ABSTRACT
Animals readily learn to make responses (e.g. press a lever) to self-administer, through previously implanted catheters, many drugs misused by humans, and the drugs may thereby be defined as having positive reinforcing effects. The substances taken include opioid analgesics, psychomotor stimulants, nicotine, barbiturates, some benzodiazepines, alcohol and phencyclidine. With few exceptions, psychoactive drugs not associated with problems of abuse are not taken. Of the major classes of misused drugs, only cannabis and the LSD-type of hallucinogen have not been found to have reinforcing effects to date. The main characteristics of selfadministration behaviour have now been studied extensively with a wide range of compounds. Other studies have examined the control of drug-taking by aversive stimuli associated with withdrawal syndromes, and aversive effects of the drugs themselves; the latter may set upper limits to drug intake and may be important as regulating factors. Self-administration procedures and other techniques that measure related stimulus effects of drugs can therefore generate valid and reliable models for human drug misuse, and can be used to study the neurobiological basis of addiction. It is notable that additional highly addictive narcotic analgesics have not been marketed since self-administration became a standard procedure for evaluating abuse liability.
