The investigational medication or vaccine is evaluated in a small group of people for the first time to gather information on its safety, dosing, and side effects.

The investigational medication or vaccine is evaluated in a larger group of patients to see if it is effective and to better understand its safety.

The investigational medication or vaccine is given to a large group of patients to evaluate its effectiveness, compare it to commonly used medications (known as standard of care) or placebo, and collect information regarding the safety of the investigational medication.

Phase IV trials are conducted after a medication or vaccine has been approved by a country’s regulatory medical authorities. The purpose of these trials is to gather more information on the medication or vaccine’s effects and side effects.