Protocol deviations are a familiar part of clinical research, yet historically there has been little regulatory clarity around their classification and management. Clearer expectations for assessment, categorization, and reporting of these deviations are provided in a 2024 U.S. Food and Drug Administration (FDA) draft guidance document. There is a particular focus on “important” protocol deviations, defined by FDA as “a subset of protocol deviations that might significantly affect the completeness, accuracy, and/or reliability of the study data or that might significantly affect a subject’s rights, safety, or well-being.”
