One of the questions that scientists must ask as they develop new drugs to treat various diseases is whether or not the new prescription drug is likely to be abused or used for the wrong reasons because of the effect it has on users. The likelihood that a drug will be abused by a patient must be carefully weighed against the benefit provided by the drug. Researchers must identify any and all reinforcing effects a drug may have that could lead to future abuse. In the past, researchers made predictions about the likelihood of abuse by observing humans who used the drugs, and sometimes by conducting experiments with these users. Increasingly, experiments with animals are replacing this method.

Research conducted since the early 1960s has shown that animals such as monkeys and rats will...