All clinical trials have eligibility requirements based on the clinical trial protocol. This includes rules about who can be in the trial and the details of the treatment procedures and medications. The clinical trial protocol is designed to ensure the trial protects the health of the trial participants. For the best outcome, researchers want participants who are similar so that reviewing the results is simpler. For example, a study may want people of a certain age range or at a particular disease stage. During the screening process, the researchers will ensure you meet the eligibility criteria for the trial.