There are different types of clinical trials.

Natural history studies provide valuable information about how disease and health progress

Prevention trials look for better ways to prevent a disease in people who have never had the disease or to prevent the disease from returning. Better approaches may include medicines, vaccines, or lifestyle changes, among other things.

Screening trials test the best way to detect certain diseases or health conditions

Diagnostic trials determine better tests or procedures for diagnosing a particular disease or condition

Treatment trials test new treatments, new combinations of drugs, or new approaches to surgery or radiation therapy.

Quality of life trials (or supportive care trials) explore and measure ways to improve the comfort and quality of life of people with a chronic illness.