In clinical trials
Brain & sleep
Trofinetide
Before Rett syndrome approval, trofinetide was studied for Fragile X and traumatic brain injury. Here is what those investigational programs found.
- Reviewed by
- William Maish, MD MBA MPH, Clinical Product Lead
- Published
- October 5, 2026
- Last updated
- October 5, 2026
Key takeaway
Trofinetide is an IGF-1-derived peptide that is FDA-approved as DAYBUE for Rett syndrome, but its earlier "predecessor" programs, chiefly Fragile X syndrome and traumatic brain injury, were investigational and did not lead to approval. In Fragile X, a short exploratory trial reported only a preliminary signal that was never confirmed. This entry covers those investigational predecessor uses, not the approved Rett indication.
At a glance
| FDA status | FDA-approved as DAYBUE for Rett syndrome; other (predecessor) programs are investigational |
| What it is | Oral peptide analog of a fragment of IGF-1 |
| Fragile X | Program produced only a short exploratory signal and did not advance to approval |
| Brain injury | Traumatic brain injury program also did not succeed |
| Evidence strength | Low research (for the investigational predecessor programs) |
What is trofinetide?
Trofinetide is a synthetic analog of a small fragment of insulin-like growth factor-1 (IGF-1), taken by mouth, originated by Neuren Pharmaceuticals. It is approved by the FDA as DAYBUE for Rett syndrome, a rare neurodevelopmental disorder. Before that approval, it was also studied in other conditions, principally Fragile X syndrome and traumatic brain injury, and those earlier "predecessor" programs, the focus of this entry, remained investigational and did not reach approval.
How does it work?
As an IGF-1-related peptide, trofinetide is proposed to support synaptic maturation1 and to reduce neuroinflammation and dysfunction in the brain's support cells (glia). This mechanism underpins its development across several neurodevelopmental conditions. This describes the proposed mechanism; for the predecessor programs, the human outcomes did not support approval.
Is it FDA-approved?
For Rett syndrome, yes. For the investigational predecessor uses, no. Status by program:
| Program | FDA status |
| Rett syndrome | Approved, as DAYBUE |
| Fragile X syndrome | No approved indication |
| Traumatic brain injury | Not approved; the program did not succeed |
This entry concerns those unapproved uses; the approved Rett syndrome product is separate.
What does the research show?
For Fragile X, the evidence is a short exploratory trial. According to PubMed, a double-blind, placebo-controlled Phase 2 study1 in adolescent and adult males with Fragile X syndrome reported that the higher dose met prespecified exploratory efficacy criteria on several Fragile X-specific measures over a brief 28-day period, which the authors framed as a preliminary signal.
This program was not advanced to a successful registration trial, and trofinetide is not approved for Fragile X. Earlier work in traumatic brain injury likewise did not yield an approved indication. The predecessor-program evidence is limited and unconfirmed.
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Sources: the Phase 2 Fragile X syndrome trial (Berry-Kravis et al., Pediatric Neurology, 2020, DOI: 10.1016/j.pediatrneurol.2020.04.0191), indexed on PubMed; and the FDA approval of DAYBUE (trofinetide) for Rett syndrome. This document is educational, is not medical advice or a health claim, and is not an offer to sell any product.