Observational studies have consistently shown that recreational cannabis use is associated with an increased risk of psychosis — a condition that can cause delusions and hallucinations, making it challenging to determine what is reality. While observational studies can’t determine whether cannabis causes psychosis (as opposed to psychosis leading people to use cannabis), the current evidence seems to suggest it. If so, THC is the likely culprit.
Multiple longitudinal cohort studies around the world have generated similar results, finding a dose-dependent relationship between cannabis use and the development of psychosis, even when controlling for multiple confounders.[1][2][3][4][5] Additionally, the relationship does not seem to be influenced by whether someone has a history of psychotic symptoms.[6]
The risk of psychosis seems to be influenced by a number of factors, including the use of higher-potency cannabis (containing higher doses of THC), exposure early in life (i.e., adolescence), long-term cannabis use, and a family or personal history of psychosis.[7][1] Interestingly, a gene variant that influences how dopamine is metabolized in the brain has been linked to an increased risk of psychosis in adolescents exposed to cannabis.[8]