Differences in the relationship of marijuana and tobacco by frequency of use: A qualitative study with adults aged 18-34 years.

Co-use of marijuana and tobacco is increasing among adults in the United States, but little research exists examining why co-use occurs. Changing marijuana policies make understanding the relationship between marijuana and tobacco critical. This study aimed to assess how adult co-users of marijuana and tobacco qualitatively conceptualize and describe their use and whether variation exists by frequency of use. Forty-eight past-month co-users aged 18-34 years completed semistructured, 1-on-1 qualitative interviews in Washington State (United States) in 2014. Interviews were digitally recorded, transcribed verbatim, coded, and analyzed overall and across frequency of use strata (high-tobacco/high-marijuana, high-tobacco/low-marijuana, low-tobacco/high-marijuana, and low-tobacco/low-marijuana). High-tobacco use was daily use; high-marijuana use was use on ≥20 of the past 30 days. The relationship between tobacco and marijuana varied by frequency of use and was strongest among high-tobacco use groups. Participants described the following patterns of and reasons for use: sequential use (e.g., using within short succession; due to addiction/habit, to enhance the high, or to counteract the effects of 1 substance), substitution (e.g., using in different times/places; due to liking the general act of smoking, limitations on when/where they could use a substance, or as a way to quit or cut down on 1 substance), or coadministration (e.g., simultaneous use; to adjust the dose of either tobacco or marijuana or to modulate the high/improve the flavor). Relationships between tobacco and marijuana varied based on frequency of use. These data can inform future surveillance and aid in the development of theoretical frameworks to explain why co-use occurs. (PsycINFO Database Record (c) 2016 APA, all rights reserved).