Background. Past studies have found inconsistent evidence that substance use disorders are related to earlier onset of schizophrenia or more severe symptoms. This study examines prevalence and severity of current substance use disorders and onset of psychotic illness in a multi-facility sample.

Methods. Data are from the Suffolk County Mental Health Project, an epidemiological study of first admission psychosis. The SCID and instruments measuring symptomatology, personality and background characteristics were administered. Respondents were stratified into three groups: (a) no life-time substance diagnosis; (b) in remission or reporting current mild use at admission; and (c) current moderate–severe substance abuse at admission.

Results. Using the SCID severity rating, 17·4% of males and 6·2% of the females had moderate or severe current substance abuse, while 41·5% of males and 68·2% of females had no lifetime substance diagnosis. In almost all cases categorized as moderate–severe, the substance diagnosis predated onset of psychosis. Females categorized as moderate–severe had an earlier age of onset of psychosis than did females in the other groups. There were only slight differences in symptom severity among the groups but more marked antisocial behaviour in the moderate–severe group. Variables discriminating the moderate–severe from non-abuse groups were BPRS thought disturbance, adult anti-social behaviour and current cigarette smoking for males and adult antisocial behaviour and child–teen antisocial behaviour for females.

Conclusions. Severity of substance abuse does not appear to be a pivotal correlate of the early features of psychotic illness.