Evidence-appraisal glossary
Open-label trial
A trial in which both participants and investigators know which treatment each person is receiving; there is no blinding. Randomization may still be used to assign treatment.
Also called: unblinded trial, open trial.
Open-label designs are sometimes unavoidable, for example when comparing surgery with a drug or when a placebo is impractical. Knowing the assignment does not undo random allocation, so it can still support causal comparison. The weakness is bias that enters after assignment: unblinded patients and clinicians can differ in expectations, co-treatment, and how they report or assess outcomes, which matters most for subjective endpoints like pain or symptom scores and less for hard outcomes like death.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.