The prevalence and comorbidity of mental health and substance use disorders in Scandinavian prisons 2010-2019: a multi-national register study.

Background: Mental health disorders are common among people in prison, but their prevalence in the Scandinavian prison population remain unclear. In this multinational register study, we examined the prevalence of mental health disorders and the comorbidity of substance use disorders (SUDs) with other mental health disorders in this population. Further, we investigated how the prevalence of mental disorders at prison entry had changed in Norway, Denmark, and Sweden over the study period.

Methods: The three study cohorts included all individuals, aged 19 or older, whom had been imprisoned in Norway (2010-2019), Denmark (2011-2018), and Sweden (2010-2013). Mental disorders were defined as ICD-10 diagnoses (F-codes) registered in the national patient registers. The study prevalence was estimated based on recorded diagnoses during the entire study follow-up period in each respective country. The one-year prevalence of mental disorders was estimated for each calendar year for individuals entering prison during that year.

Results: The Scandinavian prison cohorts included 119 507 individuals released 191 549 times during the study period. Across all three countries a high proportion of both women (61.3%-74.4%) and men (49.6%-57.9%) had at least one mental health disorder during the observation period. The most prevalent disorders were SUDs (39.1%-44.0%), depressive disorder (8.1%-17.5%), and stress related disorder (8.8%-17.1%). Women (31.8%-41.1%) had higher levels of mental health and substance use comorbidities compared to men (20.8%-27.6%). The one-year prevalence of any mental health disorder increased over time with a 33% relative increase in Norway, 8% in Denmark, and 10% in Sweden. The proportion of individuals entering prison with a comorbid SUD and other mental disorder had also increased.

Conclusions: While the incarceration rate has been decreasing during the past decade in the Scandinavian countries, an increasing proportion of people entering prison have a diagnosed mental health disorder. Our results suggest that prisons should provide adequate treatment and scale up services to accommodate the increasing proportion of people with complex health needs among incarcerated people.