A drug available only for experimental purposes because its safety and effectiveness have not yet been proven.
A new drug that is undergoing clinical trials to prove its effectiveness and safety (see clinical trials).
(in-VES-tih-GAY-shuh-nul drug) A substance that has been tested in a laboratory and has gotten approval from the U.S. Food and Drug Administration (FDA) to be tested in people. A drug may be approved by the FDA for use in one disease or condition but be considered investigational in other diseases or conditions. Also called an experimental drug.