The prevention of seclusion and other coercive measures has become a priority for mental health facilities, and numerous comprehensive programs to reduce the use of these containment procedures, have been developed. It is, however, poorly understood which interventions or elements of programs are effective and by which mechanisms or processes change is mediated. The present study explores the effects of an intervention by which a reduction in the use of seclusion was achieved. The intervention concerned a transformation of the treatment process, based on the principles of the methodical work approach, at a ward for the intensive treatment of patients with psychosis and substance use disorders. Changes in the working practice and team process were analyzed on the basis of case examples and team evaluation. The methodical work approach appears to have provided a guidance for the multidisciplinary team, the patient and the family to work together in a systematic and goal-directed way with cyclic evaluation and readjustment of the treatment and nurse care plan. Also implicit, positive changes were found in the team process: increased interdisciplinary collaboration, team cohesion, and professionalization. It is argued that the implicit or non-specific effects of an intervention to prevent seclusion may constitute a major contribution to the results and therefore merit further research.