Once a substance has completed preclinical testing, the manufacturer files an Investigational New Drug (IND) Application with the U.S. Food and Drug Administration (FDA). The IND becomes effective if the FDA does not disapprove of it within thirty days. The IND allows scientists investigating the drug to distribute it to responsible investigators for use in clinical trials that will involve humans. All clinical trials must be reviewed and approved by the Institutional Review Board (IRB) of the medical institution that will be conducting the clinical trial.
Normal, healthy volunteers are used in Phase I clinical trials. Phase I studies are several months in duration, and the size of the group can range from twenty to eighty subjects. The purpose of these trials is to determine the safety profile or benefit to risk assessment for use in humans, including the safe dosage range; and absorption, distribution, metabolism, and excretion in humans.