| CTRP Phase Value | Definition |
|---|---|
| Early Phase I | 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 | 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 | Trials that are a combination of phases 1 and 2. |
| II | 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 | Trials that are a combination of phases 2 and 3. |
| III | 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 | Studies of FDA-approved drugs to delineate additional information including the drug's risks, benefits, and optimal use. |
| NA (Not applicable) | Trials without phases (for example, studies of devices or behavioral interventions). |
 |
