This review examines the evidence for a causal relationship between cannabis use and psychosis, particularly schizophrenia. The authors analyze five studies that used population-based data and prospective measures of cannabis use and adult psychosis. They find that cannabis use is associated with an increased risk of later schizophrenia, with an overall twofold increase in relative risk. At the population level, eliminating cannabis use could reduce schizophrenia incidence by about 8%, assuming a causal relationship. Cannabis is not a sufficient or necessary cause for psychosis but is a component of a complex set of factors leading to psychosis. The review discusses the criteria for causality, including association, temporal priority, and direction. Evidence for association includes higher rates of cannabis use among individuals with schizophrenia and those with psychosis. Temporal priority is supported by studies showing that cannabis use precedes the onset of schizophrenia. Direction is indicated by the persistence of the association even after controlling for confounding variables. The Swedish conscript cohort study found a dose-response relationship between cannabis use and schizophrenia diagnosis. The Dutch NEMESIS study found that cannabis use was associated with an increased risk of psychotic symptoms, with a dose-response relationship. The Christchurch study found that cannabis dependence was associated with an increased risk of psychotic symptoms. The Dunedin study found that cannabis use in adolescence was associated with an increased risk of schizophrenia in adulthood. The review also discusses methodological limitations, including the use of self-reported data and the difficulty in establishing temporal priority. It notes that cannabis use is not a necessary or sufficient cause for psychosis but is a contributing factor. The review concludes that cannabis use may be a causal factor in the development of psychosis, particularly in vulnerable individuals. It emphasizes the need for further research to understand the mechanisms by which cannabis causes psychosis and to develop strategies to prevent cannabis use among vulnerable youth.This review examines the evidence for a causal relationship between cannabis use and psychosis, particularly schizophrenia. The authors analyze five studies that used population-based data and prospective measures of cannabis use and adult psychosis. They find that cannabis use is associated with an increased risk of later schizophrenia, with an overall twofold increase in relative risk. At the population level, eliminating cannabis use could reduce schizophrenia incidence by about 8%, assuming a causal relationship. Cannabis is not a sufficient or necessary cause for psychosis but is a component of a complex set of factors leading to psychosis. The review discusses the criteria for causality, including association, temporal priority, and direction. Evidence for association includes higher rates of cannabis use among individuals with schizophrenia and those with psychosis. Temporal priority is supported by studies showing that cannabis use precedes the onset of schizophrenia. Direction is indicated by the persistence of the association even after controlling for confounding variables. The Swedish conscript cohort study found a dose-response relationship between cannabis use and schizophrenia diagnosis. The Dutch NEMESIS study found that cannabis use was associated with an increased risk of psychotic symptoms, with a dose-response relationship. The Christchurch study found that cannabis dependence was associated with an increased risk of psychotic symptoms. The Dunedin study found that cannabis use in adolescence was associated with an increased risk of schizophrenia in adulthood. The review also discusses methodological limitations, including the use of self-reported data and the difficulty in establishing temporal priority. It notes that cannabis use is not a necessary or sufficient cause for psychosis but is a contributing factor. The review concludes that cannabis use may be a causal factor in the development of psychosis, particularly in vulnerable individuals. It emphasizes the need for further research to understand the mechanisms by which cannabis causes psychosis and to develop strategies to prevent cannabis use among vulnerable youth.