These practice guidelines for the biological treatment of substance use disorders were developed by an international Task Force of the World Federation of Societies of Biological Psychiatry (WFSBP). The goal during the development of these guidelines was to review systematically all available evidence pertaining to the treatment of substance use disorders, and to reach a consensus on a series of practice recommendations that are clinically and scientifically meaningful based on the available evidence. These guidelines are intended for use by physicians evaluating and treating people with substance use disorders and are primarily concerned with the biological treatment of adults suffering from substance use disorders. The data used to develop these guidelines were extracted primarily from various national treatment guidelines for substance use disorders, as well as from meta-analyses, reviews and randomized clinical trials on the efficacy of pharmacological and other biological treatment interventions identified by a search of the MEDLINE database and Cochrane Library. The identified literature was evaluated with respect to the strength of evidence for its efficacy and then categorized into four levels of evidence (A-D). This first part of the guidelines covers the treatment of alcohol dependence; Part 2 will be devoted to the treatment of drug dependence.