AMX0035

Amylyx is a biotech company in Cambridge, Massachusetts, that developed AMX0035 with ALS researchers at Massachusetts General Hospital. After PHOENIX failed, it removed the drug from the market and restructured the company around other medicines in its pipeline.

Sodium phenylbutyrate and taurursodiol were each thought to reduce two kinds of stress inside nerve cells: in the endoplasmic reticulum, where proteins are folded, and in the mitochondria, which make energy. The idea was that together they might keep motor neurons alive longer.

Health Canada gave conditional approval in June 2022 and the FDA approved it in September 2022, both before a confirmatory trial was finished. The EU refused approval in January 2024. After PHOENIX failed, Amylyx withdrew the drug in April 2024, and the FDA's withdrawal of approval took effect on August 29, 2025.

PHOENIX was meant to confirm the CENTAUR results but showed no benefit after 48 weeks. Amylyx announced it would remove Relyvrio and Albrioza from the market less than a month later. This is one of the clearest examples of a promising smaller trial not holding up in a larger one.

The earlier CENTAUR trial (137 people, 24 weeks) reported ALSFRS-R decline of 1.24 points a month on the drug versus 1.66 on placebo, with no difference in strength, breathing or survival measures. The much larger PHOENIX trial (664 people, 48 weeks) found no difference from placebo: scores fell 14.98 points on the drug and 15.32 on placebo. Secondary goals, including breathing, quality of life and later survival, also showed no clear difference, including in people who resembled the CENTAUR participants. The PHOENIX result is the more reliable one.

This is the most favourable result reported. See all key studies for the full picture.

AMX0035 was tested in adults with definite ALS whose symptoms had started within the previous 18 months, not a specific genetic type. In CENTAUR it was taken once a day for three weeks and then twice a day. It is no longer prescribed for new patients.

AMX0035 is no longer sold. When it was withdrawn in April 2024, Amylyx said people already taking it who wished to continue, after talking with their doctor, could move to a free drug programme. No ALS trials of AMX0035 are recruiting.