FDA Terminology

This page discusses several different common terms and phrases used by the FDA and the drug approval process. It will cover all phases of FDA drug approval, what specific designations mean, and special clauses provided by the FDA.


Following drug discovery and genesis of a new compound or use, a company may choose to enter a compound into the pre-clinical phase through the FDA.  This phase tests the compound in question in non-human subjects, typically primates, rodents, or dogs. The pre-clinical phase tests the drug on non-human subjects to gather efficacy, toxicity, and utilizes the data to determine pharmacokinetic and pharmacodymanics in subjects.  Doses in this phase are typical variant as scientists use the subjects to gather tolerance levels that can be translated to humans.  This phase is also developed within a laboratory through researchers, not in a clinical setting.  

Investigational New Drug Application (IND)

An IND is filed by a company, group of researchers, or organization developing a drug to present a potential drug candidate to the FDA displaying the results of the pre-clinical studies.  The data must show testing on laboratory animals and propose plans for human testing.  The FDA will determine if the drug will be considered safe for use to move forward in human trials or if there is a pressing need to fulfill an unmet need in the market immediately.   Filing an IND is the first large milestone that a company takes towards marketing a potential drug candidate.  

Phase 1

The Phase I studies are conducted on a set of healthy volunteers which involves varying doses of the compound throughout the volunteers.  The primary focus of Phase I studies is to determine what the drug's most frequent side effects are and how the drug is metabolized and excreted.  Doses are typically done sub-therapeutic with ascending doses to gauge side effects with dose levels.  Patient sizes range from 20-100 healthy individuals (in the case of Cancer Drugs - Cancer Patients), and determines whether the drug is safe to continue trials to test for efficacy at higher therapeutic dosages.  Results from Phase I are early on in development, and should be taken with a grain of salt. 

Overall likelihood of approval (LOA) for Phase I for all developmental candidates is around 10%, and up to 12% for all indications outside of Oncology.  Chronic Diseases with high populations had lower LOA from Phase I vs. overall datasets from other diseases and conditions. Hematology has show the highest LOA from Phase I with around 25% and Oncology the lowest at 5%.

Phase II

In Phase 2 studies, researchers administer the drug to a group of patients with the disease or condition for which the drug is being developed. Typically involving a few hundred patients, these studies aren't large enough to show whether the drug will be beneficial to the overall populace.  

Instead, Phase 2 studies provide researchers with additional safety data. Researchers use these data to refine research questions, develop research methods, and design new Phase 3 research protocols.  Researchers seek to asses the efficacy and side effects at therpeutic doses, up to this point the drug is not presumed to have any therpeutic effect whatsoever.

Phase III