DOUBLE-BLIND TRIAL

a clinical trial involving volunteers who take an experimental drug or a control substance. The control substance is usually a drug already approved for use in the disease, but sometimes it's a placebo. In a double-blind trial, a lab prepares the experimental and control substances and labels them so that neither the researchers nor patients know which individuals are getting the experimental drug. Only after the trial is finished do the researchers and patients learn which patients were taking the experimental drug. In HIV-related trials, the placebo is commonly replaced with some approved anti-HIV treatment. (also see clinical trial, and open label trial.)