Cannabis psychosis and acute schizophrenia. a case-control study from India.

Twenty cases of cannabis psychosis were compared with a control group of 20 patients with 'acute schizophrenic episode' on a number of demographic, clinical, illness-related and outcome variables in a case-control study design using a retrospective chart review. The two groups were comparable on demographic, past and family histories of mental illness, premorbid personality, psychomotor activity, Schneiderian first-rank symptoms and mild cognitive deficits. The cases, in contrast to the control group, had a psychosis of shorter duration characterized by reactive and congruent affect, relative absence of schizophrenic formal thought disorder and a predominantly polymorphic clinical picture. Relapse was always preceded by cannabis use. This study suggests that, in spite of certain overlaps, 'cannabis psychosis' may still be considered nosologically distinct from schizophrenia in India. The implication of the study is that the role of cannabis in any acute psychosis should be investigated carefully so as to prevent an overdiagnosis of schizophrenia.