This study compared two groups of patients admitted to SUD and psychiatry wards: those admitted involuntarily (IA group) and those admitted voluntarily (VA group). Patients in the IA group were recruited from three publicly funded treatment centres in the south-eastern part of Norway. These centres are located in Kristiansand, Tønsberg, and Oslo, and they have four, four, and three beds, respectively, for patients admitted involuntarily. All patients in the VA group were from a single ward in the Kristiansand centre. The three wards are organized quite similarly. They all treat patients of both genders, but most patients were males. The patients may spend time in communal areas, but the exterior doors are locked. Most patients are allowed to leave the ward, when accompanied by a representative from the staff. Many patients received visits from friends and family. Both as a routine procedure and due to suspicion, the patients are required to undergo a urine test for drug-screenings. All wards were multidisciplinary (psychiatrists, psychologists, social workers, occupational therapists, specialized nurses, and other trained staff) and had specialized units that offered treatment for patients with primary SUD combined with mental disorders, a combination which is often observed. Treatment included assessments of somatic and mental health; diagnoses, based on a structured interview and examination, consistent with the International Classification of Diseases and Related Health Problems, 10th Revision (ICD-10); pharmacotherapy; cognitive milieu therapy; and individual motivation enhancement. The patient population was recruited mainly from urban and suburban areas.