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The complex relationships between cannabis and psychosis have been the subject of a number of studies in the last twenty years. Cannabis can induce transient psychotic-like symptoms in up to 15 % of users, symptoms that disappear with the elimination of Δ9-THC from the body. Several studies have found that cannabis also doubles the risk of psychotic disorders, in particular schizophrenia. The risk is even higher if cannabis use started at an early age, if it is consumed in large amounts, if it contains a high level of Δ-9-THC, if there is a family history of psychotic disorders, susceptible genetic factors, and a history of abuse in childhood.In schizophrenia patients, cannabis use is very common, and in patients experiencing their first psychotic episode, one third also present an abuse of or dependence on alcohol or drugs. Cannabis abuse is associated with more severe psychotic symptoms, worse medication adherence, more frequent relapses, rehospitalizations, and a greater risk of aggression, depressive symptoms, and suicidal behaviors. Meanwhile, those who stop using cannabis experience improvements in these domains. Results are better among first-episode patients who stopped using substances when compared to similar first-episode patients who continued substance use. Therefore, it is important to treat patients as early as possible and integrate a motivational approach to addiction into their psychiatric treatment.