Daybue (trofinetide) for Rett syndrome

Last updated Oct. 9, 2025, by Marisa Wexler, MS
Fact-checked by Jose Lopes, PhD

What is Daybue for Rett syndrome?

Daybue (trofinetide) is a daily treatment for people with Rett syndrome, ages 2 and older. It has been shown in trials to reduce the severity of Rett symptoms. The therapy, which is sold by Acadia Pharmaceuticals, can be taken by mouth or via a feeding tube.

The therapy’s active ingredient is an analog of insulin-like growth factor-1 (IGF1), a signaling molecule that helps regulate the development of brain cells. It’s thought that Daybue may help nerve cells form healthier connections, or synapses, and reduce inflammation in the brain.

Therapy snapshot

Who can take Daybue?

Daybue is approved by the U.S. Food and Drug Administration (FDA) to treat people with Rett syndrome ages 2 and older. It is similarly approved in Canada.

The prescribing information for Daybue does not list any contraindications.

How is Daybue administered?

Daybue is a liquid that may be taken orally or administered by a feeding tube. It is taken twice daily at a dosage determined based on the patient’s weight. The therapy may be taken with or without food.

Daybue in clinical trials

The FDA’s approval of Daybue was based on data from a Phase 3 clinical trial called LAVENDER (NCT04181723). The study tested the therapy against a placebo in 187 people, ages 5 to 20, with Rett syndrome.

• The results showed that, after 12 weeks, or about three months, patients given Daybue had significantly greater improvements on the Rett Syndrome Behaviour Questionnaire (RSBQ), a caregiver-rated assessment of the severity of Rett symptoms. The RSBQ measures symptoms such as repetitive hand movements and facial expressions. Significantly greater improvements were also seen on the Clinical Global Impression Scale-Improvement (CGI-I), a clinician-rated measure of overall health.

Some participants who completed the LAVENDER study continued to receive Daybue in the extension studies LILAC-1 (NCT04279314) and LILAC-2 (NCT04776746). Long-term data from these studies indicated that RSBQ and CGI-I scores tended to continue improving over several years of Daybue treatment.

A Phase 2/3 study called DAFFODIL (NCT04988867) tested Daybue in 15 children with Rett syndrome, ages 2 through 4. Those results indicated that the treatment led to improvements in CGI-I scores and measures of life quality.

Daybue side effects

The most common side effects associated with Daybue in clinical trials were vomiting and diarrhea.

Patients who experience severe diarrhea, vomiting, or weight loss may need to pause treatment, reduce their dose, and/or discontinue the therapy. The use of laxatives should be stopped before starting Daybue.

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