History

Dihexa was developed by Joseph W. Harding and John W. Wright at Washington State University and carried the development code PNB-0408. It was commercialized through M3 Biotechnology, later renamed Athira Pharma. The compound is derived from angiotensin IV (Ang IV), building on a broader hypothesis linking the Ang IV / hepatocyte growth factor pathway to cognition. In April 2025, the group's key mechanism paper (Benoist et al. 2014) was retracted after a WSU investigation found falsified data; the journal had already issued an Expression of Concern in September 2021.

Dihexa is a small angiotensin IV-derived peptide that drew attention for animal data on dendritic spine growth and learning, plus an eye-catching claim that it is many orders of magnitude more potent than BDNF. It is sold online as a nootropic, but the honest picture is far more cautious than the marketing: there are no human trials of dihexa, the foundational mechanism paper behind it was retracted in 2025, and the related clinical compound failed its pivotal Alzheimer’s trial. This profile lays out what dihexa is, what is claimed, and what the evidence actually supports.

What it is

Dihexa (developmental code PNB-0408, chemical name N-hexanoic-Tyr-Ile-(6)-aminohexanoic amide, molecular formula C27H44N4O5, MW about 504.7, CAS 1401708-83-5) is a synthetic oligopeptide derived from angiotensin IV. It was modified at the N- and C-termini to increase lipophilicity, oral bioavailability, metabolic stability, and blood-brain-barrier penetration relative to the parent peptide. It was developed by Joseph W. Harding and John W. Wright at Washington State University and commercialized through M3 Biotechnology, later renamed Athira Pharma.

The proposed mechanism is that dihexa binds hepatocyte growth factor (HGF) with high affinity and potentiates signaling at the c-Met receptor, which in turn drives dendritic spinogenesis and synaptogenesis (the growth of new synaptic connections) in hippocampal neurons. As detailed below, the paper that established this HGF/c-Met binding mechanism has since been retracted, so it should be read as “claimed in now-retracted work,” not as an established fact.

The claims

Dihexa is promoted as a powerful nootropic and cognitive enhancer, built largely on one headline assertion: that it is roughly seven orders of magnitude more potent than BDNF (brain-derived neurotrophic factor) in a neurotrophic assay. That figure traces to the original WSU work and is best understood as a claim from that group, not as an independently established fact. The associated story is that dihexa’s tight binding to HGF and potentiation of c-Met signaling boosts synapse formation. Anecdotal user reports online describe improved focus and memory.

It is important to separate the compound’s plausible biology from the strength of the evidence behind these specific numbers, because the headline mechanistic claim rests substantially on work that has been formally retracted.

What the evidence actually shows

No human data exist. There are no published pharmacokinetic, toxicology, or efficacy trials of dihexa in humans. There are no registered or completed human clinical trials of dihexa itself. The anecdotal nootropic reports are uncontrolled and unverifiable.

The animal/cell evidence is real but limited, and the mechanistic anchor is retracted. The most-cited supportive study is McCoy et al. 2013 (Journal of Pharmacology and Experimental Therapeutics, PMID 23055539), in which oral dihexa reversed scopolamine-induced learning deficits, improved spatial learning in aged rats, and increased hippocampal spine density. That paper is real and has not been retracted.

However, the mechanistic anchor paper from the same group was retracted in 2025:

Benoist et al. 2014 (JPET), the paper establishing HGF/c-Met dependence, was retracted (notice published April 2025) after a WSU investigation found falsified data. The journal had already issued an Expression of Concern in September 2021, before the full retraction.

The net effect is that the mechanistic story is more compromised than it appears in older write-ups. The broader angiotensin-IV / HGF / cognition hypothesis predates the paper, but the specific HGF/c-Met dependence claim should not be cited as established evidence, and the retracted Benoist work must not be cited as support.

The related clinical compound is a different molecule, and it failed. The compound that actually reached clinical trials is fosgonimeton (ATH-1017, originally NDX-1017), best described as a prodrug of the dihexa-related active moiety rather than dihexa itself, advanced by Athira. Fosgonimeton failed its pivotal Phase 2/3 LIFT-AD trial (NCT04488419, roughly 315 participants randomized to 40 mg versus placebo for 26 weeks, subcutaneous). Announced in September 2024 and presented at CTAD in October 2024, it missed its primary endpoint (GST change -0.08, P=0.70) and key secondary endpoints, while being generally well tolerated, with some APOE ε4 subgroup and biomarker signals. Fosgonimeton is not dihexa and is itself unapproved. This is the closest thing to a human test of the underlying scaffold, and it did not work.

Legal and regulatory status

Dihexa itself is research-grade only. It has no FDA approval and no marketed product, and all dihexa-specific data are rodent and cell-culture. It is sold gray-market as a “research chemical” or nootropic and has no lawful dietary-supplement status.

Its compounding status is genuinely in flux. “Dihexa Acetate” had been on the FDA’s 503A interim bulks list, Category 2. In a 2026 FDA update (reported around April 2026), Dihexa Acetate was among 12 peptides removed from Category 2 and referred to Pharmacy Compounding Advisory Committee (PCAC) review, with PCAC consideration targeted before February 2027. Removal from Category 2 does not equal approval or Category 1 status, and does not by itself make the substance eligible for 503A compounding. Treat this as reported-but-provisional.

For athletes, dihexa is not individually named on the WADA Prohibited List, but as a pharmacologically active substance not approved by any government health authority for human use, it falls under category S0 (Non-Approved Substances), which is prohibited at all times, both in and out of competition. The S0 definition (drugs in pre-clinical or clinical development, plus designer, discontinued, and veterinary drugs) clearly captures it. One could also argue secondary relevance under the growth-factor provisions given its proposed mechanism, but S0 is the clear basis.

Safety

Human safety is unknown. There are no toxicology or pharmacokinetic data in humans. Vendor “anecdotal side-effect percentages” and specific rodent hepatotoxicity thresholds do not trace to a verifiable primary source and should be treated as unsubstantiated.

The principal theoretical risk is mechanistic. The HGF/c-Met pathway is a well-established oncogenic driver, so a compound designed to potentiate c-Met signaling carries a plausible tumor-promotion concern. No carcinogenicity studies in any species are published for dihexa. Early developer statements of “no apparent toxicity” came from short-duration preclinical work by a group whose related publication was later retracted, so they carry limited weight.

Bottom line

Dihexa is an interesting research molecule, not a proven cognitive enhancer. The evidence is thin and partly compromised: no human data at all, a retracted foundational mechanism paper, a failed pivotal trial for the related clinical prodrug, and an unquantified cancer-mechanism concern from its very target. The often-repeated “seven orders of magnitude more potent than BDNF” claim traces to the original WSU work and has never been tested in people. Anyone framing dihexa as a safe, effective nootropic is overstating the record. This is not medical advice.

Evidence grade: Animal only.