The author conducts a detailed terminological study on the notions used in the domain of the circulation of narcotic and psychotropic substances, and their analogues and precursors. The correct understanding of the meaning and content of the law by its beneficiaries and addressees contributes to the achievement of the fundamental principle of a state, which is the supremacy of the law in all social life fields. The author analyzes the reasons of the inadequate use of the notions from the discussed domain by the law addressees. The importance of the terminological perfecting is underlined. The definitions of notions, stipulated in the national and other countries’ legislature and given by different researchers are analyzed and compared. Throughout the article, the author gives suggestions for improving the terminological side of the domain of circulation of narcotic and psychotropic substances, and their analogues and precursors.