In the Phase III, the drug or treatment is given to large groups of people to confirm its effectiveness, monitor side effects, compare it to commonly used treatments, and collect information that will allow the drug or treatment to be used safely.

In the Phase IV, the researchers test a new drug or treatment in a small group of people for the first time to evaluate its safety, determine a safe dosage range, and identify side effects.

Clinical trials are conducted in a series of steps, called phases – each phase is designed to answer the same research question.

In the Phase I, the studies are done after the drug or treatment has been marketed to gather information on the drug’s effect in various populations and on any side effects associated with long-term use.