Drug Testing in Humans: Studying Potential for Abuse

Nearly any drug used to treat illness also poses certain risks. One such risk, generally limited to drugs that act on the central nervous system, is that the drug will be abused because of those effects. Such a drug is said to have "abuse potential" or "abuse liability." If it has important medicinal uses, it may still be available by prescription, but legal controls will be placed on how it can be prescribed. New drugs are tested to determine their potential for abuse so that both the public and the medical profession can be warned about the need for appropriate caution when using them.

Conducting tests on humans serves several purposes in the development of safer and more effective drugs. When research done on laboratory animals shows that a drug might have abuse potential, these findings must be confirmed with tests on humans. Humans who participate in testing describe what kinds of things they notice when they take a particular drug. Testing drugs on humans can also help determine appropriate dose levels and dosage forms to ensure safety and efficacy while minimizing unwanted side effects. Finally, testing in humans helps reduce the availability of abusable drugs to those who are likely to abuse them.

In most studies, the human volunteer subjects are experienced to some degree as drug users. Some studies involve people with histories of intensive drug use and abuse over extended periods. These people make good test subjects because they are similar to those most likely to abuse drugs. Other studies use students or volunteers whose misuse and abuse of drugs or alcohol has been mostly recreational . Tests in these people can determine whether certain widely available medications, such as sleeping pills or appetite suppressants, are likely to be abused. Participants are often selected on the basis of some special features (such as anxiety levels or level of alcohol consumption) in order to determine the extent to which such factors influence the outcome of the tests.

The use of questionnaires has improved researchers' ability to measure the subjective effects of drugs. Volunteers who are experienced drug users answer questions after they have taken a drug. For instance, they may be asked to describe how they feel and what they liked and disliked about the drug's effects. Testing can also indicate whether a person is likely to keep taking a drug with abuse potential. Laboratory studies with volunteers who are experienced drug users, for example, have shown that they will perform bicycle- riding exercises to obtain doses of abused drugs, which they self- administer. These exercise studies are set up so that the volunteer can give herself or himself a higher dose of the drug being tested, if they first exercise for a certain amount of time. When a drug of abuse is tested, volunteers will choose to exercise for longer periods to obtain higher doses. However, when a placebo or a drug that is not abused is made available as a reward for bicycle riding, the subject does not choose to take it, and will not increase exercise time in order to get it.

Predicting a drug's abuse liability is complicated because drugs of abuse are often used in combination. Thus a large number of possible drug combinations need to be tested. Yet few testing procedures have been developed for assessing the interactions of substances, such as marijuana and alcohol, that abusers often use simultaneously.

Scientists and the public set standards and regulations for conducting research and testing in human volunteers. The volunteer must understand the risks and benefits of the testing procedure and sign a consent document in the presence of a witness who is not associated with the research.

see also Drug Testing in Animals: Studying Potential for Abuse; Drug Testing Methods and Analysis.