The acceptability of nonmedical use for a particular drug is a function of diverse social needs. Drug dependence is due less to intrinsic effects than to the situation in which drug taking occurs. An addictive level of drug self-administration is a symptom of behavioral troubles rather than a definition of the trouble itself. The intrinsic effects of drugs do not in themselves produce either misuse or evoke specific kinds of behavior such as sexual or aggressive activities. Drugs can, however, come to function as discriminative stimuli for socially sanctioned behavior that would not under other circumstances be tolerated. The intrinsic reinforcing potential of an agent evolves in and dominates situations in which other reinforcing opportunities are either absent or remain unavailable to an individual who is unprepared to exploit them. While certain intrinsic properties of a drug contribute to its potential as a reinforcer (e.g., rapid onset and brief duration of action), reinforcing efficacy is notoriously malleable. It is a function of historic and currently-acting factors, particularly social reinforcers. The importance of physical dependence in the maintenance of drug seeking and taking is mainly unproven and probably overrated. Situations under which important reinforcers are available only in small portions intermittently can induce various excessive activities, including an untoward concern with obtaining and using drugs. Drug dependence prevention as a species of environmental dependence can be best effected by either alterations in the intermittent reinforcement situations inducing excessive behavior or by providing opportunities and training with respect to reinforcing alternatives other than drugs.