INTRODUCTION: Marijuana (cannabis) use has become increasingly prevalent worldwide, raising concerns about its potential long-term health effects, particularly on the respiratory system. While tobacco smoking is a well-established risk factor for lung cancer,the association between cannabis use and lung cancer risk remains unclear and controversial. This systematic review and meta-analysis of existing observational studies aimed to evaluate the potential relationship between marijuana use and the risk ofdeveloping lung cancer.

METHODS: A systematic search was conducted across PubMed, Web of Science, and Scopus to identify cohort and case-controlstudies up to September 2025. Studies were selected, relevant data were extracted, and statistically analyzed using effect sizes (ES)and 95% confidence intervals (CI). All analyses were conducted using STATA software.

FINDINGS: This meta-analysis included six observational studies, comprising 16 effect sizes, consisting of two cohort studies andfour case-control studies. The pooled analysis of the cohort studies (7 effect sizes) indicated a statistically significant associationbetween marijuana (cannabis) smoking and increased lung cancer risk (ES: 2.06; 95% CI: [1.04-4.07]; =0.038; I=75%). Incontrast, the meta-analysis of the case-control studies (9 effect sizes) showed a non-significant increase in risk (ES: 1.16; 95% CI:[0.71-1.88]; =0.542; I=82%).

CONCLUSION: This meta-analysis indicates that marijuana smoking may increase lung cancer risk, with cohort studies showing asignificant twofold association. Although case-control studies were not statistically significant, the upward trend highlights theimportance of considering cannabis use in lung cancer risk assessments and patient counseling.