Regular Cannabis Use Lowers Remission Rates in Bipolar Disorder | Research

The takeaway

In a 24-month study, regular cannabis use was associated with significantly lower remission rates in patients with bipolar I and schizoaffective disorder, with the worst outcomes in those who also smoked tobacco.

Read this if you or someone you know has bipolar disorder and uses cannabis regularly.

Combined cannabis and tobacco users had the lowest remission rates

What the researchers found

Researchers followed 234 patients with bipolar I disorder or schizoaffective disorder for 24 months. About 11% were regular cannabis users (three or more times per week).

Cannabis use was significantly associated with lower likelihood of achieving remission. The pattern differed by sex: in women, cannabis was linked to lower depression remission, while in men, it was linked to lower mania remission.

The lowest remission rates were in patients who used both cannabis and tobacco, followed by tobacco-only users, with non-smokers having the best outcomes.

Why it matters

This study provides longitudinal evidence that cannabis use complicates bipolar disorder treatment, and reveals that the impact may differ between men and women and interact with tobacco use.

The numbers in context

234 participants analyzed; 25 (10.7%) regular cannabis users; 24-month follow-up; combined cannabis and tobacco group had the lowest remission rates; sex-specific effects on depression (women) versus mania (men)

How the study worked

Prospective observational study following 239 patients with bipolar I or schizoaffective disorder (bipolar type) over 24 months. Regular cannabis use defined as three or more times per week. Outcomes measured using the Hamilton Depression Rating Scale and Young Mania Rating Scale at evaluations throughout the follow-up period.

What this study cannot tell us

Observational design cannot prove cannabis caused worse outcomes. Regular cannabis users may differ from non-users in ways not fully captured. Small number of cannabis users (n=25) limits statistical power. Dose and potency were not measured.

How to read the evidence

Prospective 24-month follow-up with validated outcome measures, though limited by small cannabis user subgroup and observational design.

When this study was published

Published in 2015. Treatment approaches for bipolar disorder have continued to evolve.

The bigger picture

For people with bipolar spectrum disorders, cannabis use appears to work against the goals of treatment. The interaction with tobacco and sex-specific effects suggest that substance use management needs to be individualized within bipolar treatment plans.

Questions still open

Why does cannabis appear to affect depression in women but mania in men with bipolar disorder? Would reducing cannabis use improve remission rates? Does the type or potency of cannabis matter?

Common questions

Why did cannabis affect men and women differently?

In women, cannabis was linked to lower depression remission, while in men it was linked to lower mania remission. The biological mechanisms are unclear, but sex differences in cannabinoid receptor density and hormonal interactions may play a role.

Does this mean cannabis causes bipolar episodes?

The study found an association between cannabis use and lower remission rates but cannot prove causation. It is possible that people with more severe illness are also more likely to use cannabis.

Read the original research

Impact of Cannabis Use on Long-Term Remission in Bipolar I and Schizoaffective Disorder.

Psychiatry investigation, 12(3), 349-55

View on PubMed ↗Publisher’s paper ↗

Citation

Kim, Sung-Wan; Dodd, Seetal; Berk, Lesley; Kulkarni, Jayashri; de Castella, Anthony; Fitzgerald, Paul B; Kim, Jae-Min; Yoon, Jin-Sang; Berk, Michael. (2015). Impact of Cannabis Use on Long-Term Remission in Bipolar I and Schizoaffective Disorder.. Psychiatry investigation, 12(3), 349-55. https://doi.org/10.4306/pi.2015.12.3.349