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On April 6, 2026, Neurocrine Biosciences announced that it would commence a cash tender offer to acquire Soleno Therapeutics for $2.9 billion. This deal secured Vykat XR, the first and only FDA-approved treatment for hyperphagia in Prader-Willi Syndrome (PWS) in patients four years of age and older. Neurocrine CEO Kyle Gano remarked, “We share the Soleno team’s deep commitment to the Prader-Willi syndrome community and look forward to leveraging our experience and capabilities to expand Vykat XR’s reach to benefit more patients, while further strengthening Neurocrine’s leadership in delivering transformative medicines […] We congratulate Soleno on developing and launching Vykat XR, showing strong results in a complex disease and enabling broad utilization with a clear label, and we look forward to working together to continue to help patients in need.” Dr. Anish Bhatnagar, M.D., CEO of Soleno, emphasized that Neurocrine’s ‘strong commercial capabilities’ make them the right partner to scale Vykat XR’s reach.

Here, we expand on the history of Prader-Willi Syndrome (PWS) and the rollercoaster of clinical data that led to the FDA approval of Vykat XR.

Prader-Willi Syndrome (PWS) is a fascinating case study in how medical science transitioned from observing physical symptoms to unlocking the complexities of human genetics.

The syndrome was first identified by a team of Swiss pediatricians: Dr. Andrea Prader, Dr. Heinrich Willi, and Dr. Alexis Labhart, along with Dr. Guido Fanconi and Dr. Rudolf Ziegler. For many years, the condition was referred to as “Prader-Labhart-Willi Syndrome” before eventually being shortened to PWS. In 1956, they presented a clinical report describing nine children who shared a distinct pattern of symptoms that didn’t fit any known diagnosis at the time. Their initial observations included:

Our understanding of PWS has evolved through three distinct eras:

This proved that some genes “know” which parent they came from and are turned on or off accordingly.

The defining feature of PWS is a chronic, intense sensation of hunger. This drives compulsive food-seeking behavior, food preoccupation, and a lack of satiety. Hyperphagia leads to morbid obesity, diabetes, and cardiovascular disease. Acute risks include stomach rupture, choking, and accidental death related to food-seeking. The average lifespan for a PWS patient is approximately 30 years; 50% of deaths occur in patients under the age of 18, often due to respiratory or cardiovascular complications. PWS occurs in approximately 1 in 15,000 live births. There are an estimated 15,000 to 22,000 individuals living with PWS in the United States, with approximately 10,000 considered to be the initial addressable market for pharmacotherapy.

Modern management of Prader-Willi Syndrome (PWS) has shifted from a model of “crisis management” (dealing with obesity after it occurs) to a proactive, multidisciplinary strategy that begins at birth. It is a lifelong journey that changes significantly as the person moves through distinct “nutritional phases”.

During infancy (birth to 2 years old), the primary challenge is ironically the opposite of overeating. Babies are often too weak to eat. Diagnosis is prompted by “floppiness” (hypotonia) and a weak cry. DNA methylation testing is the gold standard, confirming PWS in >99% of cases. Most infants require a nasogastric (NG) or gastrostomy (G-tube) feeding tube because they lack the muscle strength to suck or swallow. Human growth hormone treatments a now standardly started as early as 3–6 months. This isn’t just for height; it improves muscle tone, respiratory function, and brain development. Physical and speech therapy begin almost immediately to hit motor milestones (like sitting or babbling) that are typically delayed by 50%.

During preschool & early childhood (ages 2 to 8 years), the child’s metabolism slows down, and their interest in food typically begins to climb. If diagnosis is missed at birth, occurs at this point due to global developmental delays or the sudden onset of rapid weight gain without a change in calories. Children with PWS typically need 20–30% fewer calories than their peers to maintain a healthy weight due to low muscle mass. Families begin implementing “no doubt” environments; locking pantries and using visual schedules so the child never has to wonder when the next meal is coming. As such, the burden on families is described as higher than that of Alzheimer’s disease, with 92% of siblings reporting moderate-to-severe symptoms of PTSD due to the disruptive and aggressive behaviors associated with the condition. While environmental controls begin early, pharmacological intervention with Vykat XR is specifically indicated for eligible patients within this group starting at four years of age.

During adolescence (ages 9 to 18 years), the drive for food peaks and is often accompanied by complex behavioral challenges and the absence of natural puberty. Since the hypothalamus doesn’t signal for puberty, teens receive testosterone or estrogen/progesterone to ensure bone health and sexual development. Screening for “skin-picking” (excoriation) and temper outbursts. Guanfacine or topiramate are often used to manage these obsessive-compulsive tendencies. Rapid growth and low muscle tone make scoliosis common; annual X-rays are standard during the teen growth spurt.

During adulthood (ages 18+ years), management shifts toward maintaining quality of life and preventing the life-threatening complications of obesity or gastric issues. Most adults thrive in “PWS-specific” group homes where food access is professionally managed, allowing them to focus on work or social life rather than food-seeking. Annual screening for psychosis, which occurs at higher rates in adults with the “maternal uniparental disomy” (mUPD) subtype of PWS. Separately, deletion (missing paternal material) is the most common PWS subtype (~60-70%). Since individuals with PWS rarely vomit, any sign of stomach pain or vomiting is treated as a surgical emergency (risk of gastric rupture).

In the decades following the discovery of PWS (1950s – 1980s), medical professionals viewed the condition primarily as an obesity disorder, with interventions aimed at weight loss at any costs. Treatments were often blunt and occasionally harsh, involving extreme low-calorie diets and physical restriction. Survival rates were low; many patients died in their 20s or 30s due to complications of morbid obesity (cardiac failure or respiratory issues).

The introduction of growth hormone (GH) therapy in the late 1990s – 2000s was the single most significant milestone in PWS history. Doctors realized that PWS wasn’t just about fat; it was about a lack of lean muscle and metabolic dysfunction. GH therapy (FDA-approved for PWS in 2000) allowed children to grow taller, develop better muscle tone, and improve their metabolic rate. This made weight management possible without starvation-level dieting.

The 2010s saw a shift in how the psychology of the syndrome was managed. Clinicians moved away from expecting the patient to control their hunger. Instead, the “Food Security” model became the standard, removing the “anxiety of the hunt” by locking kitchens and providing absolute meal predictability. There was an increased focus on the anxiety and OCD aspects of PWS, using medications like SSRIs to manage the “meltdowns” that often accompany the food drive.

As researchers began to understand the brain’s hunger pathways, several promising drugs entered trials but failed due to safety or funding issues:

The development of Vykat XR (diazoxide choline) is one of the most resilient “comeback stories” in modern pharmacology. It survived a failed Phase 3 trial and a global pandemic before becoming the first-ever FDA-approved treatment specifically indicated for hyperphagia associated with PWS in patients four years of age and older on March 26, 2025.

The journey began with diazoxide, a medication that has been used since the 1960s to treat high blood pressure and certain low blood sugar conditions. Researchers noticed that diazoxide could activate potassium channels in the brain’s hunger center (the hypothalamus). Soleno Therapeutics developed a proprietary crystalline salt version, diazoxide choline, and put it into an extended-release (XR) tablet. This was designed to provide a steady dose that could suppress hunger without the “peaks and valleys” of the original drug.

In June 2020, the development of the drug hit a major wall. The Phase 3 trial, called DESTINY PWS, failed to meet its primary endpoint, the Hyperphagia Questionnaire for Clinical Trials (HQ-CT). On paper, the drug didn’t seem to reduce hunger significantly more than a placebo. Soleno argued that the results were skewed by COVID-19. Because of lockdowns, families were home 24/7, providing “forced” food security that made the placebo group look better than they would have in a normal world. When the researchers looked only at data collected before the pandemic, the drug actually showed a statistically significant improvement in HQ-CT, the trial’s primary endpoint.

To prove the drug worked, the FDA asked for more data. Soleno used a clever trial design called a Randomized Withdrawal Study. They focused on 77 patients who had already been taking Vykat XR for years in an “open-label” study and were doing well. They then took half of those patients, switched them to a placebo, and observed the impacts on appetite. At the end of the 16-week randomized withdrawal study period, there was statistically significant worsening of hyperphagia in the placebo group relative to the Vykat XR group, as assessed by the HQ-CT Total Score (+2.6 points Vykat XR versus +7.6 points placebo, p < 0.001). This provided the “gold standard” proof the FDA needed.

After nearly a decade of development and orphan drug designations, the drug reached the finish line. On March 26, 2025, Vykat XR was officially approved for patients aged 4 and older. The most common adverse reactions observed in trials included hypertrichosis (increased hair growth), edema, and hyperglycemia. The FDA-approved labeling also includes a Warning and Precaution for the Risk of Fluid Overload; healthcare providers should monitor for signs of edema and use caution in patients with compromised cardiac reserve. Additionally, baseline testing of fasting plasma glucose and HbA1c is required prior to initiation, with regular monitoring thereafter to manage the risk of hyperglycemia. In addition to baseline testing of fasting plasma glucose and HbA1c, the prescribing label recommends monitoring fasting glucose weekly for the first two weeks of treatment, then every four weeks thereafter, to mitigate the risk of severe hyperglycemia or ketoacidosis. Additionally, the FDA-approved labeling notes that Vykat XR is contraindicated in patients with a known hypersensitivity to diazoxide or thiazides. For complete details on dosage, safety information, and contraindications, please consult the official FDA-approved labeling found here.

Following its Q2 2025 launch, it generated approximately $190 million in revenue for the year, including $92 million in Q4 2025 alone, indicating the patient/physician enthusiasm for Vykat XR within the first 9 months of launch. As of December 31, 2025, there were over 1,250 total new patient start forms for Vykat XR, representing approximately 12.5% of Soleno’s estimated 10,000-patient addressable launch population in the United States.

The announced acquisition of Soleno Therapeutics by Neurocrine Biosciences on April 6, 2026, is expected to represent a definitive turning point in the history of Prader-Willi Syndrome (PWS). For nearly seventy years, families and clinicians were left with few tools beyond physical locks and constant supervision to manage the relentless drive of hyperphagia. The journey of Vykat XR, from a repurposed blood pressure medication to a breakthrough therapy that survived the statistical anomalies of a global pandemic, serves as a testament to the resilience of rare disease research.

As Neurocrine Biosciences integrates Vykat XR into its portfolio, the focus shifts from proving the drug’s efficacy to ensuring its accessibility. With over 1,250 total new patient start forms recorded by the end of 2025, the “Food Security” model is finally being augmented by a therapeutic solution for patients four years of age and older. While patients with PWS continue to have unmet medical needs relating to their condition, the arrival of a treatment for hunger provides something vital: the possibility of a more manageable, independent, and dignified life for eligible patients four years of age and older with hyperphagia associated with PWS.

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