1 Department of Psychology, York University, Toronto, Ontario, Canada.
2 Institute for Mental Health Policy Research, Centre for Addiction and Mental Health, Toronto, Ontario, Canada.
3 Department of Psychiatry, University of Toronto, Toronto, Ontario, Canada.
4 Department of Addictions, Kings College London, London, UK.
5 Department of Psychology, Concordia University, Montreal, Quebec, Canada.
6 Department of Population and Public Health Sciences, University of Southern California, Los Angeles, California, USA.
7 Institute for Addiction Science, University of Southern California, Los Angeles, California, USA.

Background: This study examined motivational pathways between internalizing symptoms (i.e., depression, anxiety, stress) and simultaneous alcohol and cannabis use among young adults.

Methods: Participants (N = 151; 64% female, Mean age = 22.07) completed baseline questionnaires assessing internalizing symptoms and simultaneous use motives, and then reported their alcohol and cannabis use each day for 21 days. Participants repeated these procedures again 6 months and 12 months postbaseline. Daily survey responses were used to calculate the number of simultaneous use days involving heavy drinking (4 or more drinks for females; 5 or more drinks for males) and light drinking at each wave for each participant. The total number of negative consequences reported across all simultaneous use days was also calculated for each participant at each wave.

Results: Multilevel mediation analyses revealed that within-person increases in internalizing symptoms (a latent factor consisting of depression, anxiety, and stress indicators) at a given wave were indirectly associated with (a) a greater number of heavy drinking simultaneous use days (controlling for number of cannabis-only days and heavy drinking alcohol-only days) and (b) greater negative consequences on simultaneous use days (controlling for negative consequences on cannabis-only and alcohol-only days). These within-person associations were mediated by increases in positive (i.e., reward/enhancement) motives for simultaneous use. At the between-person level, greater average internalizing symptoms (aggregated across waves) were indirectly associated with more light drinking simultaneous use days via coping motives, and with fewer heavy drinking simultaneous use days via conformity motives (controlling for frequency of single substance use).

Conclusions: Young adults may combine cannabis with heavy episodic drinking more frequently during periods when they experience elevations in internalizing symptoms, mediated by a desire to achieve the positive/enhancing effects of simultaneous use. Findings may inform alcohol and cannabis harm reduction interventions tailored for young adults with internalizing symptoms.