An open-label study is a clinical trial in which no blinding occurs. This means that both the study participants and the investigators and study team know which treatment each participant is receiving. This study type contrasts with single-blind or double-blind studies, in which this information remains concealed.
Open-label studies are frequently used in early phases of clinical development (Phase I) to investigate dose-finding and safety, or as long-term extension studies following a blinded main study. They are simpler and more cost-effective to conduct, but carry a higher risk of systematic errors (bias), as knowledge of the treatment can influence the expectations and behavior of patients and physicians. Therefore, results from open-label studies are often considered less conclusive for efficacy than those from blinded, randomized, controlled trials.