| Code | Display | Definition |
| n-a | N/A | Trials without phases (for example, studies of devices or behavioral interventions). |
| early-phase-1 | Early Phase 1 | Designation for optional exploratory trials conducted in accordance with the United States Food and Drug Administration's (FDA) 2006 Guidance on Exploratory Investigational New Drug (IND) Studies. Formerly called Phase 0. |
| phase-1 | 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. |
| phase-1-phase-2 | Phase 1/Phase 2 | Trials that are a combination of phases 1 and 2. |
| phase-2 | 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. |
| phase-2-phase-3 | Phase 2/Phase 3 | Trials that are a combination of phases 2 and 3. |
| phase-3 | 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. |
| phase-4 | Phase 4 | Studies of FDA-approved drugs to delineate additional information including the drug's risks, benefits, and optimal use. |