Clinical trials have several procedures to protect the safety of the people who join the study.
Several groups have to approve the protocol for every study. Every study center has an IRB, which includes doctors, other health care providers, consumers, and sometimes members of the clergy who do not have any personal interest in the results of the study which would bias them. They serve as neutral reviewers and ensure that the study is managed fairly and that no one is likely to be harmed who may decide to join. Each Phase III cancer prevention study also has a special group called a Data Safety and Monitoring Committee that looks at the test results and monitors the safety of the participants, and decides whether the study should go forward as originally planned.