In health care, a clinical trial is a comparison test of a medication or other medical treatment (such as a medical device), versus a placebo (inactive look-a-like), other medications or devices, or the standard medical treatment for a patient's condition. Clinical trials vary greatly in size: from a single researcher in one hospital or clinic to an international multicenter study with several hundred participating researchers on several continents. The number of patients tested can range from as few as 30 to several thousands. While undergoing the trial, the agent being tested is called an investigational new drug.