Polysubstance use and mental health among young adults.

Objectives: To describe mental health indicators according to regular (i.e., weekly or daily) alcohol, cannabis, and/or nicotine use in a population-based sample of young adults.

Methods: Data for 733 participants (mean age = 30.6 years) were drawn from cycle 23 of the ongoing Nicotine Dependence In Teens study, Montreal, Canada. The associations between (i) number of substances used and (ii) pattern of polysubstance use and each of depressive symptoms, anxiety symptoms, and positive mental health (PMH) were modeled using multivariable linear regression adjusting for age, sex, and education.

Results: Median (IQR) scores for depressive symptoms (range 0-50), anxiety symptoms (range 0-21), and PMH (range 0-70) were 8.0 (7.0), 4.0 (6.0), and 43.0 (18.0), respectively. One third (37%) of participants did not report regular use of any substance; 42%, 16%, and 5% reported regular use of one, two, or three substances, respectively. There was no dose-response association between number of substances used and any mental health indicator. Relative to no substance use, regular use of two substances was associated with more frequent anxiety symptoms ( $\hat{\beta }$  [95% CI] = 1.32 [0.34, 2.31]) and lower PMH (-3.64 [-6.34, -0.95]). Specifically, the cannabis-nicotine combination was associated with more frequent anxiety symptoms (2.58 [1.06, 4.10]) and lower PMH (-5.90 [-10.04, -1.76]). The alcohol-nicotine combination was associated with lower PMH (-3.70 [-7.30, -0.10]).

Conclusion: Specific pairings of alcohol, nicotine, and cannabis may be important in their associations with mental health. Longitudinal studies in population-based samples of young adults are needed to replicate these findings before their implications for public health programming can be considered.