A meta-analysis of 14 cohort studies covering 17.5 million participants found cannabis users had 53% higher all-cause mortality than non-users, though the association was driven by general population studies and did not hold in patient populations.
Epidemiologists, public health researchers, cannabis policy analysts
53% higher mortality risk, but I²=98% heterogeneity
What the researchers found
Across 14 cohort studies with 17,545,076 participants (3,000,667 cannabis users), cannabis use was associated with a risk ratio of 1.53 (95% CI: 1.09-2.14) for all-cause mortality. The effect was significantly larger in prospective designs (RR 2.07) versus retrospective (RR 1.11), and in general population cohorts (RR 2.53) versus patient populations (RR 1.03). Larger sample sizes were associated with smaller effects. GRADE assessment rated overall evidence certainty as low.
Why it matters
This is the first meta-analysis to synthesize evidence on cannabis use and all-cause mortality. The finding of a 53% increased risk is notable but comes with substantial caveats: high heterogeneity, potential confounding, and the association disappearing in patient populations suggest the relationship is more complex than a simple causal link.
The numbers in context
n=17,545,076 (3,000,667 cannabis users); 14 cohort studies (50% prospective); overall RR 1.53 (95% CI: 1.09-2.14); general population RR 2.53; patient population RR 1.03; I²=98%; GRADE: low certainty
How the study worked
Systematic review and meta-analysis registered with PROSPERO (CRD42023396915). Searched Scopus, PubMed, Web of Science, and ProQuest through October 2023. Included cohort studies comparing cannabis users to non-users for all-cause mortality. Random-effects meta-analysis with sensitivity analysis, meta-regression, and Newcastle Ottawa Scale quality assessment.
What this study cannot tell us
Very high heterogeneity (I²=98%) reduces confidence in the pooled estimate. Unadjusted estimates included in many studies mean confounding factors (tobacco, alcohol, socioeconomic status) likely inflate the association. GRADE assessment rated evidence as low certainty. Larger studies showed smaller effects, suggesting potential publication bias or confounding.
How to read the evidence
Meta-analysis of cohort studies provides important synthesis, but very high heterogeneity, unadjusted estimates, and GRADE-rated low certainty significantly limit confidence in the pooled estimate.
When this study was published
2025 publication; searched through October 2023; PROSPERO registered
The bigger picture
Whether cannabis use itself increases mortality or whether cannabis users have other risk factors that drive mortality remains one of the most consequential unanswered questions in cannabis epidemiology. This meta-analysis finds an association but cannot resolve the causation question due to the limitations of the underlying studies.
Questions still open
- Would fully adjusted analyses controlling for tobacco, alcohol, and socioeconomic factors change the mortality association? Why was the association absent in patient populations but present in general population cohorts?
Common questions
Does cannabis use increase the risk of death?
Why was heterogeneity so high?
Read the original research
Relative Risk of All-Cause Mortality Associated With Cannabis Use: A Systematic Review and Meta-Analysis of Cohort Studies.
Health science reports, 8(10), e71212
Citation
Alimoradi, Zainab; Lin, Chung-Ying; Myran, Daniel T; Solmi, Marco; Pakpour, Amir H. (2025). Relative Risk of All-Cause Mortality Associated With Cannabis Use: A Systematic Review and Meta-Analysis of Cohort Studies.. Health science reports, 8(10), e71212. https://doi.org/10.1002/hsr2.71212