Unblinding is the process in which the allocation code is broken and one or more parties to the trial are made aware of which treatment a participant is receiving.

Unblinding may be done intentionally and may be planned or due to an emergency. Planned unblinding can be performed as a part of the protocol to allow participants to know what treatment they were receiving so that they may plan their subsequent care. Unblinding can also be performed in response to an emergent situation such as a severe adverse affect or potential overdose. The Principal Investigator must report emergency unblinding to the sponsor and IRB. Documentation for unblinding procedures must be included in the standard operating procedure as a part of regulatory requirements.

Unintentional or accidental unblinding can occur when treatment allocation is revealed to the research staff or participants outside of the standard process. The accidental unblinding must be reported to the sponsor and IRB by the Princial Investigator as soon as possible.

Source: Food and Drug Administration (FDA). (2020, May). E6(R2) Good Clinical Practice: Integrated Addendum to ICH E6(R1). US Department of Health & Human Services. https://www.hhs.gov/guidance/document/e6r2-good-clinical-practice-integrated-addendum-ich-e6r1