Is 'cannabis psychosis' a distinct category?

Forty-five cases of psychotic patients with admission urinalysis positive for cannabis were compared with psychotic controls without evidence of cannabis use. Cases and controls were matched for age, sex and year of admission, and were compared for socio-demographic data, circumstances of admission, diagnosis, and symptoms at admission. Three differences were found: cases were more likely to be Afro-Caribbean than white (P = 0.01), to manifest incoherence of speech (P = 0.02) and agitation (P = 0.01). In other respects the case and control groups were indistinguishable, and no pattern of symptoms characterised the 'cannabis psychosis' group. These findings do not support the view that 'cannabis psychosis' has a distinct psycho-phenomenological pattern. Epidemiological studies are required to further clarify the association for psychotic patients between Afro-Caribbean ethnic groups and the likelihood of having a positive urine test for cannabis.