Cannabis and Schizophrenia: Blowing Smoke?

Rates of cannabis use among patients with schizophrenia have been estimated to be at least twice those of the general population, and most reports have associated heavy cannabis use with increased risk for developing psychotic symptoms. However, uncertainties remain: Does this risk primarily affect individuals with underlying vulnerabilities for developing schizophrenia? Do patients who develop schizophrenia in the context of heavy cannabis use differ clinically from non–cannabis-using patients with schizophrenia?

These investigators retrospectively examined lifetime clinical characteristics of 455 patients with schizophrenia or schizoaffective disorder, 175 of whom had histories of comorbid cannabis abuse or dependence. Neurocognitive tests…