Table 1.

Clinical trial phases as regulated by the FDA. Table detailing FDA-regulated clinical trial phases as a function of their length, purpose, and test population. ^∗IND is not a distinct phase of the clinical trial process but is a required application between the preclinical phase and phases I-IV.

	Length of phase (years)	Purpose	Test population
Preclinical	6.5	Toxicity studies	Nonhuman animals
IND∗	N/A	Successful completion of phase I Allows for clinical trial to be commenced	N/A
Phase 0	7 days	To show whether a drug's pharmacokinetics and pharmacodynamics warrant continued exploration	10-15 healthy volunteers
Phase I	1	Toxicity Pharmacokinetics	20-80 healthy volunteers
Phase II	2	Pharmacokinetics Efficacy Major side effects	100-300 patient volunteers
Phase III	3	Safety Efficacy	1,000-3,000 patient volunteers
FDA	1-2	Reviews NDA Validates data	N/A
Phase IV	N/A	Postmarketing surveillance trial	Public, entire population (prescribed treatment)