The Investigator Brochure sits at the center of some of the most consequential safety decisions in your trial, yet teams often treat it as background paperwork updated reluctantly and late. The IB does three critical things: it gives you the clinical context to understand why the protocol is designed the way it is, it defines which adverse reactions count as "expected" through its Reference Safety Information section, and it's a required submission to your IRB.
That second function matters most operationally. Whether a serious adverse reaction becomes a reportable SUSAR depends entirely on whether it appears in the RSI at the observed severity. The MHRA inspectorate recently documented critical findings at eight organizations where outdated IBs led to unreported SUSARs and missing risk mitigation measures. These weren't administrative slip-ups, they were patient safety failures.
ICH E6(R3), finalized in January 2025, requires the IB to be reviewed at least annually and revised whenever new safety information emerges. U.S. regulations at 21 CFR 312.55 require sponsors to provide investigators with a current IB before the trial starts and to update it as the evidence base evolves. Sites should confirm they're working from the current version, especially after protocol amendments.