Peptide dossier, updated Oct 31, 2026
Dihexa
A synthetic peptide-like molecule derived from angiotensin IV. Dihexa is N-hexanoic-Tyr-Ile-(6)aminohexanoic amide. Every study of it we found is in animals or cells, and the key paper on its proposed mechanism has been retracted. FDA says it found no human exposure data. This page lays out what each source actually says.
See all 12 verified records for Dihexa on the Records page
Human studies
ClinicalTrials.gov returns no study listing dihexa as of Oct 31, 2026, and we found no published human study of it. Athira Pharma says its drug candidate fosgonimeton (ATH-1017) is a prodrug that metabolizes into dihexa. See SEC filings below. We did not review the trials of that candidate.
Registry entries are written by the sponsors and are not reviewed for scientific merit. A trial of a related compound does not tell us what happens when dihexa itself is taken.
FDA review
FDA’s safety-risk page (content current Apr 22, 2026) is the one FDA document on dihexa that we read.
What FDA’s page says
- FDA lists “dihexa acetate” among bulk drug substances that were nominated and later withdrawn, previously in category 2 under its interim compounding policies.
- It says it has not identified any human exposure data on drug products containing dihexa acetate administered via any route.
- It says it lacks important information on any safety issues raised by dihexa acetate, including whether it would cause harm if administered to humans.
What we did not find
- We found no FDA briefing document or advisory committee evaluation for dihexa. FDA’s notice for the July meeting does not name it, so the safety-risk page entry is the only FDA statement on it that we read.
- The page names the acetate. We found no FDA statement on the free base.
Published research
PubMed returns 18 results for “dihexa” in the title or abstract. We found no human study. The two foundational papers carry editorial notices.
What the papers show
- Design, 2013. Describes modifying a short angiotensin IV fragment into dihexa, reported as orally active and able to cross the blood-brain barrier, with antidementia-type effects in laboratory memory tests. The journal published a notice of concern on it in Sep 2021. J Pharmacol Exp Ther PubMed
- Mechanism, 2014. Reports that dihexa binds hepatocyte growth factor and that its effects depend on the HGF/c-Met system. The journal published a notice of concern in Sep 2021 and a retraction notice in Apr 2025. J Pharmacol Exp Ther PubMed
- Alzheimer’s mouse model, 2021. A separate group reports dihexa restored spatial learning in APP/PS1 mice and reduced markers of inflammation. Brain Sci PubMed
Read with care
- The retraction and the two notices of concern are in PubMed. The PubMed record does not show the reason, and we have not read the notices, so we do not state it. Athira’s own statement is below.
- The paper reporting the HGF/c-Met mechanism has been retracted. Papers that build on it may rely on it; we did not check.
- Everything we found is in animals or cells. FDA found no human data.
- We read abstracts only, not full text, funding or author disclosures.
FDA warning letters
We did not find an FDA warning letter that names dihexa. Warning letter 594743, which names several other peptides on this site, does not list it.
This rests on web searches, not a full pull of FDA’s database. FDA’s list of letters cannot be searched by peptide, so a letter could exist that we did not find.
SEC filings
Athira Pharma, Inc. licensed dihexa and is the filer we found. It changed its name to LeonaBio, Inc. in Jan 2026. EDGAR’s full-text search was not available to us, so this rests on web searches of sec.gov.
| Filer | Filing | What it says |
|---|---|---|
| Athira Pharma, Inc. (now LeonaBio, Inc.) | Form 8-K Filed Oct 21, 2021 | Says its lead candidate ATH-1017 is a prodrug that metabolizes rapidly in plasma into dihexa, a compound discovered at Washington State University (WSU) and exclusively licensed to the company. Says that from 2011 to 2015 it sought to develop dihexa, that its studies showed activity on HGF/MET but failed to show the characteristics of a successful therapeutic, and that development of dihexa was discontinued. Announces completion of an independent special committee investigation and leadership changes. |
| Athira Pharma, Inc. | Form 10-K, fiscal 2023 Filed Feb 22, 2024 | Says the special committee found that its former chief executive officer altered images in the officer’s 2011 doctoral dissertation and in at least four co-authored research papers published from 2011 to 2014. It says the company cited challenged papers in certain communications and applications, and that WSU’s dihexa patent, exclusively licensed to the company, incorporated certain of the altered images. It says WSU had begun a review and the company could not predict the outcome. |
What a company says in a filing is its own claim about its business. We read the passages naming dihexa and the committee’s findings, not the whole documents. The filing does not say which papers it means, and we have not matched them to the papers above. We do not name individuals in this dossier.
Timeline
Newest first. Every entry links to the document it comes from.
- Government or registry record
- Journal
- Oct 30, 2026RegulatoryHHS publishes draft policy pausing enforcement on six peptides; Dihexa is not one of them
Per two law-firm summaries the six are BPC-157, TB-500, epitalon, Semax, KPV and MOTS-c. The policy is a draft and not FDA approval. We could not open the policy attachment, so this rests on the summaries.
- July 23–24, 2026RegulatoryFDA advisory committee meets on seven peptides; Dihexa is not among them
The committee recommended six of the seven, all nonbinding. FDA’s notice of the meeting does not list Dihexa.
- Apr 22, 2026RegulatoryFDA’s safety-risk page lists Dihexa
FDA says it has found no human exposure data for dihexa acetate by any route.
- Apr 2025LiteratureJournal retracts the 2014 paper on dihexa’s mechanism
A retraction notice was published in J Pharmacol Exp Ther. PubMed does not show its stated reason, and we have not read it.
- Feb 22, 2024FilingsAthira 10-K describes the special committee’s findings on altered images and the dihexa patent
A company statement. See SEC filings above.
- Oct 21, 2021FilingsAthira 8-K says ATH-1017 turns into dihexa, and that dihexa development was discontinued
A company statement. See SEC filings above.
- Sep 2021LiteratureJournal publishes notices of concern on the 2013 and 2014 dihexa papers
Both are notices of concern, which a journal publishes while it looks into a paper.
- 2014LiteratureMechanism paper reports dihexa depends on the HGF/c-Met system
Later retracted. See above.
- 2013LiteraturePaper describes the design of dihexa
Carries a Sep 2021 notice of concern.
Still not covered
Left off rather than guessed:
- Policy coverage: HHS’s list of covered peptides sits in a policy attachment we could not open. That dihexa is outside it comes from two law-firm summaries, not from the document itself.
- FDA review: We found no FDA briefing document or advisory committee evaluation for dihexa. FDA’s notice for the July meeting does not name it, so the safety-risk page entry is the only FDA statement on it that we read.
- Patents: not researched for this dossier.
- Seller claims and independent lab reports: how it is marketed versus what testing finds. We have not collected testing data.
- Retraction and concern notices: we did not read them, so their stated reasons are not given here.
- Related trials: we did not review the clinical trials of ATH-1017 (fosgonimeton), which the company says turns into dihexa.
- WSU review: we did not look for its outcome.
- Unread items: full text of every paper; WADA lists for years other than 2022 and 2026; EU and other non-US trial registries.
- Warning letter and SEC completeness: web searches only.