Clinical Trial Phases Explained: I to IV

Phase 1 tests safety in small groups of healthy volunteers or patients. Phase 2 explores dosing and early efficacy in dozens to hundreds.

Phase 3 confirms efficacy in hundreds to thousands against standard treatment, powering drug approvals. Phase 4 studies real world use after approval.

Each phase answers a different question, and most drugs fail somewhere along this pipeline, only about 10 percent of drugs entering trials reach patients..