Among 733 young adults in Montreal, the cannabis-nicotine combination was associated with the highest anxiety and lowest positive mental health, while no dose-response existed for number of substances.
Substance use researchers, young adult health providers, harm reduction specialists
Cannabis-nicotine was the worst combination for anxiety and wellbeing
What the researchers found
No dose-response between substance count and mental health; cannabis-nicotine had strongest negative associations (anxiety b=2.58, PMH b=-5.90); alcohol-nicotine also linked to lower positive mental health.
Why it matters
Specific substance pairings matter more for mental health than total count, with cannabis-nicotine standing out as particularly problematic.
The numbers in context
733 participants; 37% no regular use, 42% one, 16% two, 5% three; cannabis-nicotine: anxiety b=2.58 (1.06-4.10), PMH b=-5.90 (-10.04 to -1.76).
How the study worked
Cross-sectional analysis of 733 NDIT study participants (mean age 30.6); multivariable linear regression for regular alcohol, cannabis, and nicotine use patterns.
What this study cannot tell us
Cross-sectional; self-reported; single Canadian city; small subgroup sizes; reverse causation possible.
How to read the evidence
Population-based cohort with specific combination analysis, but cross-sectional design limits causal interpretation.
When this study was published
Published 2025
The bigger picture
Public health messaging should highlight specific combinations rather than simply counting substances.
Questions still open
- Why is cannabis-nicotine particularly harmful? Is it pharmacological interaction or shared risk factors? Would cessation of one substance improve outcomes?
Common questions
Does using more substances mean worse mental health?
Which combination was most harmful?
Read the original research
Polysubstance use and mental health among young adults.
Canadian journal of public health = Revue canadienne de sante publique, 116(6), 849-857
Citation
Chopra, Rajit; Sylvestre, Marie-Pierre; Pelekanakis, Annie; Doré, Isabelle; Omorou, Abdou Y; O'Loughlin, Jennifer. (2025). Polysubstance use and mental health among young adults.. Canadian journal of public health = Revue canadienne de sante publique, 116(6), 849-857. https://doi.org/10.17269/s41997-025-01035-3
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