Clinical trials are conducted in a series of different phases each designed to answer a separate research question.
Phase I: Researchers test a new drug or treatment in a small group of patients to evaluate its safety, determine a safe dosage range, and identify side effects. Phase I trials aim to find the best dose of a new drug with the fewest side effects.
Phase II: The drug or treatment is given to a large group of patients to see if it is effective and to further assess its safety. Patients are closely watched to see if the drug works. If a drug is found to work, it can be tested in a phase III clinical trial.
Phase III: The drug or treatment is given to larger groups of patients to confirm its efficacy, monitor side effects, compare it to commonly used treatments, and collect information that will allow the drug or treatment to be used safely. Phase III trials compare a new drug to the standard-of-care drug. These trials assess the side effects of each drug and which drug works better. Phase III clinical trials are often needed before the FDA will approve the use of a new drug for the general public.
Phase IV: Studies are done after new drugs are approved by the FDA or treatments have been marketed to gather information on it’s effectiveness in various populations. The drug is tested in several hundreds or thousands of patients. This allows for better research on short-lived and long-lasting side effects and safety. Physicians can also learn more about how well the drug works and if it’s helpful when used with other treatments.