In France, during the 1990s, there have been some rapid developments in the treatment of opioid addiction with the introduction of legal substitution agents. Originally, some patients were treated with morphine sulfate, but this was superseded by high dose buprenorphine (Subutex®) and methadone. This resulted in those patients originally treated with morphine being transferred to either of these two licensed products. A study investigating the effects of the transition from morphine to either buprenorphine or methadone was undertaken. Supplementary to this, a trial investigating transition between these new compounds was also conducted. The primary outcome measures for these trials were retention rate, which was assessed at 5, 9 and 12 months, and the precipitation of withdrawal symptoms. The studies showed that transferring patients between substitution agents can be accomplished without severe withdrawal symptoms, although specific management may be required for transfer from high doses of methadone to buprenorphine. High long-term retention rates were observed in the studies, with most drop-outs occurring directly after transfer. Results suggest that patients on long-term buprenorphine maintenance therapy may have good compliance in comparison with other agents.