ABSTRACT
Although the effects of psychoactive drugs can be studied at many different levels, ultimately any analysis must address issues of a behavioural nature. Experiments involving isolated neurons or receptor activity, for example, take on added significance when related to the intact behaving organism. On a different level, psychiatric disorders are most clearly manifested and described as disturbances in behaviour. Drugs with potential therapeutic efficacy in psychiatry are clinically evaluated by their ability to alter the dominant behavioural symptoms of a particular disease. The excessive use of abused drugs is also characterized by marked changes in drug-taking and druginduced behaviour. The conspicuousness and importance of behaviour under such conditions should not be interpreted as only indicating that it is merely a passive transmitter of changes or influences occurring at a different level. Often, as we shall see, behaviour itself and the variables that control it can play a prominent and active role in directly determining drug action.
