Before revision: Phase 0 Phase 0 is a recent designation for optional exploratory trials conducted in accordance with the United States Food and Drug Administration's (FDA) 2006 Guidance on Exploratory Investigational New Drug (IND) Studies .
After revision: Phase 0 Phase 0 is a recent designation for optional exploratory trials , originally introduced by, but now generally adopted as standard practice the United States Food and Drug Administration's (FDA) 2006 Guidance on Exploratory Investigational New Drug (IND) Studies .