ALS has one of the highest-profile unmet needs in neurology, and Relyvrio’s approval became a defining test of how much regulatory flexibility that justifies.
The oral powder combined sodium phenylbutyrate and taurursodiol, intended to slow motor neuron death by easing endoplasmic reticulum and mitochondrial stress. Approval for amyotrophic lateral sclerosis rested on a small phase 2 trial after an initially negative advisory committee vote.
Amylyx withdrew Relyvrio from the market in April 2024 after the larger phase 3 PHOENIX trial missed its endpoints, and the application was formally withdrawn in 2025. It is now the central case study in regulatory flexibility for neurodegenerative disease.
