Substance use disorders in New Zealand adults with severe mental illness: descriptive study of an acute inpatient population

Objective: To elucidate patterns of substance misuse, across diagnoses and demographic variables, in patients with severe mental illness. Method: We studied 141 adults admitted to an acute psychiatric unit in Hamilton, New Zealand. Semi-structured interviews, including the Alcohol Use Disorders Identification Test (AUDIT) and Cannabis Use Disorders Identification Test - Revised (CUDIT-R), were used to assess substance use. Results: Seventy-six participants were of European origin (56%), 59 were Maori (42%). Tobacco smoking was noted in 81% overall, with a higher frequency (93%) among Maori. A majority of patients had alcohol use disorder, with greater prevalence in bipolar and schizoaffective disorder compared to schizophrenia. By contrast, cannabis use disorder was strikingly associated with schizophrenia. Younger patients and Maori were disproportionately affected by both alcohol and cannabis use. Conclusions: Substance misuse in New Zealand patients with severe mental illness is common, particularly among younger patients and Maori, and differentially distributed across diagnoses.