Cannabis use in early adulthood and later prescription of antipsychotics, mood stabilisers, antidepressants and anxiolytics.

Background: The association between cannabis and psychosis and bipolar disorder has substantial support, while the evidence is more mixed for cannabis and depression and anxiety. Few studies have compared all these mental health outcomes in relation to cannabis use in a longitudinal design. Prescribed medicines commonly used to treat a mental disorder can be viewed as a proxy for the disorder. This longitudinal study investigates later prescription of several types of psychoactive drugs one to nine years after self-reported use of cannabis.

Methods: Data on cannabis exposure and relevant confounders were obtained from the longitudinal Young in Norway Study, providing survey data from four data collection waves between 1992 and 2006. Data were coupled with information about prescription of psychoactive drugs from the Norwegian Prescription Register between 2007 and 2015. The present study included 2,602 individuals. Descriptive analyses and logistic regression analyses were conducted.

Results: Past year use of cannabis increased the risk of antipsychotics prescription by almost six times (OR = 5.92; 95 % CI 2.29-13.16), and also increased the risk of prescription of mood stabilizers (OR = 4.66; 2.15 – 10.09) and antidepressants (OR = 2.10; 1.45 – 3.04). The associations remained after adjustment for sociodemographic variables, mental distress, conduct problems and use of other drugs.

Limitations: The psychoactive medicines may have been given for some other condition than a mental disorder, and it would have been preferable with a more fine-graded differentiation of cannabis exposure.

Conclusions: In this longitudinal study of young adults from the general population, past year cannabis use increased the risk for later prescriptions for antipsychotics, mood stabilizers and antidepressants.