Clinical trials are research investigations which help to determine if a new intervention works, if it is safe, and if it is better than the interventions that are already available. It’s only through clinical trials that new medicines, treatments and devices can be registered for public use.
A clinical trial is a research study designed to learn how our bodies respond to medicines or other treatments. Clinical trials:
Clinical trials are sometimes called clinical studies and clinical research.
Tests the medicine or vaccine in a small group of 20 to 100 volunteers who are usually healthy, but not always.
The trial often takes place in a hospital.
The goals of Phase 1 trials are to:
Phase 1 trials can take six months to one year to complete.
Tests the medicine or vaccine in approximately 100 to 500 volunteers.
In the case of medicines, volunteers usually have the disease or condition the investigational medicine is designed to treat. In vaccine studies, the volunteers are usually healthy.
The goals of Phase 2 trials are to:
Phase 2 trials can take from six months to one year to complete
Tests the medicine or vaccine in large groups of trial participants (from several hundred to several thousand).
For medicines, volunteers have the disease or condition the medicine is designed to treat. In vaccine studies, the volunteers may be healthy or have diseases or conditions. Phase 3 trials take place in hospitals, clinics or doctors' offices.
Researchers closely monitor participants at regular intervals to:
Phase 3 trials can take one to four years to complete, depending on the disease, length of study, and number of volunteers.
Thousands of people usually participate in ongoing trials.
Phase 4 clinical trials are conducted after the medicine or vaccine has been registered by the appropriate government and regulatory agencies and is being marketed.
Researchers continue to gather information about:
Phase 4 trials are ongoing.
Age, race, gender, ethnicity, and many other factors play into how a person will react to an investigational medication treatment. How well a medication works, its chance of causing side effects, and the type of side effects can differ by ethnic group. Including diverse participants in clinical trials helps researchers understand how the results will apply to the broader population. To read more about MSD’s commitment to diversity in clinical trials, visit our Diversity section.
Taking part in a clinical trial is a process. We’ve outlined the steps you can expect before, during, and after being in a clinical trial.
Before you decide if you’ll join a clinical trial, learn as much as possible about it. You should feel comfortable asking the researchers all your questions about the trial, the care you can expect, and if there are costs. Explore our list of questions to ask the research team.
Understanding clinical trials is important when making the decision to join one. Our FAQ section has answers to commonly asked questions and a glossary of words to know.
