MSD
Clinical Trials
Clinical trials may help researchers find better treatments. It’s only through clinical trials that new medicines, treatments, and devices can be approved 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.
Investigational medication is tested for safety on a relatively small group of 20 to 100 volunteers who are usually healthy, but not always.
The trial may happen in a doctor’s office or a hospital.
The goals of Phase 1 trials are to determine:
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 determine:
Phase 2 trials can take from six months to one year to complete
Tests the medicine or vaccine in approximately 1,000 to 5,000 volunteers.
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 may happen in a doctor's office, a clinic, or a hospital.
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 approved 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. To find out if a treatment is safe and works well for all people, researchers must have diverse participants in clinical trials. 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.
Our FAQ section has answers to commonly asked questions and a glossary of words to know.
