Clinical Trials Phases

Early Phase 1 (Formerly listed as "Phase 0"): Exploratory study involving very limited human exposure to the drug, with no therapeutic or diagnostic goals (for example, screening studies, microdose studies)

Phase 1: Studies that are usually conducted with healthy volunteers and that emphasize safety. The goal is to find out what the drug's most frequent and serious adverse events are and, often, how the drug is metabolized and excreted.  In most cases, 20 to 80 healthy volunteers or people with the disease/condition participate in Phase 1 and the study length lasts for several months.

Phase 1/Phase 2: Trials that are a combination of phases 1 and 2.

Phase 2: Phase 2 studies begin if Phase 1 studies do not reveal unacceptable toxicity. While the emphasis in Phase 1 is on safety, the emphasis in Phase 2 is on effectiveness. Studies that gather preliminary data on effectiveness (whether the drug works in people who have a certain disease or condition). For example, participants receiving the drug may be compared with similar participants receiving a different treatment, usually an inactive substance (called a placebo) or a different drug. Safety continues to be evaluated, and short-term adverse events are studied. Typically, the number of subjects in Phase 2 studies ranges from a few dozen to about 300 with a study length of several months to 2 years.

Phase 2/Phase 3: Trials that are a combination of phases 2 and 3.

Phase 3: Phase 3 studies begin if evidence of effectiveness is shown in Phase 2.Studies that gather more information about safety and effectiveness by studying different populations and different dosages and by using the drug in combination with other drugs. The number of subjects usually ranges from several hundred to about 3,000 people. Length of study can be from 1 to 4 years.

Phase 4: Phase 4 trials are carried out once the drug or device has been approved by FDA during the Post-Market Safety Monitoring i.e., studies occurring after FDA has approved a drug for marketing. These including postmarket requirement and commitment studies that are required of or agreed to by the sponsor. These studies gather additional information about a drug's safety, efficacy, or optimal use. The number of subjects in Phase 4 ranges from several thousand volunteers who have the disease/condition.


Clinical trials for medical devices

The Food and Drug Administration (FDA) has established classifications for approximately 1,700 different generic types of devices and grouped them into 16 medical specialties referred to as panels. Each of these generic types of devices is assigned to one of three regulatory classes based on the level of control necessary to assure the safety and effectiveness of the device. More information about the three classes and the requirements which apply to them can be found using the resources below:




Page last updated 8:50 AM, June 29, 2022