A code-break procedure is a set of rules which determine when planned unblinding should occur in a blinded experiment.
A code-break procedure should only allow a participant to be unblinded before the conclusion of a trial in the event of an emergency.
Traditionally, each patient's treatment allocation data was stored in a sealed envelopes, which was to be opened to break code.
[2][3] As of 2016[update], sealed envelopes were still in use in some clinical trials.
[4] Modern clinical trials usually store this information in computer files.