Phase II study is conducted once a drug is proven to be safe. It must then be tested for efficacy. This second phase of testing may last from several months to two years, and involve up to several hundred patients. Most phase II studies are randomized trials. One group of patients will receive the experimental drug, while a second “control” group will receive a standard treatment or placebo. Often these studies are “blind”–neither the patients nor the researchers know who is getting the experimental drug. In this manner, the study can provide the pharmaceutical company and the FDA comparative information about the relative safety of the new drug, and its effectiveness. Only about one third of experimental drugs successfully complete both phase I and phase II studies.