The present work answers to a call for proposals made by the Belgian Federal Science Policy Office, within the framework of a research program supporting the federal policy document on addictive drugs. The main objective of this research was the assessment of the effectiveness1 and the efficiency2 of opiates addiction treatments using substances that could mimic the effects of street heroin. Such treatments are called substitution treatments in Belgium. Their goal is twofold : first, to get the patients into the treatment network and two, to have them remain within it as long as the medical-social-psychological-judicial situation preceding inclusion in the next stage of treatment isn’t satisfactory enough. These are imperative conditions in order to maintain full abstinence in the future (Reggers et Ansseau, 2000) and the first stage of treatment is abstinence from street drug, i.e. heroin. The impact of psychosocial support and adjuvant treatments were also evaluated in this work.