Neurocrine Biosciences is pushing back against growing safety concerns surrounding Vykat XR, its rare disease drug acquired in a $2.9 billion buyout of Soleno Therapeutics last spring.
A group of clinicians with deep ties to the Prader-Willi syndrome community has flagged potential safety signals associated with the drug, which became the first approved treatment for hyperphagia in PWS in March 2025.
Vykat XR, known generically as diazoxide choline, is a potassium channel activator approved to treat the sensation of insatiable hunger in patients with Prader-Willi syndrome.
Since the drug became more widely available, reports posted to the FDA’s Adverse Event Monitoring System include seven deaths and more than 100 other serious adverse events, mostly tied to edema, respiratory, and cardiac complications.
The adverse event trend was flagged in a statement from the Foundation for Prader-Willi Research, the International Prader-Willi Syndrome Organization, and Prader-Willi Syndrome USA, backed by the insights of seven PWS clinicians.
The patient organisations noted that cases resulting in death or serious outcomes were marked by “complex medical issues,” multiple medications, and, in many instances, pre-existing obesity.
“It cannot be determined from these adverse event reports whether these deaths and complications are directly related to VYKAT XR treatment or if they are part of the underlying challenges of PWS,” the clinician statement reads.
The clinicians also noted that these complications do not appear common among individuals providing data to the caregiver-reported outcomes in the Global PWS Registry, though they acknowledged that population may differ from the Vykat XR-treated group.
Neurocrine, for its part, continues to stand behind the drug, with a spokesperson saying Vykat XR boasts “a compelling risk-benefit profile in the context of a very serious disease.”
The company said it “conducted extensive diligence on the safety profile, including adverse event data, during our process to acquire Soleno,” and added that it remains closely engaged with the FDA, patient advocacy communities, and prescribers.
The clinician letter stopped well short of drawing a causal link between Vykat XR and the deaths and side effects reported to the FDA.
Clinicians noted that many medical complications are common in people with PWS, particularly when patients are dealing with obesity and uncontrolled sleep apnea.
“Compared to the general population, mortality is higher at all ages in people with PWS, and published data suggest that each year 1-3% of people with PWS die in all age groups,” the letter states.
The clinician statement calls for further study into potential risk factors including severe obesity, underlying heart problems, pre-existing edema, serious breathing issues, and poorly controlled sleep apnea.
“There may be other risk factors of which we are not yet aware,” the letter writers said, urging greater caution as the prescribing population continues to expand.
Despite the concerns, patient groups expressed gratitude toward drugmakers for developing new treatments and called for long-term follow-up clinical studies focused on safety and efficacy.
Neurocrine’s share price fell more than 3% on Thursday morning after the US market opened, reflecting investor unease over the safety questions surrounding the drug.
Neurocrine announced in April 2026 that it would acquire Soleno and its blockbuster-hopeful drug for $2.9 billion, with the deal closing on May 18.
While Evercore ISI analysts agreed that the “timing, asset profile, and role” of Vykat XR fit well within the Neurocrine narrative, other analysts expressed more skepticism about the drug’s long-term sales prospects at the time of the deal announcement.