Alcohol use and daily smoking are common among individuals with schizophrenia spectrum disorder but less is known about their relationship to psychotic symptom profile and severity, and how clozapine use may affect this relationship.

Among a clinical sample of 276 Finnish outpatients with schizophrenia spectrum disorder (68.8% schizophrenia), the Brief Psychiatric Rating Scale (BPRS) and the Scale for the Assessment of Negative Symptoms (SANS) were used to determine severity of psychotic symptoms. Information regarding alcohol use was collected with questionnaires including the Alcohol Use Disorders Identification Test-Concise (AUDIT-C) and information of smoking. Associations between psychiatric symptoms and substance use were studied using linear regression separately for those with or without clozapine use. Age, gender, marital status, living situation and education were adjusted for in the final analyses.

In the multivariable models, heavy alcohol use and binge drinking were less frequent among participants with clozapine use (n = 115) compared to those without (n = 161). Differences in some symptoms were observed in bivariate analyses when comparing the participants with and without heavy or binge drinking, or daily smoking. Heavy and binge drinking were associated with more severe grandiosity symptoms even after controlling for potential confounders. Daily smoking was associated with more severe hostility, elated mood, unusual thought content and uncooperativeness, but less severe emotional withdrawal.

Symptom profiles and severity differed according to alcohol use or smoking. The possible explanations for the role of clozapine are discussed.