O1038 Oct.4: 5:16pm - Peer Influence on Teens' Usage of Marijuana and Tobacco Use and Urinary Biomarkers

Background
Adolescent dual use of marijuana and tobacco is well documented. In this secondary analysis of self-report survey data (n=517 adolescents, ages 12-21) and urinary biomarkers we sought to:
1. Describe influence of friends’ marijuana and tobacco use on both marijuana and tobacco usage.
2. Describe the relationship between friends’ marijuana and tobacco use on urinary biomarkers (THC, cotinine) for marijuana (THC) and tobacco users (cotinine).

Methods:
Bivariate and multivariable linear regression analyses were conducted using SPSS 26. Marijuana, e-cigarette, and cigarette users were categorized in 5 groups: daily users, weekly, monthly, ever and never users. Tobacco use included use of e-cigarettes or conventional cigarettes. The established cutoff (>=10ng/mL) indicating recent usage, was applied to urinary THC and cotinine levels for bivariate analyses. For multivariable analyses, continuous measures of THC and cotinine were used.

Results:
31.3% (162/517) of all respondents reported ever using marijuana; 53.7% reported past-month use; 36.5% past week use; 18.5% reported using in past 24 hours. Most common reasons for initial marijuana use were curiosity (72%) and friends’ use (40.7%). Other reasons included self-medicating for anxiety/depression.
Use of marijuana was associated with co-use of tobacco. Specifically, 79.4% of ever marijuana users also reported ever using tobacco (p<.001) and 91.7% of past-month marijuana users were also past-month tobacco users (p<.034). As described in the primary analysis which focused on e-cigarette users, urinary biomarkers correlated with self-report: 61.3% of those with THC >cutoff also had cotinine > cutoff (p<.001).
Friends’ use of marijuana was associated with own marijuana use: 71.2% of ever marijuana (p<.001) users and 82.4% of past-month marijuana users (p=.001) reported having friends who used marijuana around them. Urinary THC reflected the association with friends’ usage: 90.3% of those with THC > cutoff had friends who used marijuana (p<.001). Friends’ use of marijuana (Beta =163.58, p=.03) was an independent predictor of THC level in regression, when controlling for own marijuana use.
Friends’ use also showed a positive association with self-use of tobacco: 74.6% (p<.001) of ever tobacco users and 89.1% (p<.04) of past-month tobacco users reported having friends who used tobacco around them. Multivariable regression revealed that both self-use (Beta=84.58, p=.04) and friends’ use (Beta =88.29, p=.03) of tobacco were independent predictors of cotinine levels.

Conclusions:
Co-use of tobacco with marijuana was common and we found this to be corroborated by urinary biomarkers. Peer influence impacts adolescents’ usage of both marijuana and tobacco. The independent effects of friends’ usage on users’ urinary THC and cotinine levels support adolescent self-report. These findings have important implications for counseling adolescents about marijuana and tobacco usage, and underscore the significance of including the impact of peer influence in this discussion.