwise)
Suicidal ideation	Seriously considered suicide in the past 12 months (yes=1, 0 otherwise)
Suicide attempt	Attempted to commit suicide in the past 12 months (yes=1, 0 otherwise)
Called a crisis or help line in past 12 months	Called a youth crisis or help line in past 12 months for help (yes=1; 0 otherwise)
Used prescribed medication to treat ADHD	Use of prescribed medication in the past 12 months to treat ADHD (yes=1, 0 otherwise)
Self-rated mental health status	Reported excellent/good mental health vs fair or poor mental health (yes=1; 0 otherwise)
Self-rated health status	Reporting excellent/good health vs fair or poor health in general (yes=1; 0 otherwise)
Violent and non-violent conduct behaviours (perpetrator or victim)
Drove a car without the owner's permission	Taken the car for a ride without the owner's permission at least once in the past 12 months (yes=1; 0 otherwise)
Damage to property	Damaged something on purpose that did not belong to you at least once in past 12 months (yes=1; 0 otherwise)
Sold marijuana or hashish at school	Sold marijuana or hashish at least once in the past 12 months (yes=1; 0 otherwise)
Stealing (things worth 50$ or less)	Taken things worth $50 or less at least once in the past 12 months (yes=1; 0 otherwise)
Stealing (things worth more than 50$)	Taken things worth $50 or more at least once in the past 12 months (yes=1; 0 otherwise)
Physical violence (in purpose)	Beat up, hurt anyone on purpose at least once in the past 12 months (yes=1; 0 otherwise)
Physical violence at school	Engaged in a physical fight on school property at least once in the past 12 months (yes=1; 0 otherwise)
Breaking into property	Broken into a locked building other than one's own at least once in the past 12 months (yes=1; 0 otherwise)
Possession of a weapon (eg, gun and knife) on school property	Carried a weapon such as a gun or a knife at least once in the past 12 months (yes=1; 0 otherwise)
Running from home	Ran away from home in the past 12 months (yes=1; 0 otherwise)
Set fire	Set something on fire you were not supposed to at least once in the past 12 months (yes=1; 0 otherwise)
Bullied others	Bullied others at school at least once in the past 12 months (yes=1; 0 otherwise)
Being threatened with a gun or weapon at school (Victim)	Was threatened with a gun or a weapon on school property in the past 12 months (yes=1; 0 otherwise)
Being bullied at school (Victim)	Was bullied at school at least once in the past 12 months (yes=1; 0 otherwise)
Being bullied through the internet (Victim)	Was bullied through the internet at least once in the past 12 months (yes=1; 0 otherwise)

ADHD, Attention deficit hyperactivity disorder; GHQ, General Health Questionnaire

Table 2

Descriptive analyses predicting membership classification: TBI former (lifetime but not past 12 months; no current hazardous drinking), TBI recent (past 12 months; no current hazardous drinking), hazardous drinking (never had TBI), former TBI with co-occurring hazardous drinking (no recent TBI), recent TBI with co-occurring hazardous drinking and base category (no TBI or hazardous drinking) by demographics, among adolescents in grades 9–12, Ontario, Canada, 2013, n=3130

	Base category% (95% CI)OR (95% CI)n=2082	Former TBI (no hazardous drinking)% (95% CI)OR (95% CI)n=367	Recent TBI (no hazardous drinking)% (95% CI)OR (95% CI)n=104	Hazardous drinking (no TBI)% (95% CI)OR (95% CI)n=390	Former TBI and hazardous drinking% (95% CI)OR (95% CI)n=117	Recent TBI and hazardous drinking% (95% CI)OR (95% CI)n=70
Sex	F(5,94)=1.08
Male	62.0 (57.4 to 66.5)	12.6 (10.0 to 15.8)	4.4 (3.0 to 6.6)	13.5 (11.6 to 15.7)	5.1 (3.1 to 8.4)	2.3 (1.4 to 3.8)
	1.00 (Ref.)	1.23 (0.85 to 1.78)	1.31 (0.67 to 2.53)	1.03 (0.78 to 1.37)	1.79 (0.93 to 3.44)	1.16 (0.57 to 2.32)
	n=864	n=187	n=51	n=155	n=60	n=34
Female (Ref.)	66.3 (62.5 to 69.8)	11.0 (8.8 to 13.6)	3.6 (2.2 to 6.0)	13.9 (11.7 to 16.6)	3.1 (2.1 to 4.4)	2.1 (1.4 to 3.1)
	n=1218	n=180	n=53	n=235	n=57	n=36
Grade	F(15,84)=14.37***
12	72.1 (68.6 to 75.3)	14.8 (11.8 to 18.4)	6.5 (4.4 to 9.5)	4.8 (3.2 to 7.1)	0.8 (0.3 to 1.9)	1.1 (0.5 to 2.5)
	1.00 (Ref.)	0.84 (0.52 to 1.34)	0.84 (0.39 to 1.79)	6.35 (4.16 to 9.69)***	11.75 (4.03 to 34.27)***	3.07 (1.16 to 8.15)**
	n=458	n=60	n=22	n=162	n=46	n=24
11	71.1 (65.9 to 75.7)	13.3 (10.0 to 17.4)	2.4 (1.2 to 4.8)	8.0 (4.9 to 12.8)	2.5 (1.3 to 4.9)	2.8 (1.4 to 5.5)
	1.00 (Ref.)	0.85 (0.55 to 1.30)	0.58 (0.32 to 1.04)	3.58 (1.98 to 6.46)***	7.88 (2.96 to 20.95)***	2.47 (0.74 to 8.24)
	n=518	n=88	n=22	n=125	n=35	n=21
10	63.2 (57.4 to 68.6)	11.0 (8.2 to 14.5)	3.3 (1.9 to 5.7)	15 (11.1 to 19.9)	5.3 (3.7 to 7.4)	2.4 (1.0 to 5.6)
	1.00 (Ref.)	0.91 (0.65 to 1.28)	0.37 (0.18 to 0.78)	1.69 (0.87 to 3.39)	3.37 (1.06 to 10.76)*	2.57 (0.84 to 7.89)
	n=548	n=110	n=24	n=63	n=22	n=14
9 (Ref.)	54.4 (48.9 to 59.7)	9.4 (6.9 to 12.6)	4.1 (2.2 to 7.6)	22.9 (19.6 to 26.5)	6.7 (4.2 to 10.7)	2.5 (1.6 to 3.8)
	n=558	n=109	n=36	n=40	n=14	n=11

TBI, traumatic brain injury.

* P < 0.05; ** P < 0.01; *** P < 0.001.

Table 3

Multinomial logistic regression analyses predicting membership classifications: former TBI (lifetime but not in the past 12 months; no current hazardous drinking), recent TBI (in the past 12 months; no current hazardous drinking), hazardous drinking (never had TBI), former TBI with co-occurring hazardous drinking (no recent TBI), recent TBI with co-occurring hazardous drinking and base category (Ref.; no TBI or hazardous drinking) by mental health measures among adolescents in grades 9–12, Ontario, Canada, 2013, n=3130

	Former TBI (n=367) vs base category (n=2082)OR (95% CI)aOR (95% CI)	Recent TBI (n=104) vs base category (n=2082)OR (95% CI)aOR (95% CI)	Hazardous drinking (n=390) vs base category (n=2082)OR (95% CI)aOR (95% CI)	Former TBI and hazardous drinking (n=117) vs base category (n=2082)OR (95% CI)aOR (95% CI)	Recent TBI and hazardous drinking (n=70) vs base category (n=2082)OR (95% CI)aOR (95% CI)
Moderate to high levels of psychological distress
F(5,94)=7.29***	1.17 (0.80 to 1.73)	1.15 (0.54 to 2.43)	1.49 (1.17 to 1.90)**	3.10 (1.67 to 5.75)***	2.14 (1.07 to 4.30)*
F(15,84)=9.80***	1.25 (0.87 to 1.81)	1.24 (0.64 to 2.40)	1.65 (1.29 to 2.13)***	4.06 (2.21 to 7.44)***	2.36 (1.11 to 5.02)*
Prescription medication for anxiety, depression or both in the past 12 months
F(5,94)=6.36***	2.26 (1.08 to 4.73)*	1.90 (0.65 to 5.55)	2.11 (1.13 to 3.96)*	6.15 (2.75 to 13.77)***	6.24 (2.73 to 14.28)***
F(15,84)=11.80***	2.44 (1.18 to 0.07)*	2.08 (0.73 to 5.86)	1.74 (0.81 to 3.73)	6.02 (2.59 to 13.0)***	6.17 (2.64 to 14.42)***
Did you contemplate attempt suicide in the past 12 months?
F(5,90)=7.49***	1.65 (1.12 to 2.45)*	1.98 (0.88 to 4.49)	1.88 (1.31 to 2.70)**	2.71 (1.29 to 5.69)**	4.45 (1.90 to 10.42)**
F(15,80)=11.80***	1.74 (1.17 to 2.57)**	2.11 (0.99 to 4.47)	2.17 (1.50 to 3.13)***	3.48 (1.62 to 7.48)**	4.96 (2.07 to 11.90) ***
Did you actually attempt suicide in the past 12 months?
F(5,90)=15.93***	4.43 (2.27 to 8.64)***	8.14 (2.68 to 24.73)***	5.03 (2.64 to 9.58)***	6.36 (2.11 to 19.14)**	24.77 (9.10 to 67.42)***
F(15,80)=14.29***	4.81 (2.48 to 9.35)***	9.14 (3.22 to 25.93)***	6.45 (3.09 to 13.48)***	9.70 (3.37 to 27.96)***	31.23 (10.29 to 94.82)***
Called a child crisis or help line in the past 12 months
F(5,94)=5.34***	2.05 (1.49 to 6.26)**	0.32 (0.08 to 1.23)	2.12 (1.01 to 4.43)*	3.20 (1.05 to 9.70)*	5.49 (2.0 to 15.08)**
F(15,84)=9.77***	3.26 (1.58 to 6.74)**	0.34 (0.09 to 1.34)	2.11 (0.99 to 4.46)	3.75 (1.24 to 11.33)*	5.80 (2.13 to 15.80)**
Used prescribed medication to treat ADHD in the past 12 months
F(5,94)=4.10**	2.99 (1.32 to 6.79)**	5.39 (0.97 to 30.05)	2.86 (1.45 to 5.62)**	5.23 (1.90 to 14.37)**	7.29 (1.83 to 29.01)**
F(15,84)=11.32***	2.88 (1.25 to 6.59)*	5.12 (0.93 to 28.14)	2.99 (1.47 to 6.06)**	5.00 (1.74 to 14.41)**	7.33 (1.90 to 28.30)**
Reporting fair or poor mental health in general
F(5,94)=5.18***	1.53 (1.03 to 2.28)*	1.30 (0.58 to 2.87)	1.31 (0.98 to 1.77)	3.37 (1.71 to 6.64)**	2.85 (1.42 to 5.74)**
F(15,84)=8.79***	1.61 (1.10 to 2.36)*	1.38 (0.68 to 2.80)	1.40 (1.02 to 1.91)*	3.93 (2.03 to 7.61)***	3.07 (1.46 to 6.44)**
Reporting fair or poor health in general
F(5,94)=0.20	0.98 (0.59 to 1.64)	1.10 (0.38 to 3.17)	1.15 (0.63 to 2.10)	1.40 (0.61 to 3.20)	1.25 (0.33 to 4.65)
F(15,84)=10.83***	0.99 (0.59 to 1.66)	1.11 (0.39 to 3.18)	1.12 (0.62 to 2.04)	1.40 (0.63 to 3.12)	1.23 (0.34 to 4.48)

F—design adjusted Wald F tests; ORs and adjusted ORs (aORs) were calculated using logistic regression. aORs were evaluated while holding fixed values of the complexity of the design, sex and grade.

***p<0.001; **p<0.01; *p<0.05.

TBI, traumatic brain injury.

Table 4

Multinomial logistic regression analyses predicting membership classifications: former TBI (lifetime but not in the past 12 months; no current hazardous drinking), recent TBI (in the past 12 months; no current hazardous drinking), hazardous drinking (never had TBI), former TBI with co-occurring hazardous drinking (no recent TBI), recent TBI with co-occurring hazardous drinking and base category (Ref.; no TBI or hazardous drinking) by conduct behaviours among adolescents in grades 9–12, Ontario, Canada, 2013, n=3130

	Former TBI (n=367) vs base category (n=2082)OR (95% CI)aOR (95% CI)	Recent TBI (n=104) vs base category (n=2082)OR (95% CI)aOR (95% CI)	Hazardous drinking (n=390) vs base category (n=2082)OR (95% CI)aOR (95% CI)	Former TBI and hazardous drinking (n=117) vs base category (n=2082)OR (95% CI)aOR (95% CI)	Recent TBI and hazardous drinking (n=70) vs base category (n=2082)OR (95% CI)aOR (95% CI)
Taken the car** for a ride without the owner's permission
F(5,94)=26.32***	2.14 (0.95 to 4.82)	4.29 (1.35 to 13.65)*	6.48 (4.02 to 10.43)***	17.92 (9.57 to 33.55)***	3.17 (0.97 to 10.39)
F(15,84)=14.52***	2.17 (0.97 to 4.88)	4.27 (1.33 to 13.69)*	5.61 (3.53 to 8.94)***	15.15 (7.77 to 29.56)***	2.93 (0.87 to 9.93)
Damaged something on purpose
F(5,94)=14.57***	1.46 (0.89 to 2.38)	6.21 (2.76 to 13.98)***	2.72 (1.65 to 4.49)***	5.50 (2.50 to 12.07)***	9.29 (4.44 to 19.44)***
F(15,84)=21.56***	1.42 (0.87 to 2.33)	6.13 (2.67 to 14.06)***	3.14 (1.86 to 5.29)***	6.16 (2.65 to 14.31)***	9.98 (4.65 to 21.44)***
Sold marijuana or hashish
F(5,94)=31.48***	2.51 (1.26 to 5.02)*	10.16 (3.22 to 32.06)***	12.11 (6.86 to 21.36)***	29.29 (16.63 to 51.58)***	8.82 (3.25 to 23.97)***
F(15,84)=18.00***	2.41 (1.74 to 4.95)*	9.80 (3.21 to 29.94)***	13.35 (6.37 to 27.98)***	29.71 (14.88 to 59.31)***	9.02 (2.86 to 28.45)***
Taken things worth $50 or less
F(5,94)=19.02***	2.07 (1.31 to 3.25)**	2.18 (1.06 to 4.45)*	5.17 (3.18 to 8.39)***	6.92 (4.02 to 11.91)***	2.59 (0.78 to 8.54)
F(5,84)=20.06***	2.04 (1.30 to 3.22)**	2.12 (1.02 to 4.12)*	5.31 (3.43 to 8.22)***	6.69 (3.86 to 11.59)***	2.57 (0.78 to 8.49)
Stealing more than $50
F(5,94)=11.28***	1.62 (0.59 to 4.47)	2.83 (0.86 to 9.33)	7.77 (3.39 to 17.82)***	15.17 (5.93 to 38.84)***	8.13 (2.41 to 27/36)**
F(15,84)=13.97***	1.62 (0.58 to 4.54)	2.75 (0.83 to 9.12)	7.05 (2.96 to 16.81)***	12.88 (4.70 to 35.30)***	7.61 (2.24 to 25.87)**
Beat up, hurt anyone on purpose
F(5,94)=18.08***	2.40 (1.22 to 4.75)*	4.34 (1.84 to 10.20)**	4.97 (2.71 to 9.10)***	9.61 (4.93 to 18.73)***	8.64 (2.98 to 25.04)***
F(15,84)=17.64***	2.31 (1.15 to 4.64)*	4.18 (1.77 to 9.84) **	5.98 (3.16 to 11.32)***	11.06 (5.26 to 23.24)***	9.40 (3.19 to 27.66) ***
Broken into a locked building other than one's own
F(5,94)=20.49***	0.48 (0.18 to 1.30)	1.92 (0.59 to 6.26)	4.81 (2.31 to 10.05)***	8.70 (3.83 to 19.78)***	9.43 (2.84 to 31.34)***
F(15,84)=10.72***	0.48 (0.18 to 1.26)	1.85 (2.08 to 6.46)	4.79 (2.08 to 11.05)***	8.01 (3.12 to 20.62)***	9.26 (2.59 to 33.13)***
Carried a weapon such** as a gun or a knife
F(5,94)=13.767***	5.13 (2.81 to 9.35)***	6.66 (2.75 to 16.10)***	5.67 (2.82 to 11.38)***	9.99 (4.85 to 20.57)***	9.21 (3.57 to 23.74)***
F(1584)=29.00***	4.92 (2.69 to 8.97)***	6.40 (2.35 to 17.43)***	7.67 (3.95 to 14.90)***	12.73 (5.79 to 27.99)***	10.71(4.06 to 28.20)***
Run away from home
F(5,94)=13.67***	1.76 (0.99 to 3.13)	3.67 (2.30 to 5.84)***	4.16 (2.56 to 6.77)***	4.85 (2.01 to 11.73)**	4.49 (1.57 to 12.86)**
F(15,84)=12.60***	1.78 (0.99 to 3.16)	3.78 (2.44 to 5.86)***	4.55 (2.82 to 7.33)***	5.79 (2.16 to 15.52)**	4.74 (1.59 to 14.17)**
Set fire
F(5,94)=14.58***	1.47 (0.94 to 2.29)	3.04 (1.26 to 7.35)*	4.00 (2.69 to 5.92)***	6.07 (3.03 to 12.16)***	3.54 (1.36 to 9.20)*
F(15,84)=24.63***	1.40 (0.92 to 2.14)	2.96 (1.17 to 7.46)*	5.34 (3.41 to 8.37)***	7.88 (3.77 to 16.47)***	4.02 (1.59 to 10.15)**
In a physical fight on school property
F(5,94)=6.65***	2.36 (1.42 to 3.92)**	6.59 (2.77 to 15.68)***	1.98 (0.96 to 4.11)	4.91 (2.26 to 10.68)***	4.21 (1.55 to 11.46)**
F(15,84)=15.92***	2.25 (1.38 to 3.66)**	6.78 (2.70 to 17.01)***	2.50 (1.14 to 5.49)*	5.62 (2.28 to 13.83)***	4.77 (1.77 to 12.86)**
Bullied others at school
F(5,94)=10.05***	1.52 (1.00 to 2.32)	1.56 (0.54 to 4.50)	2.12 (1.40 to 3.20)***	4.54 (2.62 to 7.85)***	3.81 (1.85 to 7.83)***
F(5,84)=14.74***	1.48 (0.98 to 2.25)	1.52 (0.52 to 4.49)	2.50 (1.61 to 3.89)***	5.24 (2.93 to 9.37)***	4.11 (2.05 to 8.26)***
Was threatened with a gun or a weapon (VICTIM)
F(5,94)=9.20***	2.72 (1.42 to 5.24)**	7.35 (2.39 to 22.60)**	2.48 (1.27 to 5.29)*	7.19 (2.18 to 16.25)***	6.72 (2.64 to 17.16)***
F(5,84)=17.53***	2.61 (1.37 to 4.95)**	7.12 (2.35 to 21.55)**	2.90 (1.29 to 6.52)*	7.97 (3.25 to 19.55)***	7.20 (2.87 to 18.08)***
Been bullied at school (VICTIM)
F(5,94)=3.33**	1.63 (1.15 to 2.31)*	2.04 (1.06 to 3.95)*	1.24 (0.88 to 1.74)	2.07 (1.00 to 4.30)	2.44 (1.20 to 4.95)*
F(5,84)=9.41***	1.63 (1.16 to 2.28)*	2.08 (1.12 to 3.87)*	1.52 (1.08 to 2.15)*	2.77 (1.34 to 5.71)**	2.77 (1.37 to 5.57)**
Been bullied through the internet (VICTIM)
F(5,94)=6.73***	1.55 (1.03 to 2.34)*	3.22 (1.47 to 7.10)**	1.48 (0.99 to 2.22)	3.29 (1.80 to 6.02)***	2.64 (1.22 to 5.70)*
F(5,84)=12.34***	1.56 (1.03 to 2.38)*	3.36 (1.48 to 7.64)**	1.76 (1.18 to 2.64)**	4.17 (2.18 to 7.98)***	2.94 (1.20 to 6.64)*

F—design adjusted Wald F tests; ORs and adjusted ORs (aORs) were calculated using logistic regression.

aORs were evaluated while holding fixed values of the complexity of the design, sex and grade.

***p<0.001; ** p<0.01; *p<0.05.

TBI, traumatic brain injury.

Table 5

Multinomial logistic regression analyses predicting membership classifications by history of TBI and hazardous drinking: either history of TBI or hazardous drinking, separately; no history of TBI or hazardous drinking; co-occurring history of TBI with current hazardous drinking for mental health and conduct behaviour measures, n=3130

	No history of TBI or hazardous drinking (n=2082) vs history of TBI or hazardous drinking (n=881)OR (95% CI)aOR (95% CI)	History of TBI with hazardous drinking (n=187) vs history of TBI or hazardous drinking (n=881)OR (95% CI)aOR (95% CI)
Mental health measures
Moderate to high levels vs low levels of psychological distress
F(2,352)=24.11***	0.68 (0.55 to 0.85)***	2.26 (1.51 to 3.39)***
F(2,355)=24.27***	0.66 (0.53 to 0.82)***	2.42 (1.16 to 3.63)***
Past 12 months prescription medication for anxiety, depression or both
F(2,181)=6.36***	0.46 (0.26 to 0.84)***	2.89 (1.63 to 5.12)***
F(2,180)=12.60***	0.49 (0.26 to 0.92)***	2.98 (1.68 to 5.29)***
Past 12 months did you contemplate attempt suicide
F(2,339)=17.82***	0.57 (0.44 to 0.75)***	1.95 (1.19 to 3.17)*
F(2,333)=19.99***	0.53 (0.40 to 0.70)***	2.17 (1.21 to 3.58)***
Past 12 months did you actually attempt suicide
F(2,327)=25.34***	0.26 (0.17 to 0.41)***	2.39 (1.21 to 4.72)***
F(2,306)=28.17***	0.23 (0.15 to 0.35)***	2.95 (1.39 to 6.26)***
Called a child crisis or help line in past 12 months
F(2,355)=10.98***	0.34 (0.28 to 0.68)***	1.65 (0.82 to 3.32)
F(2,349)=12.32***	0.40 (0.26 to 0.62)***	1.81 (0.86 to 3.79)
Past 12 months used prescribed medication to treat ADHD
F(2,346)=12.11***	0.32 (0.18 to 0.58)***	2.01 (0.85 to 4.72)
F(2,346)=10.54***	0.32 (0.18 to 0.57)***	2.04 (0.82 to 5.05)
Reporting fair or poor mental health in general vs excellent/good mental health
F(2,318)=21.10***	0.63 (0.51 to 0.68)***	2.33 (1.42 to 3.84)***
F(2,312)=22.03***	0.61 (0.50 to 0.75)***	2.44 (1.48 to 4.03)***
Reporting fair or poor health in general vs excellent/good health
F(2,302)=0.91	0.80 (0.51 to 1.24)	1.15 (0.55 to 2.38)
F(2,336)=0.81	0.80 (0.50 to 1.28)	1.16 (0.57 to 2.34)
Conduct behaviours
Taken a car for a ride without the owner's permission
F(2,320)=46.22***	0.21 (0.13 to 0.34)***	3.04 (1.95 to 4.76)***
F(2,329)=31.17***	0.26 (0.16 to 0.41)***	2.49 (1.54 to 4.03)***
Damaged something on purpose
F(2,352)=33.68***	0.42 (0.30 to 0.59)***	2.85 (1.75 to 4.65)***
F(2,348)=32.07***	0.41 (0.29 to 0.58)***	3.00 (1.78 to 5.08)***
Sold marijuana or hashish
F(2,329)=43.92***	0.14 (0.08 to 0.26)*	3.11 (1.78 to 5.46)***
F(2,340)=34.01***	0.17 (0.09 to 0.30)*	2.76 (1.52 to 5.00)***
Taken things worth $50 or less
F(2,355)=48.78***	0.29 (0.22 to 0.39)***	1.76 (1.12 to 2.76)***
F(2,350)=41.12***	0.32 (0.24 to 0.42)***	1.59 (0.99 to 2.54)
Stealing more than $50
F(2,356)=24.93***	0.22 (0.12 to 0.42)***	3.20 (1.59 to 6.44)***
F(2,356)=18.19***	0.26 (0.14 to 0.49)***	2.71 (1.31 to 5.62)***
Beat up, hurt anyone in purpose
F(2.253)=35.61***	0.29 (0.19 to 0.433)***	2.54 (1.46 to 4.41)***
F(2,253)=33.70***	0.28 (0.18 to 0.42)***	2.76 (1.54 to 4.95)***
Broken into a locked building other than one's own
F(2,355)=25.58***	0.33 (0.17 to 0.64)***	4.41 (2.19 to 8.89)***
F(2,355)=15.39***	0.38 (0.19 to 0.75)***	1.85 (1.18 to 2.53)***
Carried a weapon such as a gun or a knife
F(2,326)=32.61***	0.21 (0.12 to 0.35)***	2.08 (1.16 to 3.74)***
F(2,334)=33.92***	0.20 (0.12 to 0.33)***	2.34 (1.23 to 4.44)***
Run away from home
F(2,326)=22.81***	0.33 (0.24 to 0.46)***	1.72 (0.89 to 3.34)
F(2,307)=1815***	0.33 (0.24 to 0.47)***	1.75 (0.84 to 3.66)
Set fire
F(2,340)=22.86***	0.43 (0.30 to 0.62)***	1.95 (1.22 to 3.10)***
F(2,345)=27.65***	0.41 (0.29 to 0.58)***	2.17 (1.35 to 3.49)***
In a physical fight on school property
F(2,349)=18.53***	0.46 (0.32 to 0.65)***	1.77 (1.07 to 2.94)*
F(2,343)=25.03***	0.39 (0.28 to 0.54)***	2.11 (1.21 to 3.71)**
Bullied others at school
F(2,354)=23.23**	0.64 (0.50 to 0.82)***	2.55 (1.63 to 3.97)***
F(2,354)=26.61***	0.61 (0.48 to 0.79)***	2.79 (1.77 to 4.39)***
Was threatened with a gun or a weapon (VICTIM)
F(2,329)=16.37***	0.39 (0.25 to 0.61)***	2.25 (1.06 to 4.77)*
F(2,325)=18.27***	0.37 (0.24 to 0.57)***	2.45 (1.12 to 5.36)**
Was bullied at school (VICTIM)
F(2,346)=7.97***	0.67 (0.54 to 0.84)***	1.31 (0.79 to 2.18)
F(2,344)=16.93***	0.57 (0.45 to 0.71)***	1.65 (1.01 to 2.73)
Was bullied through the internet (VICTIM)
F(2,354)=23.23**	0.60 (0.46 to 0.78)***	1.71 (1.02 to 2.88)*
F(2,347)=18.66***	0.53 (0.41 to 0.69)***	1.99 (1.16 to 3.43)***

F—design adjusted Wald F tests; ORs and adjusted ORs (aORs) were calculated using logistic regression. aORs were evaluated while holding fixed values of the complexity of the design, sex and grade.

***p<0.001; **p<0.01; *p<0.05.

TBI, traumatic brain injury.

Analysis

Data derived from complex surveys using stratification and clustering fail the assumption of independent observations and thus underestimate variances (and, in doing, they overstate significance levels resulting in false-positive inferences). We therefore employed design-based estimation methods to accommodate such violations. Our subsample analyses utilised a complex sample design with 20 strata (region by school level) and 198 primary sampling units (high schools). The variance of our analyses was estimated by Taylor Series Linearization executed in the Complex Sample module in SPSS V.23.0 (SPSS, 2015). In addition to strata and clusters, our analyses employed case weights that factored inclusion probabilities, non-response and poststratification adjustments. We applied multinomial logistic regressions to assess the association between TBI–AUDIT classes and 8 mental health and 15 conduct behaviours, with and without holding sex and grade constant, against p<0.05 (two-tailed). The results are based on ‘valid’ responses (n's); missing data (ie, ‘don't know’ responses and refusals) were excluded. Listwise deletion reduced the estimation sample from 3264 to 3130.

Results

An estimated 11.8% (95% CI 10.1% to 13.8%) of Ontario adolescents reported former TBI, 4.0% (95% CI 2.9% to 5.5%) reported recent TBI, 13.7% (95% CI 12.3% to 15.3%) were identified as hazardous drinkers, 4.1% (95% CI 2.9% to 5.8%) reported former TBI with co-occurring hazardous drinking, 2.2% (95% CI 1.6% to 3.0%) reported recent TBI with co-occurring hazardous drinking and 64.1% (95% CI 60.9% to 67.2%) were individuals who never had a TBI and scored negative on the AUDIT.

Demographic characteristics

Table 2 presents the demographic characteristics of the sample by TBI–AUDIT classifications. ORs were similar for males versus females on all six TBI–AUDIT classifications, while grade level in high school significantly predicted TBI–AUDIT classification. Among adolescents in grade 12, ORs were 6 times significantly higher for hazardous drinking, nearly 12 times higher for reporting former TBI with co-occurring hazardous drinking and 3 times higher for reporting recent TBI with co-occurring hazardous drinking, compared to baseline classification (neither conditions). Adolescents in grade 11 had odds nearly four times higher for hazardous drinking and nearly eight times higher for reporting former TBI with co-occurring hazardous drinking, compared to baseline classification. Among students in grade 10, the odds were three times higher for reporting former TBI with co-occurring hazardous drinking, compared to baseline classification.

Associations between TBI, problem drinking and recent mental health problems

Table 3 summarises the results of multinomial regression analyses fitting TBI–AUDIT classification by mental health conditions. For five of the eight mental health conditions, adjusted ORs associated with screening positive for hazardous drinking, without a co-occurring history of TBI, were statistically significant, compared to individuals in the baseline classification (neither conditions), and ranged from 1.40 to 6.45. For six of the eight mental health conditions assessed, adjusted ORs associated with former TBI, without co-occurring hazardous drinking, were statistically significant and ranged from 1.61 to 4.81. Only one of the eight mental health conditions assessed had significant adjusted ORs associated with recent TBI. Adjusted odds were 9.14 times higher for suicide attempt among adolescents with recent TBI compared to those with no history of TBI that screened negative for hazardous drinking.

With the addition of hazardous drinking to former TBI, the adjusted ORs associated with seven of eight mental health conditions assessed increased, compared to either classification alone, and were statistically significant ranging from 3.75 to 9.70. With the addition of hazardous drinking to recent TBI, the adjusted ORs associated with seven of the eight mental health conditions assessed increased, compared to either classification alone, and were statistically significant, ranging from 2.36 to 31.23. Self-rated general health was not statistically significantly associated with any of the TBI–AUDIT classifications.

Associations between TBI, problem drinking and recent conduct behavioural issues

Table 4 presents the results of multinomial regression predicting membership in the 6 TBI–AUDIT classifications by 15 conduct behaviours. For 5 of 12 perpetrator behaviours, statistically significant adjusted ORs were associated with former TBI compared to the baseline classification (neither conditions). With the addition of hazardous drinking to former TBI, the adjusted ORs associated with perpetrator reports of conduct behaviour were higher and statistically significant on all 12 measures, and were ranged between 5.24 and 29.71. For all of the conduct behaviours in which the adolescent reported being a victim, adjusted ORs associated with former TBI, without hazardous drinking, were statistically significant and ranged between 1.56 and 2.61. With the addition of hazardous drinking to former TBI, compared to the baseline classification, the adjusted ORs associated with all three conduct behaviour victimisation variables were statistically significant and ranged between 3.17 and 7.97.

For 9 of the 12 perpetrator-type conduct behaviours assessed, statistically significant adjusted ORs associated with recent TBI classification were observed. For all three victimisation conduct behaviours associated with recent TBI, adjusted ORs were significant. With the addition of current hazardous drinking to recent TBI, the adjusted ORs associated with perpetrator reports of conduct behaviour were statistically significant on 10 of the 13 measures compared to individuals in the baseline membership class (neither conditions). With the addition of hazardous drinking to recent TBI, compared to the baseline classification, the adjusted ORs associated with all three measures of conduct behaviour victimisation were statistically significant. The adjusted ORs of perpetration of conduct behaviours associated with hazardous drinking were statistically significant for all of the 12 measures.

Comparing the individual versus combined effects of TBI and problem drinking

Table 5 summarises analyses designed to highlight the incremental impact of experiencing co-occurring TBI and hazardous drinking compared to either condition by itself (referent). The analysis also included those with no history of TBI or hazardous drinking. Comparisons between the three groups revealed significantly higher adjusted ORs that ranged between 2.17 and 2.98 on all six mental health measures for students who experienced both conditions in comparison to those who experienced one. Students who reported both conditions (TBI and co-occurring hazardous drinking) had significantly higher adjusted odds of mental health problem indicators on measures of psychological distress, use of medication for depression or anxiety, contemplating suicide in the past 12 months, attempting suicide in the past 12 months and fair or poor self-reported mental health. The two groups did not differ on three mental health measures (called a crisis or help line, used prescribed medication for ADHD, reporting fair or poor general health). Compared to students who experienced one condition (had a history of TBI or screened positive for hazardous drinking), students reporting neither had significantly lower adjusted odds of mental health problem indicators on seven of the eight measures. The only exception was that the groups did not differ on self-reported general health.

For measures of perpetration (table 5), students who reported co-occurring TBI and hazardous drinking had significantly higher adjusted odds of reporting taking a car without permission, damaging property, selling cannabis, stealing more than $50, beating up or hurting someone, breaking into a locked building, carrying a weapon, setting a fire, fighting on school property and bullying others at school. The two groups did not differ on the adjusted odds of taking things worth less than $50 and running away from home. Compared to the group reporting one condition (TBI or hazardous drinking), those reporting neither had significantly lower adjusted odds on all measures of perpetration. For measures of victimisation, those reporting both conditions (TBI and co-occurring hazardous drinking) had significantly higher adjusted odds of being threatened with a weapon and being bullied on the internet, but did not differ on odds of being bullied at school. Those reporting neither condition (never had TBI and failed to score positive for hazardous drinking), compared to the group reporting one of the two conditions (TBI or hazardous drinking), had significantly lower adjusted odds on all three measures of victimisation.

Discussion

In this population of Ontario high school students, one in eight reported former TBI (incurred during lifetime but not in the past 12 months) and were not current drinkers; 1 in 25 were identified as hazardous drinkers with co-occurring recent TBI; 1 in 7 were identified as hazardous drinkers and had no history of TBI; 1 in 24 were identified as hazardous drinkers with co-occurring history of former TBI and 1 in 45 were identified as hazardous drinkers with co-occurring recent TBI. In our sample, group membership did not vary by sex, but did vary by age, as measured by school grade. Significant ORs emerged for hazardous drinking with a co-occurring history of former TBI among grade 10, 11 and 12 students compared to those in grade 9. ORs were three times higher for hazardous drinking with co-occurring recent TBI among grade 12 compared to grade 9 students. ORs were 3.5 and 6 times higher for hazardous drinking among grade 11 and 12 students, respectively, compared to grade 9 students. These differences mirror patterns of such differences in the adolescent population reported previously.4 18–21 33 36 These results show the emergence of hazardous drinking over the high school years and suggest that this emergence may occur at an elevated rate among those with former and current TBI.

Since we were unable to find previous studies examining the co-occurrence of hazardous drinking and TBI in a representative sample of adolescents, there is no study to compare our estimates. However, adult studies have shown that among individuals currently in rehabilitation for substance abuse, the rates of co-occurring alcohol problems with a history of TBI ranged between 38% and 63%.37 38 We found that of all students screening positive at the time of testing for hazardous drinking, 32.4% also reported a history of TBI, which approaches the range observed in these adult studies and confirms the notable existence of the TBI–alcohol co-occurrence.37 38 Co-occurring recent TBIs with hazardous drinking were associated with higher ORs, overall, for mental health issues, whereas former TBIs with hazardous drinking were associated with higher ORs, overall, for conduct behaviour compared to no TBI and no hazardous drinking reference category, than the other TBI and hazardous drinking classifications examined. Below we discuss each in turn.

Associations between TBI, problem drinking and current mental health issues

The results we report here replicate and extend previous results on the individual impact of hazardous drinking and TBI on mental health indicators.19 20 ORs among current hazardous drinkers were significantly higher for elevated psychological distress, being prescribed medication for anxiety, depression or both, being prescribed medication for ADHD, suicidal ideation, suicide attempt and self-rated fair or poor mental health in the past 12 months. Previous research has shown that depression, anxiety, ADHD or combinations of these conditions are risk factors for hazardous drinking among adolescents because some youth use drinking as a coping strategy for dealing with internal distress.39–41 Evidence also shows that adolescents diagnosed with mental disorders, including anxiety, depression and ADHD, have significantly elevated rates of alcohol problems.42 43

Adjusted ORs were significantly higher among adolescents who reported former TBI (but not recent TBI) for being prescribed medication for anxiety, depression or both, being prescribed medication for ADHD, suicidal ideation, suicide attempt, reporting fair or poor mental health and calling a crisis line for help compared to adolescents who never had a TBI and were not problem drinkers. These results replicate findings linking these mental health issues to long-term history of TBI.44 45 Recent TBI without hazardous drinking did not increase the odds of the mental health issues assessed here, with the exception of suicide attempts. Specifically, adolescents who reported recent TBI had nine times higher adjusted odds of reported attempted suicide in the past 12 months than those who never had a TBI and were not identified as hazardous drinkers. Suicide is the third leading cause of death among people aged 14–25 years and has recently been identified as a condition that is linked with TBI and hazardous drinking.25 46 47 A recent systematic review of studies published between 2007 and 2012 revealed that the link between suicidal ideation and TBI was robust,48 whereas a Canadian study of 235 000 adults found that adults with a history of concussions were three times more likely to die by suicide compared to individuals who never had a concussion.46 Our results confirm that each category of former TBI, recent TBI or hazardous drinking is strongly related to suicidal ideation and suicide attempt in adolescents. Most importantly, data here show that this link is intensified among adolescents experiencing both conditions. Specifically, compared to the rest of the TBI–hazardous drinking classifications we examined, the larger ORs for suicide attempts were observed among adolescents who were both hazardous drinkers and had recent TBI than among adolescents who never had a TBI, nor were problem drinkers. Therefore, it is important to be aware of the risk of suicide ideation and attempt associated with excessive alcohol use among youth who recently had a TBI, as well as the attitudes that these messages engender in adolescents with regard to self-inflicted harm. Overall, these results point to the urgent need for combined prevention efforts in school for TBI, alcohol use and suicide.

Hazardous drinkers with recent TBI had more and higher ORs for most current mental health behaviours than those with former TBI. To the best of our knowledge, this is the first time when temporarily interpretable patterns of association such as these have been demonstrated in a population-based study. However, given the correlational nature of our design, we cannot draw causal inferences. It is, therefore, unclear whether mental health issues, such as the ones examined here, represent immediate consequences of recent TBI that co-occur with problem drinking which, with the passage of time, may decrease in their ORs due to their identification and treatment (eg, prescribed medication and counselling), or risks for the TBI–problem drinking co-occurrence. Previous research evidence suggests that the increase in mental health issues in the first-year post-TBI with problem drinking is not uncommon. For example, depression is about eight times more common after TBI in the first-year postinjury when co-occurring with increased alcohol consumption, among adults.49 Alcohol post-TBI, short and long term, can interfere with prescribed medication leading to overdose, multiplying effects (alcohol plus other medication effects) or death.49 50 Furthermore, it is important to recognise that adolescents who consume alcohol are also more likely to use other substances and vice versa, particularly among TBI survivors.4 20 Given that many adolescents are involved not only with alcohol but also with other substances and may have a mental disorder and TBI, interventions should be designed to address these complexities. Taken together, these results demonstrate that considering whether the TBI occurred recently (past year) or previously (more than a year ago) may be an important consideration for clinicians, considering its contribution in the management of mental health conditions and rehabilitation efforts.

Associations between TBI, problem drinking and current conduct behaviours

Adolescents who were classified as hazardous drinkers with former TBI had more numerous and higher ORs for conduct behaviours than those with recent TBI. These results may suggest that the ORs of behavioural issues increase in the long term rather than subside, as one may expect. On the other hand, these results are not surprising if TBI is accompanied by other comorbid conditions (eg, hazardous drinking and mental health issues). On the other hand, some researchers found that conduct problems related to TBI often do not appear until several months or years following an injury unless the TBI is more severe.51 52 TBI sustained during youth can lead to sustained and persistent impaired functioning in many areas, including neurological, neuromuscular, neurocognitive and neuropsychiatric.51 The extent of these deficits is not fully understood or evident immediately after the injury. Postinjury problems with impulsivity, difficulty with paying attention and focused attention and restlessness post-TBI are common in about one-third of the youth.53 Older children and adolescents have more problems inhibiting behaviour that may be expressed through impatience, irritability, aggression and inappropriate comments,54 and may act on an impulse that could have been ignored before the injury. With the addition of alcohol use and other comorbidities, behavioural issues, violence and aggression are not uncommon.25 55

A social ecological perspective suggests that several social contexts and the interdependencies of these contexts contribute to the development of adolescent hazardous drinking, risk behaviours leading to TBI and alcohol misuse post-TBI.56–62 While adolescent problem drinking and TBI, especially sports injuries, have been recognised to be shaped by the socialisation contexts and processes,61 research on schools and neighbourhoods is far less common than that on family and peer influences.63 Yet, they both contribute and perpetuate the socialisation of co-occurring hazardous drinking and TBI.59 63 For example, aggressive play (seeking revenge on ice) in minor league hockey is often reinforced by the player's social environment and justified by players as a demonstration of loyalty to teammates and especially injured teammates.56 59 The social context is particularly relevant to the population examined here since the main mechanism of injury for recent TBIs among Ontario adolescents since 2011 has remained sports injuries, particularly team sports (eg, hockey and soccer).19 59 Overemphasis on winning in hockey games, group membership dynamics, coaches' motivation to further their own opportunities in the sport or parents' financial interest and vocational prospects for their child's future are a few of the factors that have been shown to contribute to the lack of management post-TBI in youth hockey by underreporting head injuries.59 While much of human behaviour is influenced by our genetic makeup, the socialisation process can mould it in particular directions by encouraging specific beliefs and attitudes as well as selectively providing experiences.58 61–63 The implication of the results we report here are important for prevention and monitoring in the long term, given the mental health and behavioural TBI aftermath consequences we observed. It may be useful for teachers, sports coaches and school guidance councillors to be made aware of students who have a history of TBI and to maintain ongoing communication with parents to prevent the development of harmful comorbid conditions over time.58 Prevention efforts may wish to consider forming a means of facilitating parents, sports coaches, clinicians and school guidance councillors to work together as a team to provide support for the adolescent in the short and long term who may be facing disruption of brain pathways dedicated to self-management, leading to conduct and behavioural issues. The results of our study warrant the need for a greater understanding of the ways in which sports and alcohol misuse socialisation combine to create, externally, a culture of violence and aggression, and, internally, mental health issues. Physicians, health professionals, researchers and concerned parents for their part can help in advocating interventions that involve all levels of social context and processes (eg, home, school and community); serve as role models for a healthy approach to sport and peer interactions and socialisation; counsel players, parents and coaches, and school guidance councillors; and raise awareness about safe play and the risks associated with certain practices in sports.

This is the first population-based study to compare the individual impact of current hazardous drinking and history of TBI with their combined effects on mental health and conduct behaviour outcomes. The results provide strong support for the suggestion that the negative effects of the co-occurrence of hazardous drinking with TBI may be synergistic. When hazardous drinking co-occurred with either former or recent TBI, the odds were significantly elevated for nearly all the mental health and perpetrator-related violent and non-violent conduct behaviours, as well as reports of being the victim of being threatened with a weapon on school property or being bullied at school or via the internet, compared to reporting only TBI or hazardous drinking. The incremental impact of the co-occurrence of hazardous drinking and TBI has not previously been demonstrated, but it appears substantial.

Limitations

At the same time, readers should be mindful of our study's limitations. First, the results are based on self-report and thus subject to bias that may affect validity. Second, the data are obtained from a cross-sectional survey and thus do not allow causal conclusions to be drawn. While our postsurvey assessment of substance use and mental health indicators did not show evidence of appreciable bias, the survey's student response rate (63%), while considered normative for such studies, may be subject to non-response bias.4 Although most clinical literature has investigated the relationship between TBI and mental health symptoms post-TBI, alcohol misuse and mental health problems may also be linked to risk-taking behaviours that precipitate TBI. Finally, our operational definition of TBI excluded milder forms of the injury that leaves the individual confused or dazed without loss of consciousness, or with a loss of consciousness for <5 min. Future studies should consider evaluating the role of date of first injury and level of TBI severity in the associations we reported here, which we did not assess.

Conclusion

Nevertheless, these results are of substantial interest. First, the results not only replicate but also extend findings that the joint occurrence of hazardous drinking and TBI among adolescents is associated with significant adverse mental health and conduct behaviour correlates. The incremental negative consequences of the co-occurrence of hazardous drinking and TBI in an adolescent population we report are novel. Additionally, whether the TBI occurred in the past year or previously may be an important consideration. Separation of recent from former TBI strengthens the ability to make causal interpretations. The TBI–AUDIT classifications are temporally interpretable (eg, past history of TBI vs current hazardous drinking assessment). This study contributes to the slowly developing international population studies assessing alcohol misuse and TBI.

Our results suggest that when dealing with adolescents with a drinking problem, it may be important to look for a history of TBI, and conversely, when dealing with adolescents with TBI, it may also be important to look for evidence of hazardous drinking, as co-occurrence appears to be associated with substantially greater mental health problems and conduct behaviours. Additional research to understand the incremental problems experienced by those with co-occurring hazardous drinking and TBI, and to understand the causal relationships involved, is greatly needed. Such examinations are crucial in helping guide clinicians, physicians, prevention and rehabilitation programmes.