Since 2015 slow-release oral morphine (SROM) is approved for opioid substitution treatment (OST) in Germany. The SROMOS study (efficacy and tolerability of slow-release oral morphine in opioid substitution treatment) evaluates the efficacy and safety of SROM in routine care. This article describes the switching process from racemic methadone, levomethadone and buprenorphine to SROM. Between July 2016 and November 2017 180 patients in 23 study centers in Germany were included in the prospective, non-interventional, naturalistic observational study. Patients were already in OST and switched from a previous medication to SROM. The switching process was analyzed during a period of fourteen days. Data were available for 169 participants. The switching process had a different progression depending on premedication and pre dosage. On the fourteenth day of SROM treatment patients switched from racemic methadone took an average dosage of 922.2 mg/day, from levomethadone 801.0 mg/day and from buprenorphine 626.7 mg/day. Average conversion ratio racemic methadone to SROM was 1:11.8, levomethadone to SROM 1:17.4 and buprenorphine to SROM 1:58.0. This study provides the first data on the switching process from buprenorphine to SROM. Average dose ratio racemic methadone to SROM on the fourteenth day of treatment was considerably higher than recommended in the prescribing information.