Frequent Cannabis Use Linked to Depression, Suicidal Thoughts

Early and heavy cannabis use is associated with an increased risk of major depressive disorder (MDD) and suicidal thoughts and behaviors, according to a recent study.

For their logistic regression analysis, researchers used retrospective data from 13,986 same-sex monozygotic and dizygotic twin pairs from the Australian Twin Registry 1992-1993, 1996-2000, and 2005-2009 (samples 1, 2, and 3, respectively). Significant associations were further adjusted for covariates, including alcohol or nicotine use, dysphoric and anhedonic mood, conduct disorder, and childhood abuse.
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Overall, cannabis use ranged from 30.4% in sample 1 to 69% in sample 3, and mean age of first cannabis use ranged from 17.9 years in sample 3 to 21.1 years in sample 1. Frequent use was reported by 15.9% of sample 1 and 21.9% of sample 3. Suicidal ideation was reported in 24.9% of sample 1, 26.3% of sample 2 and 26.2% of sample 3. MDD was present in 20.3% of sample 1 and 28.3% of sample 2. Monozygotic twins who used cannabis frequently were more likely to report MDD and suicidal ideation than their identical twin who used cannabis less frequently.

“The increased likelihood of MDD and suicidal ideation in frequent cannabis users cannot be solely attributed to common predisposing factors,” the researchers reported.

—Michael Potts

Reference:

Agrawal A, Nelson EC, Bucholz KK, et al. Major depressive disorder, suicidal thoughts and behaviours, and cannabis involvement in discordant twins: a retrospective cohort study [published online July 24, 2017]. Lancet Psychiatry. doi: http://dx.doi.org/10.1016/S2215-0366(17)30280-8.