Cannabis use and risk of psychosis: an etiological link?

OBJECTIVE: The nature of the link between cannabis use and psychosis remains to be clarified.

METHOD: The paper reviews the evidence suggesting that cannabis may be a risk factor for psychosis onset.

RESULTS: Cross-sectional and retrospective epidemiological studies show that individuals with psychosis use cannabis more often than other individuals in the general population. It has long been considered that this association is explained by the self-medication hypothesis, postulating that cannabis is used to self-medicate psychotic symptoms. This hypothesis has been recently challenged by several prospective studies carried out in population-based samples, showing that cannabis exposure is associated with an increased risk of psychosis, possibly by interacting with a pre-existing vulnerability for these disorders. A dose-response relationship was found between cannabis exposure and risk of psychosis, and this association was independent from potential confounding factors such as exposure to other drugs and pre-existence of psychotic symptoms. However, the diagnostic specificity is weak, as cannabis exposure may be a risk factor for the occurrence of a large spectrum of psychiatric disorders, ranging from schizophrenia to mood and anxiety disorders.

CONCLUSION: Considering the growing number of adolescents exposed to cannabis, the impact of this substance on the population mental health should be further explored.