In a large HIV cohort tracked from 2009–2023, increasing cannabis use frequency was not associated with decreasing alcohol or tobacco use, and decreasing cannabis was not associated with increasing other substance use — challenging the substitution hypothesis for this population.
HIV care providers, addiction medicine specialists, and harm reduction advocates evaluating cannabis substitution claims.
What the researchers found
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.
Why it matters
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.
The numbers in context
CNICS HIV cohort, 2009–2023. Two trajectories analyzed: increasing cannabis use (initiation + increased frequency) and decreasing cannabis use (abstinence + reduced frequency). Neither direction of change predicted opposite changes in alcohol or tobacco use.
How the study worked
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.
What this study cannot tell us
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.
How to read the evidence
Large longitudinal cohort with sophisticated time-updated models, providing good evidence against substitution in this specific population.
When this study was published
Published 2025, data from 2009–2023.
The bigger picture
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.
Questions still open
- Does the substitution effect depend on the specific reason for cannabis use (medical vs. recreational)? Would structured medical cannabis programs with explicit substitution goals produce different results? Is the substitution hypothesis valid in any population?
Common questions
Doesn't cannabis help people drink less?
Why does this matter for people with HIV?
Read the original research
Brief report: Are changes in cannabis use frequency associated with changes in alcohol use and smoking among people with HIV (PWH) - A substitution question.
Drug and alcohol dependence, 277, 112958
Citation
Whitney, Bridget M; Delaney, Joseph A C; Drumright, Lydia N; Nance, Robin M; Fredericksen, Rob J; Chander, Geetanjali; Cachay, Edward R; Fox, Nathaniel T; Christopoulos, Katerina A; Cropsey, Karen L; Owens, Michael A; Burkholder, Greer A; Mayer, Kenneth H; McCaul, Mary E; Napravnik, Sonia; O'Cleirigh, Conall; Webel, Allison R; Yendewa, George A; Saag, Michael S; Kitahata, Mari M; Crane, Heidi M; Hahn, Andrew W. (2025). Brief report: Are changes in cannabis use frequency associated with changes in alcohol use and smoking among people with HIV (PWH) - A substitution question.. Drug and alcohol dependence, 277, 112958. https://doi.org/10.1016/j.drugalcdep.2025.112958
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