While there is increasing evidence on the association between cannabis use and schizophrenia, it is still unclear whether schizophrenia patients with a cannabis history have another prognosis, with regard to relapse and hospital duration, compared to those without a cannabis history.

A cohort study of 50000 Swedish men with data on cannabis use at ages 18–20. A total of 350 cases of schizophrenia were identified from inpatient care records and followed up from 1970 through 2010. Records of schizophrenia patients with and without a history of cannabis use were investigated with regard to types of diagnoses, duration of first admission, rate of re-admission and total duration of hospital stay.

Schizophrenia patients with history of cannabis use had a higher median duration of first hospital episode (59 days vs 30 days). Patients with a history of cannabis had a higher median rate of re-admission (10 times vs 4 times). Also total number of hospital days was higher in patients with cannabis history compared to those without (547 days vs 184 days) The distribution of types of schizophrenia was difficult to assess since many received a “unspecified” diagnosis, and there was no significant difference between the groups.

Schizophrenia patients with history of cannabis used had significantly higher burden of inpatient care than non cannabis users. Not only does cannabis increase the risk of schizophrenia, but our findings indicate that the type of schizophrenic psychosis may be more severe than schizophrenia cases in general.