Phase 0: Exploratory IND studies in limited human subjects
Phase 1: Early stage of testing
Phase 2: Preliminary safety and efficacy
studies
Phase 2a: Pilot trials in selected populations
Phase 2b: Pivotal trials; most rigorous test of safety
Phase 3: Expanded large-scale studies
Phase 3b: Trials started after NDA submission but before marketing approval is received
Phase 4: Postmarketing studies