Any experiment in which a drug is administered or dispensed to one or more human subjects. Relating to investigational drugs, an experiment is any use of a drug (except for the use of a marketed drug) in the course of medical practice. While there are many other definitions, this is the Food and Drug Administration's definition and would seem the most appropriate one to use given the nature of this topic. Please note that the Food and Drug Administration does not regulate the practice of medicine and prescribers are (as far as the agency is concerned) free to use any marketed drug for "off-label use. "