The establishment of international control of opiates has been an important achievement of the international community. However, lack of implementation of a 1961 international convention and the inadequacies of the 1971 Convention on Psychotropic Substances have resulted in an inability to control the cannabis plant and the coca bush at the national and international levels. The provisions of the 1971 convention resulted from international compromise and are not designed in the best possible way to prevent the diversion of psychotropic substances from legal sources to illicit channels. For example, no appropriate provisions exist for the control and monitoring of international transactions. In addition, a discrepancy exists between the limited international control of certain substances and the larger scope of national control of hypnotics, sedatives, and tranquilizers. However, the 1971 convention provides a legal basis for bilateral and multilateral actions for detecting suspected diversion from licit to illicit markets and offers the possibility of improving prevention of such diversion. (Author abstract modified)