Definition: A type of clinical trial in which neither the researchers nor the participants knows which drugs are being taken.
Participants are randomized to one of two or more study groups, or "arms," and all medications and procedures that are given are designed to look identical. Therefore, even if the study involves comparison of a new drug to a placebo or an existing therapy, all medications given to study participants will look exactly like each other and be taken exactly the same way. The treatments can only be identified by study numbers that are usually locked away off-site. This is done to eliminate any bias that might be introduced if research staff knew which participant was receiving which drug or placebo.
Double-blinded trials are considered the most objective type of study and are known as the "gold standard" of drug trials.
