ACP-101 for Prader-Willi syndrome

Last updated Oct. 24, 2025, by Margarida Maia, PhD
Fact-checked by Marta Figueiredo, PhD

What was ACP-101 for Prader-Willi syndrome?

ACP-101 is an investigational nasal therapy that Acadia Pharmaceuticals was developing for reducing hyperphagia, or insatiable hunger, in people with Prader-Willi syndrome (PWS).

During childhood, PWS patients develop hyperphagia, which can lead to excessive weight gain and challenging behaviors, such as anger when seeking food or frustration when it is unavailable.

The active ingredient in ACP-101, carbetocin, is a lab-made version of the oxytocin hormone whose production is impaired in the brain of people with PWS. Oxytocin plays a critical role in appetite by sending fullness signals to the brain and helps regulate social and emotional behaviors.

By delivering carbetocin directly into the brain through a nasal spray, ACP-101 was expected to ease hyperphagia and its related behaviors, along with other behavioral symptoms in people with PWS.

ACP-101 was originally developed by Levo Therapeutics under the name LV-101. After acquiring the company in 2022, Acadia gained ACP-101’s development and commercial rights. The company discontinued its development after the therapy failed to show benefits in Phase 3 clinical testing.

Side effects reported with ACP-101 were mild or moderate in severity and included headache, flushing, nosebleeds, diarrhea, nasal discomfort, fever, and infection of the upper respiratory tract.

Therapy snapshot

ACP-101 in clinical trials

ACP-101 was initially tested in a Phase 2 clinical trial (NCT01968187) with 37 children and adolescents with PWS, and in a Phase 3 trial, called CARE-PWS (NCT03649477), that included 138 patients 7 to 18 years old.

In CARE-PWS, about two months of treatment with an ACP-101 dose of 9.6 mg, administered three times a day, was not significantly superior to the placebo at easing hyperphagia-related or obsessive-compulsive behaviors. This meant the trial failed to meet its main goals. Still, compared with the children on the placebo, those given the 3.2 mg dose showed a significant reduction in:

• hyperphagia-related behaviors
• anxiety and distress
• clinician’s perceived global disease severity

The U.S. Food and Drug Administration considered these results to be insufficient to grant approval to ACP-101 and asked for another trial to confirm its benefits. This prompted Acadia to launch another Phase 3 trial, called COMPASS PWS (NCT06173531).

The study tested the 3.2-mg dose against a placebo in 175 children and adults, ages 5 to 30, with PWS. Participants received their assigned treatment through the nose three times a day for about three months.

Its main goal was to watch for changes in the Hyperphagia Questionnaire for Clinical Trials score, a caregiver-reported measure of hyperphagia-related behaviors. Secondary goals included changes in clinicians’ and caregivers’ impressions of PWS severity.

Top-line data showed no significant differences between the ACP-101 and placebo groups in terms of the trial’s primary and secondary goals, indicating no considerable benefit from the investigational therapy. Based on these data, Acadia decided not to continue developing ACP-101.

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