What is it? Why is it important?

Emergency unblinding (EUB) is the act of revealing the blinded intervention of a participant during study conduct. This might become necessary in order to ensure participant safety including any required clinical management.

For EUB procedures:

  • Indicate emergency circumstances that necessitate an EUB
  • Define a system that allows for ongoing 24hr EUB (e.g. by phone, scratch cards, sealed envelope, IVRS)
  • Allow for rapid identification of participant treatment (e.g. intervention of placebo)
  • Allow for unblinding procedures in unexpected circumstances (e.g. electronic system with access to treatment allocation is out of order)
  • Describe how to document EUBs
  • Define how the Site-INV informs the SP-INV
  • Guarantee that blinding is maintained for all other study participants
  • Describe conditions where after EUB a participant can remain in the study (e.g. unblinding is not necessarily a reason for study drug discontinuation)


Circumstances that might necessitate an EUB can include:

  • Treatment of an AE
  • Occurrence of a SUSAR
  • A child has accidently ingested the IMP in a participant household
  • A request by the DSMB based on study-risk assessment

What do I need to do?

As a SP-INV of a blinded study:

  • Describe EUB procedures in the study protocol (e.g. circumstances, responsibilities). Define circumstances where unblinding is allowed (e.g. premature study termination, interim analysis, statistical analysis at study end)
  • Describe EUB procedures in an SOP or WI. These are important for training purposes and to ensure EUB compliance
  • Train Site-INV on EUB procedures, including how to document an EUB (e.g. EUN date, time, reason, result, name and role of the person requesting an EUB, name of the blind breaker) and how to notify the SP-INV
  • Submit EUB procedures to EC and RA (e.g. Swissmedic) for approval


As a Site-INV:

  • Once during study conduct, document and notify the SP-INV regarding any cases of premature unblinding (e.g. both accidental or cases performed as per procedure)

To maintain the overall quality and legitimacy of the study, EUB should only occur under exceptional circumstances.

Where can I get help?

Your local CTU can support you with experienced staff regarding this topic


ICH GCP E6(R2) – see in particular guideline

  • 4.7 Randomization procedures and unblinding


  • AE – Adverse Event
  • CTU – Clinical Trials Unit
  • DSMB – Data Safety Monitoring Board
  • EC – Ethics Committee
  • EUB – Emergency Unblinding
  • ICH GCP – International Council for Harmonisation - Good Clinical Practice
  • IMP – Investigational Medicinal Product
  • IVRS – Interactive Voice Response System
  • RA – Regulatory Authorities
  • Site-INV – Site-Investigator
  • SOP – Standard Operating Procedures
  • SP-INV – Sponsor-Investigator
  • SUSAR – Suspected Unexpected Serious Adverse Reaction
  • WI – Working Instructions
Set-Up ↦ Safety ↦ Safety Management ↦ Emergency Unblinding

Provides some background knowledge and basic definitions

Basic Monitoring
Basic Drug or Device

Starts with a study idea

Ends after having assessed and evaluated study feasibility

Concept Statistic Methodology
Concept Drug or Device

Starts with confidence that the study is feasible

Ends after having received ethics and regulatory approval

Development Drug or Device

Starts with ethics and regulatory approval

Ends after successful study initiation

Set-Up Ethics and Laws
Set-Up Statistic Methodology
Set-Up Quality and Risk
Set-Up Drug or Device

Starts with participant recruitment

Ends after the last participant has completed the last study visit

Conduct Statistic Methodology
Conduct Drug or Device

Starts with last study visit completed

Ends after study publication and archiving

Completion Statistic Methodology
Completion Drug or Device
Current Path (click to copy): Set-Up ↦ Safety ↦ Safety Management ↦ Emergency Unblinding

Please note: the Easy-GCS tool is currently under construction.