Opioid Agonist Therapy (OAT) for opioid dependency Abstract. The process of evaluating the necessity of an Opioid Agonist Therapy (OAT) is relatively simple. Once the criteria for an opioid dependency according to the ICD-10 (or DSM V) are met, treatment should be offered. Adequate individual dosing of the opioid agonist is crucial to treatment success. Several equally effective opioids are available. Comorbidities are common and should be taken into account when planning and conducting an OAT. In this article the State-Of-The-Art of the OAT will be presented, focusing upon the German-speaking European countries. The article provides an overview of diagnosis, treatment modalities, drug therapy and some specific challenges of the OAT. Treatment recommendations are in accordance with the Swiss model, hence adaptations to treatment due to local state laws may be necessary in other countries.