Originally posted by TheTripDoctor:
The route which codeine is converted to morphine in the body is though an enzyme, CYP2d6 specifically, at a rate of 10% in a normal person.
This conversion can be either inhibited or increased, though the use of Enzyme inducers or inhibitors. All of the fairly usefull drugs which have the inducing action are restricted, meprobamate is one, glutethimide is the most popular though and was used with codeine in place of a morphine based opiate in many cases on the street. Promethazine appears to have this effect as well though i dont know offhand if its due to CYP2d6 or another mechanism.
This idea is basically a lost cause, because if you can get any amount of the chemicals that induce the enzyme, you can probably also get a real opiate just as easily.
If mepobromate is one of the enzyme inducers, then it is fairly easy to get online, AND, soma is metabolized into mepobromate, which could explain the popularity of the soma/opiate combos.