Not Yet RecruitingPhase 3

A Phase 3 Study of Fenfluramine Hydrochloride in Rett Syndrome

United States, Hungary, Japan200 participantsStarted 2026-06-30

Plain-language summary

The purpose of this study is to investigate the efficacy of fenfluramine hydrochloride (HCl) versus placebo in study participants with Rett syndrome (RTT).

Who can participate

Age range

5 Years – 35 Years

Sex

ALL

See this in plain English?

AI-rewrites the medical criteria so a patient or caregiver can understand them. Always confirm with the trial site.

Exclusion criteria

. Greater than trace aortic valve regurgitation.
. Greater than mild mitral valve regurgitation.
. Possible signs of pulmonary arterial hypertension (PAH) with abnormal pulmonary artery systolic pressure (PASP) or PASP ≥35 mmHg.
. Evidence of left ventricular dysfunction (systolic or diastolic).
. Clinically significant structural cardiac abnormality, including but not limited to mitral valve prolapse, atrial or ventricular septal defects, or patent ductus arteriosus with reversal of shunt (right to left shunt). Note: Patent foramen ovale without a reversal of shunt or a bicuspid aortic valve is not considered exclusionary

Questions worth asking your doctor

Bring these to your next appointment. They're a starting point for a shared conversation — not a sign you qualify or a recommendation to enrol.

1Based on my diagnosis and history, is this trial worth exploring for me — or is there a standard treatment we should try first?
2What does this trial's phase tell us about how much is already known about its safety and benefit?
3What would taking part actually involve for me — visits, tests, time, and travel?
4What are the known and possible risks or side effects I should weigh, and how would they be monitored?
5If this trial isn't the right fit, what other options or trials would you suggest I look into?

Generated to help you prepare — always confirm anything about your own eligibility and care with the study team and your doctor.

Questions for the trial coordinator

The trial coordinator is the person who runs the study day to day. These cover the practical side — logistics, costs, and what taking part would actually mean for your life. The study team confirms whether you meet the criteria; these are questions to ask, not a sign you qualify.

1What does taking part actually involve week to week — how many visits, where, and how long does each one take?
2What costs are covered by the study, and what might I have to pay for myself, including travel, parking, or time off work?
3What happens during screening, and what happens if the study team confirms I don't meet the criteria after those tests?
4Who pays for the scans, blood work, and other tests the trial requires — the study, my insurance, or me?
5How will being in the trial affect my regular care, and will my own doctor stay informed and involved?
6Can I leave the trial at any point if I change my mind, and what would happen to my care if I do?

A starting point for the conversation — always confirm anything about your own eligibility, costs, and care with the study team and your doctor.

What they're measuring

Change from Baseline to Week 14 in Rett Syndrome Behaviour Questionnaire (RSBQ) Total Score

Timeframe: From Baseline (Day 1) to Week 14

Clinical Global Impression of Change (CGIC) Score at Week 14

Timeframe: At Week 14

Trial details

NCT IDNCT07503444

SponsorUCB BIOSCIENCES, Inc.

Sponsor typeINDUSTRY

Study typeINTERVENTIONAL

Primary completion2028-08-01

Contact for this trial

UCB Cares

+18445992273 ucbcares@ucb.com

View on ClinicalTrials.gov More Rett Syndrome trials