There are lots of different types of clinical trials, and they are not all drug trials.
Treatment trials test the how well and how safe a new treatment or a new way of using a standard treatment is. The treatment being tested might be, for example, a device, a drug, herbal supplement, complementary or alternative therapy, or a new tool, procedure or surgical technique.
Diagnostic trials study new tests and procedures that might help identify a disease earlier or better. Screening trials might be done to identify people with, or at risk of, a health condition before there are symptoms.
Prevention trials may look at ways to reduce the risk, or chance of developing a condition. Genetic studies are sometimes done as part of a clinical trial to help understand how genes may be linked to the detection or diagnosis of a condition, or the response to treatment.