George Tidmarsh resigned as director of the FDA’s Center for Drug Evaluation and Research after being placed on administrative leave amid an HHS investigation into his conduct. The departure follows allegations that he used regulatory authority against a former business associate and public disputes over drug-review policy. Tidmarsh had led CDER for roughly three months after a July appointment; his exit creates another leadership vacuum at the center amid a year of senior-level turnover. Industry and policy watchers say the personnel upheaval raises short-term uncertainty about review timelines and policy continuity at an agency central to drug approvals. The agency and HHS cited ‘‘serious concerns about his personal conduct’’; Tidmarsh has disputed wrongdoing in public comments. Companies with pending submissions and sponsors of high-stakes programs are watching for interim leadership decisions that could affect regulatory interactions and review cadence.