FDA Approves First Treatment for Rett Syndrome
In March 2023, the FDA approved Daybue (trofinetide) as the first-ever treatment for Rett syndrome in adults and children 2 years and older. A clinical trial showed statistically significant improvement compared to placebo.
Research Profile
Published: March 13, 2023
Added to SpecialCircle: July 25, 2026
Evidence Level
Regulatory approval based on randomized, double-blind, placebo-controlled trialResearch Status
FDA-approved; based on completed Phase 3 clinical trial (NCT04181723)Key takeaways
- •Daybue (trofinetide) is the first FDA-approved treatment for Rett syndrome.
- •It is approved for adults and children aged 2 years and older.
- •It can be taken by mouth or through a gastrostomy tube, twice daily (morning and evening), with or without food.
- •The dose is based on the patient's weight.
- •In a 12-week clinical trial of patients aged 5 to 20, those taking Daybue showed a statistically significant improvement compared to those taking placebo on both co-primary measures.
- •The most common side effects were diarrhea (81% of treated patients) and vomiting (27%).
- •Daybue received priority review, orphan drug, and fast track designations from the FDA.
Source
U.S. Food and Drug Administration (FDA) · Government regulatory announcement
Read the original sourcePlain-language summary
The FDA has approved the very first medicine for Rett syndrome. It is called Daybue, and its scientific name is trofinetide.
This is a big deal because, until now, there was no FDA-approved treatment for this condition at all.
Daybue is approved for people aged 2 and older. It comes as a liquid that can be swallowed by mouth or given through a feeding tube.
It is taken twice a day — once in the morning and once in the evening — and the amount given depends on how much the patient weighs.
The FDA based this approval on a 12-week study of 187 patients between the ages of 5 and 20. Patients who took Daybue showed a statistically significant improvement compared to patients who took a placebo (a dummy treatment with no medicine).
The most common side effects were diarrhea and vomiting. Talk to your child's doctor to understand whether Daybue might be right for your child and what to watch for.
How it works
Science explained
The FDA announcement does not describe in detail how trofinetide works at a biological level. It identifies Daybue as an oral solution approved for Rett syndrome, a rare genetic neurological and developmental disorder that affects how the brain develops. Rett syndrome causes a progressive loss of motor skills and language, and its hallmark is near-constant repetitive hand movements. Speak with your child's neurologist for a deeper explanation of the drug's mechanism.
Why parents may care
Rett syndrome leads to severe impairments affecting nearly every aspect of life — the ability to speak, walk, eat, and breathe. Until this approval, there was no FDA-approved medicine specifically for this condition.
The approval of Daybue means there is now an officially reviewed and approved treatment option that showed measurable, statistically significant benefit in a rigorous clinical trial. For families who have been waiting for any approved option, this is a meaningful development.
What this means for daily life
If a doctor prescribes Daybue, a caregiver would give it as a liquid twice a day — morning and evening — with or without food. It can be given by mouth or through a gastrostomy tube if the child uses one.
The dose will be calculated based on the child's weight. Parents should be aware that diarrhea (reported in 81% of treated patients in the trial) and vomiting (27%) were the most commonly reported side effects.
Talking with your child's care team about managing these side effects and monitoring your child's response is important.
Clinical trial journey
Phase
Phase 3 (pivotal trial — NCT04181723)
Enrollment
Completed (trial supported the FDA approval granted March 2023)
Data collection
12-week randomized, double-blind, placebo-controlled study; co-primary endpoints were change from baseline in the Rett Syndrome Behavior Questionnaire (RSBQ) total score and the Clinical Global Impression-Improvement (CGI-I) score at week 12
Preliminary results
Patients treated with Daybue demonstrated a statistically significant difference compared to placebo on both co-primary efficacy endpoints (RSBQ total score and CGI-I score) at week 12. Most common adverse reactions were diarrhea (81%) and vomiting (27%).
Regulatory / next steps
Daybue is now FDA-approved and available by prescription. Ongoing post-market data collection will continue to build long-term safety and efficacy information.
Who may be eligible
The pivotal trial enrolled patients with Rett syndrome aged 5 to 20. The FDA approval covers adults and children 2 years of age and older.
What is still unknown
The clinical trial that supported FDA approval studied patients aged 5 to 20 for 12 weeks. It is not yet known how well Daybue works over longer periods of time, in children under 5, or in adults older than 20.
Long-term safety data are still being gathered. The full prescribing information contains additional details on risks, and ongoing real-world use will continue to build the evidence base.
Frequently asked questions about Rett Syndrome
Daybue is the brand name for trofinetide, an oral solution (liquid medicine). It is the first FDA-approved treatment specifically for Rett syndrome.
Terminology glossary
- Trofinetide (Daybue)
- The first FDA-approved medicine for Rett syndrome, given as a liquid twice daily by mouth or feeding tube, with the dose based on patient weight.
- Gastrostomy tube
- A feeding tube inserted through the abdomen directly into the stomach, used when someone cannot eat or swallow by mouth.
- Randomized, double-blind, placebo-controlled trial
- A type of clinical study considered highly reliable. Patients are randomly assigned to receive either the real treatment or a placebo (inactive treatment), and neither the patients nor the researchers know who is getting which until the study ends.
- RSBQ (Rett Syndrome Behavior Questionnaire)
- A 45-item rating scale completed by a caregiver that measures the range and severity of signs and symptoms of Rett syndrome. Lower scores mean less severe symptoms.
- CGI-I (Clinical Global Impression-Improvement)
- A 7-point scale rated by clinicians to assess how much a patient's condition has improved or worsened. A lower score indicates improvement.
- Orphan drug designation
- A special FDA status given to medicines that treat rare diseases affecting fewer than 200,000 people in the United States. It provides incentives to encourage development of treatments for rare conditions.
- Priority review
- An FDA designation that speeds up the review process for medicines that offer major advances in treatment or provide a treatment where no adequate therapy exists.
- Statistically significant
- A result in a study that is unlikely to have occurred by chance, giving researchers greater confidence that the treatment had a real effect.
Questions to ask your doctor or therapist
- ?Is Daybue appropriate for my child given their age, weight, and current health?
- ?How will we measure whether Daybue is working for my child?
- ?What should I do if my child experiences diarrhea or vomiting?
- ?Are there other risks I should know about beyond diarrhea and vomiting?
- ?How long would my child need to take Daybue before we know if it is helping?
- ?Where can I find the full prescribing information for Daybue?
⚕️ This research digest is for educational and community support purposes only. It is not medical advice, diagnosis, or treatment. Always speak with a qualified doctor, therapist, or medical professional before making decisions about care.
Related research
Understanding Real-World Use of Trofinetide for Rett Syndrome
This study looked at how people with Rett syndrome in the United States used trofinetide, an FDA-approved treatment, over time.
Understanding Who Receives Trofinetide for Rett Syndrome in the U.S.
A study found that only about one-quarter of eligible individuals with Rett Syndrome received the newly approved medication, Trofinetide, shortly after its approval in the United States.
Update on the NGN-401 Gene Therapy Study
Researchers have finished giving the study treatment to all 25 children in a major trial for a new gene therapy called NGN-401.
Understanding Sleep Challenges and Daytime Behavior in Rett Syndrome
A recent review explains how sleep disturbances are common in Rett Syndrome and how they relate to a child's mood and behavior during the day.
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