Acadia's Rett Syndrome Drug Nears EU Approval After Regulatory Reversal

SAN DIEGO, CA – June 26, 2026 – After a challenging regulatory journey, a new therapy offering hope to thousands of families affected by Rett syndrome is on the verge of becoming a reality in Europe. San Diego-based Acadia Pharmaceuticals announced that the European Medicines Agency's (EMA) Committee for Medicinal Products for Human Use (CHMP) has issued a positive opinion for DAYBU® (trofinetide), recommending its approval for treating the neurobehavioral symptoms of the rare genetic disorder.

The recommendation, which covers adults and children aged five and older, positions DAYBU® to become the first-ever approved treatment for this indication in the European Union. For a community that has long navigated a landscape devoid of targeted therapies, the news represents a potential paradigm shift. The European Commission is expected to issue a final decision in the coming months, a move that would grant marketing authorization across all 27 EU member states, plus Iceland, Liechtenstein, and Norway.

A Beacon for a Community in Need

Rett syndrome is a complex and devastating neurodevelopmental disorder, occurring in approximately one in every 10,000 to 15,000 female births. After a period of seemingly normal development, children experience a rapid regression, losing acquired skills like speech and purposeful hand use. The condition leads to a lifetime of severe impairments, requiring intense, round-the-clock care.

Until now, management in Europe has been purely symptomatic, a fragmented collection of therapies for seizures, digestive issues, and motor difficulties. The core neurobehavioral symptoms, however, have remained unaddressed by any approved medicine.

“For decades, families in Europe affected by Rett syndrome have had no medicine specifically approved for the neurobehavioral symptoms of this condition, despite the profound impact they have on almost every aspect of daily life,” said Pedro Rocha, President of Rett Syndrome Europe, in a statement. “The CHMP’s positive opinion represents hope for thousands of European Union individuals living with this devastating condition, their families and caregivers."

The burden on caregivers is immense. Studies from patient advocacy groups like Rett Syndrome Europe have consistently highlighted the fragmented care, delayed diagnoses, and significant personal and financial strain faced by families across the continent. This positive opinion is more than just a regulatory milestone; it's a validation of years of advocacy and a powerful symbol of progress for a community that has often felt overlooked.

From Rejection to Recommendation: A Story of Regulatory Resilience

Acadia's path to this point was not straightforward, underscoring the high-stakes, complex nature of bringing orphan drugs to the European market. The CHMP initially issued a negative opinion on DAYBU® in February 2026, concluding that the treatment effects observed in clinical trials were not "clinically meaningful enough" at that stage.

Rather than abandoning its European ambitions, Acadia initiated a formal re-examination procedure. This move allowed the company to present further arguments and clarifications to address the committee's concerns. The subsequent reversal to a positive opinion is a significant strategic victory for the biopharmaceutical firm and a testament to the robustness of its clinical data.

“The CHMP’s positive opinion for DAYBU® is an important milestone in our mission to bring this innovative therapy to the EU," stated Catherine Owen Adams, Acadia’s Chief Executive Officer. "Our commitment is to make a meaningful difference in the lives of patients, caregivers, and the wider Rett community... and we are very pleased with the outcome of the re-examination process."

This successful navigation of the EMA’s rigorous review process offers a case study in operational and regulatory persistence. For a company broadening its focus from Parkinson's disease psychosis to a wider portfolio of neurological and rare diseases, securing a foothold in the lucrative European market is a critical component of its growth strategy.

The Science Behind the Shift

The foundation of the CHMP's recommendation rests on the Phase 3 LAVENDER™ study, a rigorous trial involving 187 girls and young women with Rett syndrome. The study demonstrated statistically significant and clinically meaningful improvements on two key measures: the Rett Syndrome Behaviour Questionnaire (RSBQ), a caregiver assessment of symptoms, and the Clinical Global Impression-Improvement (CGI-I) scale, a clinician's evaluation of overall change.

DAYBU® (trofinetide) is a synthetic analog of a naturally occurring peptide in the brain that is critical for neuronal development and function. Rett syndrome is typically caused by a mutation in the MECP2 gene, which is thought to impair synaptic communication. Trofinetide is believed to work by potentially reducing inflammation and improving the health of these vital connections between nerve cells, thereby addressing some of the core symptoms of the disorder. The positive LAVENDER™ results, backed by long-term data from open-label extension studies, provided the compelling evidence needed to sway the regulatory committee during the re-examination.

The Next Challenge: Market Access and Commercialization

While regulatory approval is the immediate prize, Acadia's next operational challenge is navigating the labyrinthine world of European market access. The continent's orphan drug market is projected to grow exponentially, with the Rett syndrome segment alone forecast to expand from just over $14 million in 2024 to more than $2 billion by 2032.

Capturing a significant share of this market requires more than just a green light from the EMA. Acadia must now engage in country-by-country negotiations on pricing and reimbursement. Each of the 27 EU member states has its own Health Technology Assessment (HTA) body, with unique standards for evaluating a drug's cost-effectiveness and budget impact. Germany, Europe's largest market, may be an early adopter, but securing access in all territories will be a complex, multi-year operational endeavor.

Having successfully launched DAYBU® in the United States and Canada, Acadia has a playbook to draw from. However, the company will need to demonstrate not just the clinical value shown in the LAVENDER™ study, but also how the therapy can reduce the overall burden of illness—including the immense, often unquantified, costs associated with round-the-clock caregiving. The journey from a positive CHMP opinion to widespread patient access is the next critical phase in Acadia's European gambit.