Understanding Clinical Trials

Phase 1 asks whether a compound is tolerated and how the body handles it, usually in a small number of participants. Phase 2 looks for a signal of effect and refines dosing. Phase 3 tests that effect against placebo or an active comparator in a large population.

Registration on a public trial registry before enrolment is what makes results appraisable later: it fixes the primary endpoint in advance.

Primary and secondary endpoints

A trial is designed and powered around its primary endpoint. Secondary endpoints are informative but not conclusive — which is why a trial that misses its primary endpoint and reports a positive secondary one is a mixed result, not a success.