Cannabis Use Nearly Tripled the Risk of Developing Manic Symptoms Over Three Years | Research

The takeaway

In a population-based study of 4,815 adults followed for three years, cannabis use at baseline increased the risk of developing manic symptoms by 2.7-fold, independent of psychotic symptoms, and there was no evidence that mania led to cannabis use.

Read this if you want to understand the research linking cannabis use to bipolar symptoms, particularly mania.

Cannabis use increased mania risk 2.7-fold, with no evidence that mania led to cannabis use

What the researchers found

Researchers followed 4,815 individuals aged 18-64 years in a longitudinal population-based study with assessments at baseline, one year, and three years. Cannabis use at baseline increased the risk of developing manic symptoms during follow-up (adjusted odds ratio 2.70, 95% CI: 1.54-4.75).

This association held after adjusting for age, sex, education, ethnicity, marital status, neuroticism, use of other drugs, alcohol use, depressive symptoms, and manic symptoms at baseline. Importantly, the cannabis-mania association was independent of psychotic symptoms, meaning it was not simply a manifestation of cannabis-related psychosis.

There was no evidence for reverse causality: manic symptoms at baseline did not predict the onset of cannabis use during follow-up (OR = 0.35, 95% CI: 0.03-3.49), arguing against the self-medication explanation.

Why it matters

While the cannabis-psychosis link is well-studied, much less was known about cannabis and mania/bipolar disorder. This study provided some of the strongest prospective evidence that cannabis use increases the risk of manic symptoms specifically, independent of psychosis, and that this is not explained by self-medication.

The numbers in context

4,815 adults followed for 3 years. Cannabis use increased mania risk: adjusted OR 2.70 (95% CI: 1.54-4.75). Association independent of psychotic symptoms. No reverse causality: baseline mania did not predict future cannabis use (OR = 0.35).

How the study worked

Longitudinal population-based cohort study. 4,815 individuals aged 18-64 assessed with the Composite International Diagnostic Interview at baseline, 1-year, and 3-year follow-up. Assessed substance use, manic symptoms, psychotic symptoms, and potential confounders. Adjusted odds ratios calculated for prospective associations.

What this study cannot tell us

Three years is relatively short for detecting long-term effects on bipolar disorder risk. Self-reported cannabis use may be underestimated. The Composite International Diagnostic Interview assesses symptoms rather than clinical diagnoses. The study population was from the Netherlands, which may not generalize to all populations.

How to read the evidence

Large population-based prospective cohort study with comprehensive adjustment for confounders and reverse causality analysis. Strong study design for this type of question.

When this study was published

Published in 2006. Subsequent research has generally supported the association between cannabis use and increased risk of manic symptoms.

The bigger picture

Cannabis is commonly used by people with bipolar disorder, but the direction of causation has been unclear. This study's prospective design and lack of reverse causality provide evidence that cannabis may contribute to manic symptoms rather than simply being used as self-medication by people already experiencing them.

Questions still open

Does the increased risk of manic symptoms translate to increased rates of bipolar disorder diagnosis over longer follow-up? Does the type or potency of cannabis affect the mania risk?

Common questions

Can cannabis cause bipolar disorder?

This study found cannabis use nearly tripled the risk of developing manic symptoms over three years, and ruled out reverse causality (people with mania using cannabis to self-medicate). However, it measured manic symptoms rather than bipolar disorder diagnoses, and three years may be too short for definitive conclusions about disorder development.

Is the cannabis-mania link just part of the cannabis-psychosis link?

No. The association between cannabis and manic symptoms was independent of psychotic symptoms. This means the increased mania risk was not simply due to cannabis causing psychotic experiences that happened to include manic features.

Read the original research

Cannabis use and expression of mania in the general population.

Journal of affective disorders, 95(1-3), 103-10

View on PubMed ↗

Citation

Henquet, Cécile; Krabbendam, Lydia; de Graaf, Ron; ten Have, Margreet; van Os, Jim. (2006). Cannabis use and expression of mania in the general population.. Journal of affective disorders, 95(1-3), 103-10.