This report presents the recommendations of the thirty-eighth 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. The report summarizes the review of twelve substances and the ECDD recommendations for the scheduling of ten substances. Furthermore, the ECDD discussion and recommendation for pre-reviews of pre-reviews of cannabis and its component substances are included in this report. 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, and on the discussions of prioritization of substances, surveillance systems of new psychoactive substances and terminology. Issues identified for consideration at future Expert Committee meetings are also listed.