The Four Phases of Clinical Trials
Phase I clinical trials: Is the treatment safe?
Phase I trials usually include a small number of people. This number varies from one trial to the next, but there are usually fewer than 100 participants in a Phase I trial. The participants may be people with a specific disease or condition or healthy volunteers.
Researchers conduct Phase I trials to learn more about how a treatment behaves in the human body, to learn about any side effects that might happen when someone takes a treatment, or to find the right dose of a treatment to use in Phase II. In some Phase I trials, such as cancer trials, researchers will also look at how each participant’s disease responds to treatment.
Phase II clinical trials: Does the treatment work?
Phase II trials usually include more participants, up to several hundred people. While researchers continue to study a treatment’s safety in Phase II trials, they also begin to collect data about if and how well a treatment works in people who have the disease or condition that it is being developed to treat.
Phase III clinical trials: Is it better than what’s already available?
Phase III trials usually include large numbers of participants. Some Phase III trials are conducted in multiple countries and may include thousands of people. Phase III trials are used to collect more information about how safe a drug is and how well it works.
Phase III trials will often compare an experimental treatment with the current standard of care to see if it works as well or better, or has fewer side effects, than what is already available to patients. To do this, researchers will assign participants to different treatment groups – participants in one treatment group will receive the new treatment, while participants in another group will receive standard-of-care therapy. Alternatively, participants in one group might receive the new drug plus standard therapy, while participants in another treatment group might receive standard therapy alone.
Phase IV clinical trials: What else do we need to know?
Phase IV trials may be conducted after a drug or device has been approved for use. Phase IV trials are done to study how safe a drug is and how well it works in large, diverse populations over long periods of time. Phase IV trials might identify side effects that were not seen in smaller, shorter trials.