On Wednesday, September 24, 2025, Acadia Pharmaceuticals shared an update on their Phase 3 COMPASS PWS trial, which evaluated intranasal carbetocin (ACP-101) for hyperphagia (excessive hunger) in children and adults with Prader-Willi syndrome (PWS).
The trial did not meet its primary endpoint of improving scores on the Hyperphagia Questionnaire for Clinical Trials (HQ-CT) from baseline to Week 12, nor did it show separation from placebo on any of its secondary endpoints. In other words, The trial results showed that the carbetocin drug did not make a meaningful enough difference in reducing hyperphagia compared to a placebo. While the safety and tolerability profile remained consistent with earlier trials, with a low rate of adverse events, Acadia announced they will not be moving forward with intranasal carbetocin development for PWS.
This is deeply disappointing news for our community. Hyperphagia is one of the most challenging symptoms of PWS, and every clinical trial brings hope for new treatment options. While these results are not what any of us had hoped for, we are grateful to Acadia Pharmaceuticals for the years of work they invested in this trial, and for their partnership and support of the PWS community and PWSA | USA.
Most importantly, we extend our heartfelt gratitude to the individuals living with PWS and their families who participated in the carbetocin trials. Your courage, commitment, and willingness to contribute to research bring us closer to a future with effective treatments. Even in disappointment, your role in advancing science and strengthening our shared hope cannot be overstated.
Acadia’s Head of Research and Development, Elizabeth H.Z. Thompson, Ph.D., shared in their announcement:
“We are disappointed by these findings, especially for Prader-Willi syndrome patients, their families and the entire community. I want to thank the many patients, families, study site personnel, and physicians who participated in the COMPASS PWS study as well as the intranasal carbetocin clinical development program, for their dedication and contributions in this important study. We are committed to sharing a summary of the data in the future to ensure learning for the PWS community; however, given these results, we do not intend to investigate intranasal carbetocin any further.”
At PWSA | USA, we know this news is hard to hear. Please remember, you are not alone. Our team is here to support you. If you need someone to talk to, you can reach us by phone at (941) 312-0400 or email us at info@pwsausa.org.
Together, we will continue on this journey of hope – supporting one another, advocating for research, and working toward a better future for all people living with PWS.
Read Acadia’s full press release by clicking the button below.
Following the difficult news about the COMPASS PWS study, Acadia Pharmaceuticals has shared a message with the Prader-Willi syndrome community. In it, they express deep gratitude to the families, individuals, and investigators who took part in this important trial. You can read their full letter at the button below.
Perry A. Zirkel has written more than 1,500 publications on various aspects of school law, with an emphasis on legal issues in special education. He writes a regular column for NAESP’s Principal magazine and NASP’s Communiqué newsletter, and he did so previously for Phi Delta Kappan and Teaching Exceptional Children.
Jennifer Bolander has been serving as a Special Education Specialist for PWSA (USA) since October of 2015. She is a graduate of John Carroll University and lives in Ohio with her husband Brad and daughters Kate (17), and Sophia (13) who was born with PWS.
Dr. Amy McTighe is the PWS Program Manager and Inpatient Teacher at the Center for Prader-Willi Syndrome at the Children’s Institute of Pittsburgh. She graduated from Duquesne University receiving her Bachelor’s and Master’s degree in Education with a focus on elementary education, special education, and language arts.
Evan has worked with the Prader-Willi Syndrome Association (USA) since 2007 primarily as a Crisis Intervention and Family Support Counselor. Evans works with parents and schools to foster strong collaborative relationships and appropriate educational environments for students with PWS.
Staci Zimmerman works for Prader-Willi Syndrome Association of Colorado as an Individualized Education Program (IEP) consultant. Staci collaborates with the PWS multi-disciplinary clinic at the Children’s Hospital in Denver supporting families and school districts around the United States with their child’s Individual Educational Plan.
Founded in 2001, SDLC is a non-profit legal services organization dedicated to protecting and advancing the legal rights of people with disabilities throughout the South. It partners with the Southern Poverty Law Center, Protection and Advocacy (P&A) programs, Legal Services Corporations (LSC) and disability organizations on major, systemic disability rights issues involving the Individuals with Disabilities Education Act (IDEA), Americans with Disabilities Act (ADA), and the federal Medicaid Act. Recently in November 2014, Jim retired.