Variance of Oral Methadone Dosage: Description of Implicated Factors

The purpose of this study is to describe clinical, pharmacokinetic and genetic factors associated with the variance of oral methadone dosage for patients at the steady state of heroin dependence maintenance treatment. The hypothesis is that the investigators can predict 70% of the variance with few factors, including CYP 3A4 function measured with oral midazolam challenge.