An open-label trial or open trial is a type of clinical trial in which both the researchers and participants know which treatment is being administered. This contrasts with single blind and double blind experimental designs, where participants are not aware of what treatment they are receiving (researchers are also unaware in a double blind trial).
Open-label trials may be appropriate for comparing two very similar treatments to determine which is most effective. An open-label trial may be unavoidable under some circumstances, such as comparing the effectiveness of a medication to intensive physical therapy sessions.
An open-label trial may still be randomized. Open-label trials may also be uncontrolled, with all participants receiving the same treatment.