Association between Friends' Use of Nicotine and Cannabis and Intake of both Substances among Adolescents.

Nicotine and cannabis use are common among adolescents and may be associated with behavioral problems, poor academic outcomes and use disorders. The goals of this analysis were the following: (1) Describe the influence of friends' nicotine and cannabis smoking and vaping on self-reported use. (2) Describe the relationship between friends' nicotine and cannabis use on participants' urinary biomarkers of nicotine (cotinine) and cannabis (11-nor-9-carboxy-Δ⁸tetrahydrocannabinol=THC-COOH). This is a secondary analysis of survey and biomarker data collected in adolescents aged 12-21 between April 2017 and April 2018, in Long Island, New York. Bivariate and multivariable analyses were conducted using SPSS 26. A cutoff value of ≥10 ng/mL was used to signify recent usage for urinary cotinine and THC-COOH levels. Over one-third of the 517 surveyed adolescents reported using tobacco and one-third reported using cannabis. A significant relationship between friends' substance use and self-use was found. For both tobacco and cannabis, over 90% ( < 0.01) of participants with urinary biomarker levels above cutoff had friends who used the respective substance. Friends' nicotine and friends' cannabis use were each independently associated with urinary biomarker levels for those substances (for nicotine, beta = 88.29, = 0.03; for cannabis, beta = 163.58, = 0.03). Friends' use of nicotine and cannabis is associated with adolescents' intake, as well as the physiological exposure to those substances. These findings underscore the importance of including peer influence in the discussion with adolescents about tobacco and cannabis use.