An experimental drug is a substance that has been tested in a laboratory and has got approval from regulatory authorities to be tested on people. In the United States, the body responsible for approval is the U.S. Food and Drug Administration (FDA). A drug may be approved for use in one disease or condition but be considered experimental or investigational in other diseases or conditions.
An example of a medical drug that has been tested but not yet on the market is medical cannabis.
This article incorporates public domain material from the U.S. National Cancer Institute document "Dictionary of Cancer Terms".