Time trends in co-occurring substance use and psychiatric illness (dual diagnosis) from 2000 to 2017 – a nationwide study of Danish register data

Abstract

Objective

This article aims to describe the time trend in number of dual diagnosis patients treated in the psychiatric system in Denmark from 2000 to 2017.

Method

We calculated the share of patients with dual diagnosis, number of dual diagnosis contacts, number of unique individuals with dual diagnosis as well as number of new patients with dual diagnosis among patients in psychiatric treatment, i.e. among inpatients, outpatients and patients in emergency departments. In order to calculate this, we merged data from the National Patient Register (NPR), the National Registry of Alcohol Treatment, the National treatment registry for substance use, the National Prescription Registry and the Danish National Health Service register in the period from 2000 to 2017.

Results

We found an overall increase in patients with dual diagnosis in psychiatric treatment in Denmark from 2000 to 2017. We further detected an increase in the age and sex-standardized number of patients with dual diagnosis in treatment over time, however most markedly for outpatients. Further, inclusion of data from other sources of data than the NPR dramatically increased the number of patients that could be identified as dual diagnosis patients. Using these data, almost half of all male inpatients could be identified as dual diagnosis while the share was more than 40% for patients with schizophrenia, schizotypal and delusional disorders (F2) and patients with personality disorders (F6).

Conclusions

The increase of individual diagnosis patients necessitates action at different levels. This includes improvement of preventive measures as well as improvement of treatment for this underserved group.

Keywords:

• Dual diagnosis
• substance use disorder
• epidemiology
• psychiatry
• schizophrenia

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The cohort is funded by the Research Committee, Psychiatric Center Sct. Hans, the Muusfeldt Foundation [grant number 2017-871], Helsefonden [grant number 19-A-0042].