A wide range of theories have at various times been advanced to account for the use and misuse of alcohol, tobacco, illegal drugs, and prescribed drugs. Several general reviews have been produced in recent years (Fazey 1977, Plant 1981, Peck 1982). These have concluded that drug use and misuse are caused by many factors that act both singly and in combination. The main implication of the complex etiology of drug use and misuse is that no single theory can explain them and no single policy is likely to control use or prevent misuse. The effects of any drug depend on an interaction between the substance used, the characteristics of the user, and the environment in which use occurs. The main factors that have been highlighted as contributing to drug use and to drug-related problems may be subdivided into constitutional (biological), individual, and environmental. Constitutional theories are concerned with either biological predispositions or with the relationship between the drug and the body. Individual theories are largely concerned with either unusual personality traits or more general factors, such as introversion and extroversion. Environmental factors include social, cultural, economic, political, and historical influences. Innumerable general factors have been suggested as contributing to drug use and misuse, including alienation or "anomie," unemployment, affluence, and the availability or scarcity of alternative substances or gratifications. Some etiological factors are either intractable or are very difficult to counter. These include constitutional predispositions and individual traits. It may not be possible to change people's biological and psychological make-up. Even so, it is worth identifying subgroups that are, in some respects, "at risk" for reasons of their ethnicity, age, sex, physiology, or background. Other etiological factors are more worthwhile targets for attack by social policy. These are all environmental, including the availability of drugs, ideologies, and peer pressure to use drugs. 41 references