Cannabis use has been related to many psychiatric problems, particularly psychotic disorders, affective disorders, and anxiety. Chronic cannabis use is related to panic attacks, anxiety, depression, and low motivation. It would appear that frequent cannabis use during adolescence is predictive of later depression and anxiety. Cannabis has also been related to amotivational syndrome in chronic users. This disorder is characterized by a personal deterioration with loss of energy and work drive, but the validity of this syndrome remains uncertain. Epidemiological studies have shown a clear association between cannabis use and psychosis, mainly adult schizophreniform disorders. Recent studies have identified a higher frequency of disturbance in sensorium, irritability, affective disturbances, derealization/depersonalization, and visual hallucinations in cannabis induced psychosis than in acute schizophrenia psychosis. Schizophrenia with substance abuse has been associated with poor treatment compliance, increased rates of hospital admissions, suicide, violent behavior and unstable housing and homelessness. Cannabis use specifically has been correlated with the exacerbation of psychotic symptoms and increased tardive dyskenisia. It may be the case that schizophrenic patients are inclined to consume cannabis, either due to lowered impulse control or as a means of reducing negative symptoms. On the other hand, it may be that cannabis use itself either causes of precipitates psychosis. In short, the association between cannabis use, psychosis, depression, behavioral problems, tobacco smoking, excessive drinking and use of illicit drugs shows a severe pattern of comorbidity that may lead to further negative outcomes, and requires further study for the identification of appropriate treatments.