In medicine, a randomized, controlled trial (RCT) is a form of research designed to provide information regarding the potential benefits and risks of a treatment in individuals (Figure).1 Treatments typically are new drugs or medical devices, but could also include new diagnostic tests or therapeutic strategies (ie, an approach to treating a patient). RCTs are invaluable to the medical community to help improve the care of patients. Figure. Basic structure of a classic randomized, controlled trial (RCT). For the sake of simplicity, only one experimental arm is shown, but RCTs can have multiple experimental arms. The control arm may consist of an active therapy (active-controlled) or a placebo (an inactive substance; placebo-controlled). Ideally, a double-blind design is used in which neither the investigator nor the subject know the arm to which the subject has been allocated. RCTs come in many shapes and sizes, from enrolling a few patients at 1 hospital to enrolling tens of thousands of patients at hundreds of hospitals or clinics across the world. Given the size and complexity of such RCTs, they are typically designed by a panel of experts (eg, physicians experienced in treating a certain disease) and sponsored by a governmental agency (eg, the National Institutes of Health) or a pharmaceutical or biotechnology company. A scientific protocol serves as an operating manual for how the trial is to be conducted, ensuring consistency across all sites. Common elements of the trial protocol that a study team is likely to discuss with a potential research subject are listed in the Table.2 Key …