Clinical trial: A scientific study that tests the effectiveness of a new medical treatment, drug or device in patients and volunteers. A clinical trial is a research study to determine whether a new drug, treatment, combination of drugs, medical device or procedure is safe and effective.Community trials address the efficacy of preventive interventions applied at the group level (e.g. , a social marketing campaign trial). Their are 4 stages of clinical trial although stages 1–3 are the most important. Access your Health Records. Manage your health care at any time, from anywhere, from your smart phone or computer. Clinical trials are research studies aimed at testing the effectiveness of new treatments, medications, vaccinations, and medical devices in people. A clinical trial is defined as the controlled, clinical testing in human subjects of investigational new drugs, devices, treatments or diagnostics. What is the difference between CRA and CRC roles in the field of clinical research?