Background: In recent years, cannabis has been increasingly discussed as one of the most important environmental risk factors for developing schizophrenic psychoses. This is mainly due to the following observations. (i) Cannabis at high doses can cause acute transient psychotic symptoms even in healthy individuals. (ii) Patients with schizophrenia abuse cannabis more often than age-matched healthy controls.
Objectives: It is still controversial whether cannabis use can cause schizophrenic psychoses that would not have occurred otherwise. In our review, we have critically evaluated the evidence for a causal link between cannabis use and schizophrenic psychoses.
Methods: A systematic literature review in PubMed, ISI Web of Science and PsycINFO was carried out using the following keywords: cannabis, marijuana, THC, hashish, psychosis, schizophrenia.
Conclusions: We have concluded that although a causal relationship between cannabis use and schizophrenic psychoses cannot be definitely proven, the available evidence strongly supports its plausibility. Furthermore, the results of the review indicate that cannabis might cause psychosis especially in individuals with a predisposition for schizophrenia and in adolescents with an early onset of cannabis use.
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