Abstract
OBJECTIVES: Sickness absence due to mental disorders is increasing in many high-income countries, yet the impact of routine mental health treatment on work disability outcomes remains unclear. This study examined trajectories of work disability (working, partly or full sick leave, Work Assessment Allowance, or disability pension) before and after routine mental health care and identified factors associated with work disability status. METHODS: A prospective cohort of 2,609 adult outpatients with mild to severe mental disorders receiving routine mental health treatment in Norwegian community or specialist services was followed. Registry data tracked work disability status one year before and after treatment. Group-based trajectory modelling, sequence clustering, and multinomial logistic regression were used. RESULTS: Work disability increased sharply in the year prior to treatment, peaking at 38% at treatment start. Although a modest decline in absenteeism followed, long-term medical benefits of Work Assessment Allowance steadily rose from 7% pre-treatment to 18% post, a 152% increase, contributing to sustained levels of absenteeism after start of treatment. Five trajectories were identified, with 46% maintaining stable work ability. Approximately 30% of patients, corresponding to clusters 3 and 4, experienced reduced sick leave with benefit transition to long-term medical benefits, while 7% were permanently on disability pension. Older age, female sex, and treatment in specialist services were associated with higher work disability, while community services targeting mild to moderate conditions were linked to better work ability outcomes. CONCLUSIONS: Work disability increased sharply before treatment and remained persistently high throughout the following year, forming a plateau across care levels. Although nearly half of the patients maintained stable work ability, the findings indicate that routine mental health care, especially specialist services, may have limited effectiveness in preventing long-term work disability. A substantial proportion transitioned into long-term medical benefits, highlighting the urgent need for timely interventions that integrate work ability as a core treatment objective and apply targeted interventions to enhance it. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12913-025-12856-w.