Cannabis Use Made Bipolar Disorder Treatment Outcomes Worse Over 12 Months | Research

The takeaway

Among 3,459 bipolar disorder patients followed for 12 months, cannabis users showed less treatment compliance and higher levels of illness severity, mania, and psychosis compared to non-users.

Read this if you have bipolar disorder and use cannabis or are considering it.

3,459 bipolar patients: cannabis users had more mania, psychosis, and less treatment compliance

What the researchers found

In an observational study of 3,459 bipolar disorder patients (both inpatient and outpatient), researchers tracked the influence of cannabis use on treatment outcomes over one year.

Cannabis users exhibited less medication compliance and higher levels of overall illness severity, mania, and psychosis compared to non-users throughout the 12-month treatment period.

Cannabis users also experienced less life satisfaction and had a lower probability of being in a relationship.

There was little evidence that these associations were explained by third variables (mediators), suggesting an independent impact of cannabis on clinical outcomes in bipolar disorder.

The impact on psychopathological outcomes was pronounced, while the impact on social outcomes was more modest.

Why it matters

With a large sample and mediation analysis finding little evidence of confounding, this study provided relatively strong evidence that cannabis independently worsens bipolar disorder outcomes.

The numbers in context

3,459 bipolar patients followed for 12 months. Cannabis users had higher overall illness severity, mania, psychosis, lower treatment compliance, less life satisfaction, and lower relationship probability.

How the study worked

Observational longitudinal study (EMBLEM) enrolling 3,459 bipolar in- and outpatients. Cannabis exposure was assessed and clinical/social outcomes were tracked over 12 months. Mediation analysis tested whether third variables explained the cannabis-outcome associations.

What this study cannot tell us

Observational design cannot definitively establish causation. Cannabis users may have more severe illness at baseline. Self-reported cannabis use may be unreliable. The study did not quantify cannabis use amounts.

How to read the evidence

Large longitudinal observational study with mediation analysis. Strong sample size but observational design limits causal inference.

When this study was published

Published in 2009. Subsequent research has generally supported the finding that cannabis use complicates mood disorder treatment.

The bigger picture

While much research has focused on cannabis and schizophrenia, this study showed that cannabis also affects outcomes in bipolar disorder, broadening the evidence that cannabis use complicates the treatment of serious mental illness.

Questions still open

Does cannabis use cause worse bipolar outcomes or do more severe patients use cannabis? Would cannabis cessation improve bipolar treatment response? Are certain bipolar subtypes more affected by cannabis use?

Common questions

Does cannabis make bipolar disorder worse?

This large study found that cannabis-using bipolar patients had worse outcomes across multiple measures. While observational data cannot prove causation, the mediation analysis found little evidence that other factors explained the association.

Could cannabis help with some bipolar symptoms?

Some bipolar patients report using cannabis for symptom management. However, this study found that cannabis users had worse overall outcomes including more mania and psychosis, suggesting that any perceived benefits may not outweigh the harms at a population level.

Read the original research

Does cannabis use affect treatment outcome in bipolar disorder? A longitudinal analysis.

The Journal of nervous and mental disease, 197(1), 35-40

View on PubMed ↗Publisher’s paper ↗

Citation

van Rossum, Inge; Boomsma, Maarten; Tenback, Diederik; Reed, Catherine; van Os, Jim. (2009). Does cannabis use affect treatment outcome in bipolar disorder? A longitudinal analysis.. The Journal of nervous and mental disease, 197(1), 35-40. https://doi.org/10.1097/NMD.0b013e31819292a6