Prader-Willi syndrome experts raise safety concerns over Neurocrine's Vykat XR

On August 11, 2026, Prader-Willi syndrome advocacy groups and experts raised safety concerns regarding Neurocrine Biosciences' newly approved drug Vykat XR. Post-marketing surveillance data from the FDA's Adverse Event Monitoring System revealed seven patient deaths as of July 31, 2026, alongside over 100 reports of serious adverse events like edema and respiratory issues. Neurocrine, which acquired the drug via a $2.9 billion buyout of Soleno, defended Vykat XR's risk-benefit profile.

Vykat XR safety concerns

• ▪Reported serious adverse events associated with Vykat XR since its post-marketing release include peripheral edema, respiratory complications, and cardiac complications.
• ▪A group of Prader-Willi syndrome physicians and experts notified clinicians on August 11, 2026, of patient deaths and severe side effects potentially associated with the drug Vykat XR.
• ▪Neurocrine Biosciences' shares fell 6.1% in premarket trading on August 12, 2026, following reports of safety concerns associated with Vykat XR.

Prader-Willi syndrome hyperphagia

• ▪Prader-Willi syndrome is a rare genetic disorder caused by deletions on chromosome 15 that causes hyperphagia, an insatiable and persistent desire to eat.
• ▪The Food and Drug Administration approved Vykat XR in March 2025 to treat hyperphagia in children and adults with Prader-Willi syndrome.

FDA adverse event data

• ▪The Food and Drug Administration's Adverse Event Monitoring System showed seven reports of death linked to patients taking Vykat XR as of July 31, 2026.
• ▪The Food and Drug Administration's Adverse Event Monitoring System received more than 100 reports of serious adverse events for Vykat XR, with peripheral edema and drug ineffectiveness being the highest reported reactions.

Neurocrine response to reports

• ▪Neurocrine Biosciences stated that Vykat XR has a compelling risk-benefit profile in the context of a very serious disease.
• ▪Neurocrine Biosciences stated it is actively engaged with the Food and Drug Administration, patient advocacy communities, and prescribers to assess post-marketing surveillance data for Vykat XR.

Advocacy group transparency statement

• ▪The Foundation for Prader-Willi Research and the International Prader-Willi Syndrome Organisation issued a joint statement on August 11, 2026, to encourage informed prescribing, careful patient selection, and close monitoring of Vykat XR.
• ▪The joint statement by Prader-Willi syndrome advocacy groups stressed that the adverse event reports do not establish a causal relationship between Vykat XR and the reported patient deaths or complications.

Soleno acquisition by Neurocrine

• ▪Neurocrine Biosciences acquired Soleno for $2.9 billion in 2026 to gain access to the Prader-Willi syndrome drug Vykat XR.
• ▪During the acquisition process of Soleno, Neurocrine Biosciences conducted extensive diligence on the safety profile of Vykat XR, including adverse event data.

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