This study compared the safety and withdrawal discomfort associated with transitioning pregnant opioid-dependent women from short-acting morphine onto buprenorphine or methadone under well-controlled double-blind conditions. Participants (n=18) were patients in a comprehensive treatment setting and were part of a larger randomized controlled trial comparing the neonatal abstinence syndrome in mothers treated with individualized doses of sublingual buprenorphine or oral methadone. Methadone was first given to all patients within 24h of treatment admission. After written informed consent was signed (3-5 days post-admission), methadone was discontinued and Immediate Release Morphine (IRM) was initiated. The initial total daily dose of IRM was six times the last daily methadone dose. The daily dose of IRM was divided in four daily doses. Induction onto double-blind, double dummy (i.e., two medications were administered with only one being active) methadone or buprenorphine was accomplished over 3 days (i.e., induction). Withdrawal scores during the IRM and induction onto randomized medication were judged mild and not statistically different for both methadone (mean dose 53.5 mg) and buprenorphine (mean dose 10.9 mg). No significant differences between medication groups were observed when individual withdrawal items were examined. No observed differences in safety measures including fetal movement, maternal physiological parameters of body temperature, heart rate and blood pressure were observed between groups. Transitioning opioid-dependent pregnant women from IRM to methadone or buprenorphine during the second trimester of pregnancy can be conducted with similar comfort and safety.