PURPOSE: The present study established the national prevalence of substance use disorders (SUDs) among Danish psychiatric patients. Furthermore, patients with SUDs and those without SUDs were compared on a range of socio-demographic, clinical, and treatment characteristics.

METHODS: Data were obtained from several Danish population-based registers. The study population was defined as all individuals with incidents of schizophrenia, schizotypal disorder, other psychoses, bipolar disorder, depression, anxiety, obsessive-compulsive disorder (OCD), post-traumatic stress disorder (PTSD), and personality disorders since 1969. The prevalence of SUDs was examined for the following psychoactive substances: alcohol, opioids, cannabis, sedatives, cocaine, psycho-stimulants and hallucinogens.

RESULTS: A total of 463,003 patients were included in the analysis. The prevalence of any lifetime SUD was: 37 % for schizophrenia, 35 % for schizotypal disorder, 28 % for other psychoses, 32 % for bipolar disorder, 25 % for depression, 25 % for anxiety, 11 % for OCD, 17% for PTSD, and 46 % for personality disorders. Alcohol use disorder was the most dominating SUD in every psychiatric category (25 % of all included patients). Patients with SUDs were more often men, had fewer years of formal education, more often received disability pension and died due to unnatural causes.

CONCLUSIONS: The study was the most comprehensive of its kind so far to estimate the prevalence of SUDs in an unselected population-based cohort, and it revealed remarkably high prevalence among the psychiatric patients. The results should encourage continuous focus on possible comorbidity of psychiatric patients, as well as specialised and integrated treatment along with increased support of patients with comorbid disorders.