Phase of investigation, usually applied to a drug trial.
Phase 1: the first tests of a treatment in humans that aim to test safety and the best drug dose.
Phase 2: aim to see how well the new treatment works and to monitor for side effects.
Phase 3: aim to test if the new treatment (the intervention treatment) is better than the current best standard treatment.
Phase 4: aim to assess any long-term side effects of a new treatment and occur after a drug has been licensed for use and put on the market.
Note that not all ANZCTR trials complete this field as it is not compulsory.