Term
Clinical trial phases
The staged sequence of human testing: phase 1 (safety and dose), phase 2 (proof of concept), phase 3 (confirmation), phase 4 (post-marketing).
Phase 1 gives a drug to humans for the first time, usually small groups, to establish safety and dosing. Phase 2 tests whether the drug works at all in patients, often across doses; a larger dose-ranging study is sometimes labelled 2b. Phase 3 is the confirmatory test regulators rely on: large, randomized, designed to support approval. Combined labels like 1/2 and 2/3 mark seamless designs that roll one phase into the next.
Phase 4 happens after approval: surveillance, label extensions, real-world questions. Because it is post-marketing by definition, a phase 4 study is not evidence of pre-approval progress, which is why this site's stage derivation ignores it when computing how far a drug has advanced.
On this site: Browse drugs by stage ↗
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