Study Status: Completed
Recruit Status: Completed
Study Type: Observational
Official Title: Factors Associated With the Variance of Oral Methadone Dosage at Steady State of Maintenance Treatment: Description of Bio-markers of Phenotype and Genotype.
Brief Summary: 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.