This publication represents a portion of the ongoing work of the Pan American Health Organization with regard to study of the epidemiology and health effects of drug abuse. The rapid spread and pervasiveness of the use and abuse of alcohol, tobacco, and illegal drugs has created a grave situation which has caught the countries of the Region of the Americas unprepared and which far exceeds the capacity of the governments to respond effectively. Thus, it is essential to strengthen knowledge in this field and to promote epidemiologic studies such as those reported here. Health authorities, researchers, and health workers involved in drug abuse prevention and treatment will find the material in this volume useful for understanding the current status of the drug abuse problem and what is being done to combat it.