The FDA issued a complete response letter (CRL) for Biohaven’s troriluzole (Vyglxia) application in spinocerebellar ataxia, citing concerns with reliance on externally controlled real‑world evidence and potential bias from that study design. In response the company announced plans to cut annual R&D spending by roughly 60% and to focus on a narrowed set of late‑stage programs. Biohaven had argued the large, long‑duration real‑world evidence dataset showed robust effects; the agency highlighted confounding factors inherent in externally controlled trials and requested further discussions on acceptable evidence for approval. The CRL triggered immediate strategic changes at Biohaven, including program reprioritization and cost reduction measures. For rare‑disease developers, the decision underscores regulatory limits on substituting external controls for randomized trials and the need for early, formal alignment with regulators on evidence expectations.