Long-term sick leave due to common mental disorders (CMD) is an increasing problem in many countries. Recent reviews indicate that return to work (RTW) interventions have limited effect on reducing sickness absence among this group of sick-listed. The aims of this study were to investigate how sick-listed persons with CMD experienced participating in an RTW intervention and how workability assessments and RTW activities influenced their RTW-process, and to examine the working mechanisms of the intervention. The gained knowledge can help improve future RTW intervention design and implementation.In-depth interviews were conducted with 17 participants on sick leave due to CMD who participated in an RTW intervention. Interviews were conducted at three time points with each participant. Principles of interpretative phenomenological analyses guided the analysis.The workability assessment consultations and RTW activities such as psychoeducative group sessions and individual sessions with psychologist could result in both motivation and frustration depending on the extent to which the RTW professionals practiced what we have termed an individual approach to the sick-listed person.The individual approach seems necessary for the realization of the positive potential in the RTW intervention. However, the fact that RTW professionals are both the facilitators and the controllers of the sick-listed persons' RTW process is an inherent paradox in the intervention, which can impede the necessary establishment of a high-quality relationship between the sick-listed persons and RTW professionals.