Clinical trials are phase I, phase II, or phase III. Before a treatment gets into a clinical trial it goes through preclinical testing. During this phase, researchers test the drug on cells or animals to determine if it’s safe enough to go into human trials. In a phase I trial, the researchers are trying to figure out the safest dose of treatment. They also look at what side effects the treatment may cause. A small number of people participate in phase I trials. Phase II trials enroll more people. These studies look at how a treatment affects the body and try to better understand how the treatment works. Phase III trials enroll much more people, often hundreds or even thousands. Phase III trials compare the new treatment to the existing treatment. This helps researchers evaluate if the new treatment offers improvement over the existing treatment.