Objective Common mental disorders are a major concern in working populations due to their high prevalence and as a barrier to remaining healthy and productive at work. Patients with common mental disorders often suffer from comorbidities, which may limit their functioning at work. We assessed the longitudinal impact of multimorbidity, defined as two or more co-occurring chronic health conditions, on work functioning among workers who had returned to work after sick leave due to a common mental disorder.

Methods Prospective cohort study of 156 workers followed for one year after return to work from sick leave due to a common mental disorder. A multimorbidity score was computed by counting severity-weighted chronic health conditions measured at baseline. Work functioning was measured at baseline and at 3, 6 and 12 months follow-up with the Work Role Functioning Questionnaire. Work functioning trajectories were identified using latent class growth analysis to investigate the effect of multimorbidity on the course of work functioning scores.

Results A total of 44% workers had multimorbidity. Four work functioning trajectories were identified: one (12% of the workers) showed increasing work functioning scores during follow-up, whereas the other three trajectories showed stable low, medium and high scores (23%, 41% and 25% workers, respectively). Multimorbidity did not predict membership probability in any trajectory. However, within the increasing score trajectory, levels of work functioning were lower among those with a high baseline multimorbidity score; each one unit increase in multimorbidity implied a reduction of 1.4 points in the work functioning score (p > 0.001).

Conclusions Multimorbidity has a negative impact on workers’ perception of work functioning after returning to work from a sick leave due to a common mental disorder.