Cannabis use may increase risk of bipolar and unipolar depression

A new study published in the Journal of American Medical Association suggests that bipolar illness, both psychotic and nonpsychotic, and unipolar depression have been linked to cannabis use disorder (CUD).

Cannabis usage is on the rise everywhere and is thought to be linked to a higher risk of developing mental illnesses; however, the link with affective disorders has not been properly researched. In order to determine whether cannabis use disorder is linked to a higher risk of both psychotic and nonpsychotic unipolar depression and bipolar disorder, as well as to compare these associations, Oskar Hougaard Jefsen and colleagues conducted this study.

All people who were alive, at least 16 years old, and residing in Denmark between January 1, 1995, and December 31, 2021 were included in this prospective, population-based cohort research utilizing Danish countrywide records. Bipolar disorder or unipolar depression with psychotic or nonpsychotic features was the primary result. Using Cox proportional hazards regression with time-varying information on CUD, adjusting for sex, substance use disorder, alcohol use disorder, being born in Denmark, parental educational level (highest attained), calendar year, alcohol, parental cannabis, or substance use disorders, and parental affective disorders, associations between CUD and subsequent affective disorders were estimated as hazard ratios (HRs).

The key findings of this study were:

1. A total of 119 526 786 person-years were spent following up with 6 651 765 people (50.3% of whom were female).

2. Unipolar depression, psychotic unipolar depression, and nonpsychotic unipolar depression were all related with an elevated likelihood of cannabis use disorder.

3. Cannabis usage was linked to a higher incidence of nonpsychotic, psychotic, and nonpsychotic psychotic bipolar disorder in both men and women.

4. However, not unipolar depression, cannabis use disorder was linked to a greater risk for psychotic than nonpsychotic bipolar disorder subtypes.

Reference:

Jefsen, O. H., Erlangsen, A., Nordentoft, M., & Hjorthøj, C. (2023). Cannabis Use Disorder and Subsequent Risk of Psychotic and Nonpsychotic Unipolar Depression and Bipolar Disorder. In JAMA Psychiatry. American Medical Association (AMA). https://doi.org/10.1001/jamapsychiatry.2023.1256