Purpose: To compare the prevalence and pattern of comorbid substance use disorders (SUD) between patients with schizophrenia, bipolar disorder, and depressive illness.
Methods: Data on presence of alcohol use disorder (AUD) and non-alcohol drug use disorder (DUD) were retrieved from the Norwegian Patient Register for individuals born between 1950 and 1989 who in the period 2009-2013 were diagnosed with schizophrenia, bipolar disorder or depressive illness according to the 10th version of the WHO International Classification of Diseases. The prevalence of AUD only, DUD only, or both was compared between men and women across age and diagnostic groups.
Results: The prevalence of SUD was 25.1 % in schizophrenia (AUD: 4.6 %, DUD: 15.6 %, AUD and DUD: 4.9 %), 20.1 % in bipolar disorder (AUD: 8.1 %, DUD: 7.6 %, AUD and DUD: 4.4 %), and 10.9 % in depressive illness (AUD: 4.4 %, DUD: 4.3 %, AUD and DUD: 2.2 %). Middle-aged men with bipolar disorder had the highest prevalence of AUD (19.1 %) and young men with schizophrenia had the highest prevalence of DUD (29.6 %). Of the specific DUDs, all but sedative use disorder were more prevalent in schizophrenia than the other groups. Cannabis and stimulant use disorder was found among 8.8 and 8.9 %, respectively, of the men with schizophrenia.
Conclusions: The alarmingly high prevalence of DUD among young patients with severe mental disorders should encourage preventive efforts to reduce illicit drug use in the adolescent population.