clinical trial phase https://www.clinicaltrials.gov/ct2/help/glossary/phase clinical trial stage The quality of a clinical trial that studies a drug or biological product. The phase is based on the study's objective, the number of participants, and other characteristics. According to USA FDA, there are five phases: Early Phase 1 (formerly listed as Phase 0), Phase 1, Phase 2, Phase 3, and Phase 4. Leon Li, Asiyah Lin, Oliver He https://www.who.int/ictrp/network/trds/en/ phase process quality