This report presents the recommendations of the thirty-ninth WHO Expert Committee on Drug Dependence (ECDD). The ECDD is responsible for the assessment of psychoactive substances for possible scheduling under the international drug control conventions. The ECDD reviews the therapeutic usefulness, the liability for abuse and dependence, and the public health and social harm of each substance. The ECDD will advise the Director-General of WHO, to schedule or to amend the scheduling status of a substance. The Director General will, as appropriate, communicate the recommendations to the Secretary-General of the United Nations, who will in turn communicate the advice to the Commission on Narcotic Drugs (CND). The report summarizes the review of 16 substances and the ECDD recommendations for the scheduling of 12 substances. The report also contains updates from international bodies concerned with controlled substances, as well as summaries of the follow-up on the recommendations made at the previous Committee meeting. Issues identified for consideration at future Expert Committee meetings are also covered.