Cannabis Use Associated with Later Manic Symptoms and Bipolar Disorder

Cannabis use was associated with an increased risk of subsequent bipolar disorder (BD) and manic or hypomanic symptoms, according to a systematic review and meta-analysis published online as a journal pre-proof in the Journal of Affective Disorders.

The authors noted that BD affects approximately 2% of the population and that identifying modifiable risk factors before illness onset is a research priority. Although cannabis use is common, its role in the onset of bipolar-spectrum outcomes remains unclear, and earlier reviews were limited by few included studies or pooling of distinct outcomes, the investigators wrote.

The registered review searched PubMed and Web of Science from inception to October 2025 for longitudinal observational studies comparing cannabis-exposed and unexposed individuals without prior BD. Nineteen studies were included, totaling 6,960,517 participants (mean age, 23.8 years; 49% female), of whom 67,992 were cannabis users. Using random-effects meta-analyses, the investigators calculated unadjusted risk ratios (RRs). Cannabis use was associated with an increased risk of incident BD (RR, 2.46; 95% CI, 1.57-3.84; 8 studies) and manic or hypomanic symptoms (RR, 2.11; 95% CI, 1.07-4.18; 6 studies).

According to the investigators, the risk was robust across cannabis use definitions and age groups, although moderator analyses identified significant clinical and methodological sources of heterogeneity. Newcastle–Ottawa Scale scores ranged from 6 to 9, indicating good to high methodological quality.

The pooled estimates were unadjusted, and the authors noted that the findings cannot be interpreted as proof of direct causality. They suggested that cannabis use may represent a modifiable risk factor for bipolar-spectrum disorders and that routine evaluation of cannabis use, alongside prevention strategies to delay initiation and reduce use, may be warranted.

Source: Sanjuan-Ortiz C, Querol P, Aymerich C, et al. Cannabis use and subsequent onset of manic symptoms and bipolar disorder: a systematic review and meta-analysis. J Affect Disord. Published online October 6, 2026. doi:10.1016/j.jad.2026.122588