People With HIV Who Increased Cannabis Use Did Not Decrease Their Alcohol or Tobacco Use

Among people with HIV, increasing cannabis use (initiation or increased frequency) was not associated with subsequent decreases in alcohol or tobacco use. Similarly, decreasing cannabis use was not associated with subsequent increases in alcohol or tobacco use. The harm reduction-based substitution hypothesis was not supported in this population.

Longitudinal analysis from the CNICS cohort (Centers for AIDS Research Network of Integrated Clinical Systems) between 2009 and 2023. Time-updated multivariable linear mixed models and joint longitudinal trajectory analysis examined associations between changes in cannabis use frequency and subsequent alcohol and tobacco use.

The cannabis substitution hypothesis — that increasing cannabis use reduces more harmful alcohol or tobacco use — is often used to justify cannabis use, especially for medical purposes. This study finds no evidence for this effect in people living with HIV, an important population where substance use affects treatment outcomes.

Substitution claims are central to many medical cannabis arguments. This evidence from a well-characterized HIV cohort suggests that adding cannabis doesn't automatically reduce other substance use — and may simply add to the overall substance burden these patients carry.

HIV-specific cohort — findings may not generalize to general population. Self-reported substance use. Cannot capture nuances of use (e.g., heavy vs. moderate). Observational — unmeasured confounders possible. CNICS participants may differ from all people with HIV.