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# FDA Rare Disease Evidence Principles
- URL: https://www.fdaweb.com/fda-rare-disease-evidence-principles/
- Published: 2025-09-03T12:00:00.000Z
- Updated: 2026-09-14T15:20:48.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5159803

FDA has launched its Rare Disease Evidence Principles (RDEP) process to “provide greater speed and predictability in the review of therapies intended to treat rare diseases with very small patient populations with significant unmet medical need and that are driven by a known genetic defect.” An agency [statement](https://www.fda.gov/news-events/press-announcements/fda-advances-rare-disease-drug-development-new-evidence-principles?ref=fdaweb.com) says that through the RDEP process, sponsors will receive clearer guidance on the types of evidence that can be used to demonstrate substantial evidence of effectiveness.

The statement quotes FDA commissioner **Martin Makary** as saying that the principles “ensure that FDA and sponsors are aligned on a flexible, common-sense approach within our existing authorities, and that we incorporate confirmatory evidence to give sponsors a clear, rigorous path to bring safe and effective treatments to those who need them most.”

CDER and CBER jointly developed and implemented RDEP, the statement says, to address the inherent uncertainties of rare disease drug development by assuring sponsors that reviews will encompass additional supportive data. It says that approval under the process may be based on one adequate and well-controlled study plus robust confirmatory evidence, which may include strong mechanistic or biomarker evidence; evidence from relevant non-clinical models; clinical pharmacodynamic data; and case reports, expanded access data, or natural history studies.

FDA says sponsors may apply to the process any time before the launch of a pivotal trial. To be eligible, it says, investigative therapies must specifically address the genetic defect in question and target a very small rare disease population or subpopulation, generally fewer than 1,000 U.S. patients, facing rapid deterioration in function leading to disability or death, for whom no adequate alternate therapies exist.

The agency cautions that drugs approved through the RDEP process may face additional postmarketing requirements to further ensure safety and effectiveness.