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

<h4>Background</h4>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.<h4>Methods</h4>Data were obtained from a longitudinal cohort study comprising 8598 Swedish men and women, aged 20-64, with a three-year-follow-up.<h4>Results</h4>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.<h4>Limitations</h4>Lack of information on frequency of cannabis use and of age of initiation of use.<h4>Conclusions</h4>We found no longitudinal associations between cannabis use and incidence of depression/anxiety, or between depression/anxiety and later cannabis use onset.