Formulations: theories vs. experience

Strictly from a pharmacological standpoint one might believe that a racemic mixture, half active and half ostensibly inactive, would have identical effect except that one needs twice the concentration of the racemate to procude equal results to the pure active form. For years most experts believed the "pure" form of methadone (almost exclusively used in Germany) was identical to the d/l form used in the rest of the word except it was twice as potent. But it is not so simple - a recent article in Dug Alc Dependence by Verthein and colleagues (2005, vol. 80) suggests there are differences, and withdrawal when switching from one form to the other - though the effects are of a transient nature only