Cannabis use, depression and anxiety: A 3-year prospective population-based study

Whether or not cannabis use may increase the risk for depression and/or anxiety is not clear. For one thing, it has not been possible to draw a definitive conclusion regarding the direction of causality, i.e. whether cannabis use increases the risk for depression/anxiety or vice versa. This study aimed at examining possible associations between cannabis use, depression and anxiety, using all three measures as both exposure and outcome.

Data were obtained from a longitudinal cohort study comprising 8598 Swedish men and women, aged 20-64, with a three-year-follow-up.

Adjusted for sex and age, cannabis use at baseline was associated with an increased relative risk (RR) for depression and anxiety at follow-up, with RR=1.22 [1.06-1.42 Cl 95%] for depression and RR=1.38 [1.26-1.50 Cl 95%] for anxiety. Adjusted for all confounders (alcohol and illicit drug use, education, family tension, place of upbringing), the associations were no longer statistically significant; RR=0.99 [0.82-1.17 Cl 95%] for depression and RR=1.09 [0.98-1.20 Cl 95%] for anxiety. Age-adjusted, reporting depression or anxiety at baseline increased the risk of cannabis onset at follow-up three years later; RR=1.62 [1.28-2.03 CI 95%] and RR=1.63 [1.28-2.08 CI 95%] respectively. However, adjusted for other illicit drug use the associations were no longer statistically significant.

Lack of information on frequency of cannabis use and of age of initiation of use.

We found no longitudinal associations between cannabis use and incidence of depression/anxiety, or between depression/anxiety and later cannabis use onset.