Marijuana (Cannabis) Smoking Increases the Risk of Lung Cancer: Evidence from a Systematic Review and Meta-Analysis.

Karimi M.; Kazemi K.; Pourhanifeh M.; Irajian P.; Asbaghi O. · Addiction & health · 2026

**Background & Methods** This systematic review and meta-analysis evaluated the association between marijuana smoking and lung cancer risk by searching PubMed, Web of Science, and Scopus through September 2025. Six observational studies (2 cohort and 4 case-control studies) comprising 16 effect sizes were analyzed using STATA software to calculate pooled effect sizes with 95% confidence intervals. **Key Findings** • Cohort studies (7 effect sizes) demonstrated a statistically significant twofold increased risk of lung cancer associated with cannabis smoking (ES: 2.06; 95% CI: [1.04-4.07]; P=0.038), with substantial heterogeneity (I²=75%) • Case-control studies (9 effect sizes) showed a non-significant upward trend in lung cancer risk (ES: 1.16; 95% CI: [0.71-1.88]; P=0.542), with high heterogeneity (I²=82%) • The divergent findings between study designs suggest cannabis smoking may increase lung cancer risk, warranting consideration in clinical risk assessments and patient counseling **Dosage & Administration** Not reported. The studies evaluated cannabis smoking exposure without specifying standardized dosage, frequency, or duration metrics. **Safety & Adverse Effects** Not reported in detail. The meta-analysis focused specifically on lung cancer as an outcome; other respiratory or systemic adverse effects of cannabis smoking were not discussed. **Evidence Quality** This meta-analysis has several limitations. The inclusion of only six observational studies with small sample sizes limits generalizability. Significant heterogeneity (I²=75-82%) in both analyses suggests substantial variability in study designs, populations, and exposure assessments. The discordance between cohort and case-control findings raises concerns about study design-related bias; case-control studies are more vulnerable to recall and selection bias. Confounding variables (tobacco co-use, occupational exposures, socioeconomic factors) were not systematically assessed across studies. The evidence is classified as moderate quality observational data. Publication bias was not formally assessed. Future high-quality prospective cohort studies with standardized cannabis exposure metrics, comprehensive confounder adjustment, and adequate follow-up duration are needed to establish causality and quantify absolute risk.

More recent cannabis research