Cannabis use in a large sample of acute psychiatric admissions.

A sample of 908 patients drawn from two London Psychiatric Hospitals is described in terms of age, sex, self-reported drug and alcohol history, drug urinalysis results and initial psychiatric diagnosis. Some (34.5%) of respondents admitted to using cannabis at least once in their lifetime and 13% of those tested had urines positive for cannabis on admission. Cannabis use is commoner in young males. These is a higher likelihood that an initial diagnosis of 'psychosis' will be made at admission if patients either report use of cannabis or present a urine sample positive for cannabis.