A part of the clinical research process that answers specific questions about whether treatments or other interventions that are being studied are safe and work. Phase I trials test the best way to give a new treatment and the best dose. Phase II trials test whether a new treatment has an effect on the disease. Phase III trials compare the results of people taking a new treatment with the results of people taking the standard treatment. Phase IV trials are done using many people after a treatment has been approved and marketed to check for side effects that weren’t seen in the Phase III trial.
Source: NCI
