Psychotherapy and change in mental health-related work disability: a prospective Finnish population-level register-based study with a quasi-experimental design

BACKGROUND: Mental disorders are a major cause of work disability among the working-age population. Psychotherapy has shown to be an effective treatment for mental disorders, but the evidence is mainly based on small-scale randomised trials with relatively short follow-ups. We used population-based register data to examine the association between statutory rehabilitative psychotherapy and change in depression or anxiety-related work disability. METHODS: We drew a nationally representative sample of the working-age population (aged 18–55 in 2010). The study group comprised all those who started rehabilitative psychotherapy in 2011–2014. A total of 10 436 participants who were followed from 3 years prior to 4 years after the onset of rehabilitative psychotherapy. This resulted in 83 488 observations. The annual total number of mental health-related work disability months (0 to 12) was calculated from the total number of annual compensated sickness absence and disability pension days. A quasi-experimental interrupted time series analysis was applied. RESULTS: The onset of rehabilitative psychotherapy marked a decline in work disability in comparison to the counterfactual trend. Specifically, a 20% decrease in the level (incidence rate ratio, IRR 0.80; 95% CI 0.76 to 0.85) and a 48% decrease in the slope (IRR 0.52; 95% CI 0.50 to 0.54) of work disability were detected in comparison to the counterfactual scenario. No significant gender differences were observed. The decline in work disability was the steepest in the oldest age group. CONCLUSIONS: This study suggests that statutory psychotherapy may decrease work disability at the population level. However, further evidence of causal inference and the potential heterogeneity of the association is required.