Marijuana Use and the Risk of Depression: A Systematic Review and Meta‐Analysis

Abstract

Objective: To conduct a systematic review of the evidence pertinent to the relationship between marijuana use and depression and perform a meta‐analysis on the data in order to inform evidenced‐based practice. The question of interest is: Is marijuana use associated with increased risk of developing depression? Methods: The databases MEDLINE (PubMed), The Cochrane Library, CINAHL (EBSCO), psycINFO, and Google Scholar were searched for the topics of marijuana use and depression through October of 2013. Studies were included if they were systematic reviews, randomized controlled trials, prospective or retrospective cohort studies, or case‐control studies. No randomized controlled trials were discovered. Quality of cohort and case‐control studies was evaluated using the Newcastle‐Ottawa Quality Assessment Scale 1. Overall quality of evidence was determined using the GRADE methodology 2,3. The Bradford‐Hill criteria 4 were used to assess for causation. Studies were assessed by two reviewers. 173 articles were screened for eligibility. Of these fourteen articles were considered to fit the inclusion criteria. Nine homogeneous studies were included in the meta‐analysis. Results: The quality of the evidence reviewed is low to very low. It does not meet Bradford‐Hill criteria for causation. There is a slight positive correlation between marijuana use and onset of depression. However, those studies included in the meta‐analysis demonstrated a low overall pooled odds ratio (OR = 1.17; 95% CI = 1.06—1.29). Conclusion: The evidence suggests a slight positive correlation between marijuana use and depression but is not sufficient to draw a conclusion. This evidence is generally of very low quality. It does not demonstrate a dose response, and is without a significant magnitude of effect.