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| CTRP Phase Value | ClinicalTrials.gov Value | Definition |
|---|---|---|
| Early Phase I | Early Phase 1 (Formerly listed as "Phase 0") | Exploratory trials, involving very limited human exposure, with no therapeutic or diagnostic intent (e.g., screening studies, microdose studies). See FDA guidance on exploratory IND studies for more information. |
| I | Phase 1 | Includes initial studies to determine the metabolism and pharmacologic actions of drugs in humans, the side effects associated with increasing doses, and to gain early evidence of effectiveness; may include healthy participants and/or patients. |
| I/II | Phase 1/Phase 2 | Trials that are a combination of phases 1 and 2. |
| II | Phase 2 | Includes controlled clinical studies conducted to evaluate the effectiveness of the drug for a particular indication or indications in participants with the disease or condition under study and to determine the common short-term side effects and risks. |
| II/III | Phase 2/Phase 3 | Trials that are a combination of phases 2 and 3. |
| III | Phase 3 | Includes trials conducted after preliminary evidence suggesting effectiveness of the drug has been obtained, and are intended to gather additional information to evaluate the overall benefit-risk relationship of the drug. |
| IV | Phase 4 | Studies of FDA-approved drugs to delineate additional information including the drug's risks, benefits, and optimal use. |
| NA (Not applicable) | N/A | Trials without phases (for example, studies of devices or behavioral interventions). |
