Why are trials divided into phases?
Trials in each phase are designed to reveal certain information. Patients may be eligible for studies in different phases depending on their general condition and type of disease. More patients take part in the later-phase studies than in earlier ones. In a Phase I study, a new treatment is given to relatively few people (20 to 100 healthy volunteers, typically). The researchers must find the best way to give a new treatment and how much of it can be given safely. They watch carefully for any harmful side effects. The treatment has been tested in laboratory and animal studies, but no one knows how people will react. Phase I studies may involve significant risks for this reason. Phase II studies determine the treatment’s effects on the disease or disorder. This phase of testing usually involves a few hundred patients, mostly those who have the disease or disorder of interest. These are usually randomized, controlled studies, so that the treatment’s safety and effectiveness (efficacy) ca
