This review examines two hypotheses linking cannabis use to psychosis. The first, that heavy cannabis use can cause a distinct 'cannabis psychosis' that would not otherwise occur, has limited clinical support; such cases appear rare and likely require very high tetrahydrocannabinol doses, prolonged use of potent cannabis, or a preexisting vulnerability. The second hypothesis, that cannabis use may precipitate or worsen schizophrenia, has more backing: one large prospective study found a linear relationship between cannabis use frequency by age 18 and schizophrenia diagnosis risk over 15 years. However, it remains unclear whether cannabis precipitates schizophrenia, represents self-medication, or if other drug use explains the association. Cannabis use can exacerbate schizophrenia symptoms.
This review examines two hypotheses linking cannabis use to psychosis. The first posits that heavy cannabis use may cause a rare 'cannabis psychosis' that remits after abstinence, requiring very high THC doses, prolonged use of potent cannabis, or a pre-existing vulnerability. The second suggests cannabis may precipitate or exacerbate schizophrenia. A large prospective study found a linear relationship between cannabis use frequency by age 18 and schizophrenia risk over 15 years, though causality remains unclear due to possible confounding by other drug use or self-medication. Stronger evidence supports that cannabis exacerbates schizophrenia symptoms. Mental health services should identify and advise patients with schizophrenia to reduce or abstain from cannabis and other drugs.