The U.S. Food and Drug Administration on Thursday released more than 200 so-called complete response letters—formal notices explaining why the agency initially declined to approve new medicines—in its most sweeping transparency initiative to date. The documents, issued between 2020 and 2024, had previously been scattered across individual approval packets or withheld entirely. All of the published letters relate to drugs and biologics that ultimately won FDA clearance, and at least 14 are being disclosed for the first time, according to the agency. While many involve generic products, the cache also contains novel-drug correspondence, including a 2019 letter to AstraZeneca that highlighted efficacy shortcomings in one of its submissions. Commissioner Marty Makary said the release is aimed at ending “guessing games” for developers and investors. “Drug developers and capital markets alike want predictability,” he said, adding that clearer insight into the agency’s reasoning should speed future approvals and reduce repeated mistakes. Trade secrets and confidential commercial information were redacted, and letters tied to products that never reached the market remain unpublished. Attorneys and industry groups have signaled the policy could face legal challenges, but the FDA said additional batches of archived rejection letters are being prepared as part of its broader push for ‘radical transparency.’