“…On conceptual grounds, it can be argued that the transition from drug use to drug dependence in the population is determined partly by the re-inforcing functions served by drug-taking and associated behaviors, with a linkage back to profiles of drug activity discovered through laboratory research (e.g., see Schuster, 1989;Thompson, 1981). In addition, this transition seems to be determined in part by other factors, some linked to the reinforcing functions of drug use, and some not so readily studied inside the laboratory (e.g., see Brady, 1989;Glantz & Pickens, 1992;Schuster, 1989). In theory, the array of these interrelated factors includes relative drug availability and opportunities for use of different drugs as well as their cost; patterns and frequencies of drug use that differ across drugs; different profiles of vulnerabilities of individuals whose extramedical use starts with one drug versus another, as well as both formal and informal social controls and sanctions against drug use or in its favor, which might be exercised either within intimate social fields such as the family or workplace or by larger units of social organization.…”