Dihexa
A potent angiotensin IV analog studied for cognitive enhancement. Its Dihexa-derived prodrug fosgonimeton failed its Phase 2/3 Alzheimer's trial (LIFT-AD, 2024), and the foundational 2014 HGF/c-Met mechanism paper was retracted in 2025 — material context that reshapes how the preclinical literature should be read.
What is Dihexa?
Dihexa is a synthetic peptide analog of angiotensin IV that was developed at Washington State University. It has shown remarkable potency in animal models of cognitive enhancement — reported to be approximately 10 million times more potent than BDNF at promoting new neural connections. However, it remains in very early stages of research with no human clinical trials.
What Dihexa Is Investigated For
Dihexa is investigated almost entirely for cognitive enhancement, memory improvement, and potential application in neurodegenerative disease, based on its role as a positive allosteric modulator of HGF/c-Met signaling and downstream synaptogenesis. The strongest evidence is preclinical — rodent studies from the Harding lab at Washington State University showing cognitive restoration at low doses, plus striking in vitro potency on dendritic spine formation — but not a single human clinical trial of any phase has been published after roughly 15 years. The honest caveats are substantial: the preclinical work comes largely from a single research program with sparse independent replication, the 'more potent than BDNF' figure refers specifically to an in vitro synaptogenesis assay rather than clinical efficacy, and the HGF/c-Met mechanism is the explicit target of approved oncology drugs designed to inhibit it — meaning long-duration carcinogenicity studies are absent and the cancer-promotion concern is mechanistic rather than hypothetical. Dihexa exists in the published literature as a preclinical research tool and in the marketplace as an unregulated research chemical.
History & Discovery
Dihexa was developed in the laboratory of Joseph Harding at Washington State University in the late 2000s and early 2010s as part of a long-running program designing metabolically stabilized analogues of angiotensin IV (AngIV). Harding's group had earlier shown that AngIV — a naturally occurring breakdown product of angiotensin II — appeared to enhance memory and learning in rodent models, but its short biological half-life made it impractical as a candidate molecule. Dihexa (formally N-hexanoic-Tyr-Ile-(6) aminohexanoic amide) is a hexapeptide-derived molecule that retained the procognitive activity of AngIV while resisting enzymatic degradation, and — unusually for a peptide — appearing to cross both the gut and the blood-brain barrier in animal studies. The most quoted finding from this program is that Dihexa potentiates hepatocyte growth factor (HGF) signaling at the c-Met receptor and drives dendritic spine and synaptogenesis in cell culture at extremely low concentrations, with reports comparing it to BDNF on a molar basis. Subsequent independent work has been thinner. The compound has not been advanced into formal IND-enabling studies or human clinical trials by Harding's group or any pharmaceutical sponsor. Outside academia, Dihexa diffused into the nootropic research-chemical market in the mid-2010s on the strength of those preclinical reports, well ahead of any regulatory or clinical evaluation in humans. Two developments since 2024 have materially reshaped how this body of work should be read. First, Athira Pharma — the corporate successor carrying the Dihexa-derived clinical program (Leen Kawas, formerly of the Harding lab, was CEO) — reported in September 2024 that its Phase 2/3 LIFT-AD trial of fosgonimeton (an oral Dihexa prodrug) in mild-to-moderate Alzheimer's disease missed its primary endpoint, with effectively no separation from placebo. This is the single most clinically relevant data point on the Dihexa pharmacophore and it is negative. Second, in January 2025 Athira paid a roughly $4 million False Claims Act settlement to resolve allegations that it failed to disclose Kawas's suspected image manipulation in NIH grant applications, and in April 2025 the foundational 2014 Benoist et al. paper in JPET — which established Dihexa's HGF/c-Met mechanism — was formally retracted amid the broader WSU misconduct investigation. The mechanism still has partial support from other studies and from a 2025 independent behavioral replication at Rowan University (Martino et al., Neurotrauma Reports), but the seminal paper is gone, the commercial development program failed in humans, and the provenance of some of the original preclinical signal is now disputed.
How It Works
Dihexa works by activating a receptor system (HGF/c-Met) that promotes the growth of new connections between brain cells. In animal studies, this has translated to improved memory and cognitive function, but human research has not been conducted.
Dihexa acts as an allosteric activator of hepatocyte growth factor (HGF) and its receptor c-Met. This pathway promotes dendritic spine formation, synaptogenesis, and neuronal survival. It also interacts with the AT4 receptor (insulin-regulated aminopeptidase). In animal models of cognitive impairment, it has demonstrated restoration of cognitive function at very low doses.
Evidence Snapshot
Human Clinical Evidence
None directly on Dihexa itself. The closest clinically relevant data is for fosgonimeton (ATH-1017), an oral prodrug of the Dihexa pharmacophore developed by Athira Pharma — its Phase 2/3 LIFT-AD trial in mild-to-moderate Alzheimer's missed its primary endpoint in September 2024, the most negative human-adjacent data point on this chemotype to date.
Animal / Preclinical
Moderate. Impressive animal data historically dominated by a single research group at Washington State University. A first independent behavioral replication emerged in 2025 (Martino et al., Rowan University — Dihexa rescued working-memory deficits after repeated mild TBI in rats, effect blocked by an HGF/MET-dimerization antagonist), though the seminal 2014 mechanism paper has since been retracted, so the mechanistic framing is weaker than it was.
Mechanistic Rationale
Moderate. HGF/c-Met pathway is well characterized, but Dihexa's specific interactions need more study.
Research Gaps & Open Questions
What the current literature has not yet settled about Dihexa:
- 01Any human clinical trial — not a single published study has tested Dihexa in humans for safety, pharmacokinetics, dose-response, or efficacy.
- 02Independent preclinical replication — most of the procognitive and synaptogenic findings come from a single research program at Washington State University, and the 2025 retraction of the foundational Benoist et al. 2014 JPET paper weakened the mechanistic literature. A 2025 independent behavioral replication by Martino et al. at Rowan University partially addresses this gap, but broader independent reproduction across labs remains sparse.
- 03Long-term oncology safety — given HGF/c-Met activation, formal carcinogenicity studies and long-duration tumor-promotion studies in genetically susceptible animal models are absent.
- 04Pharmacokinetics in humans — oral bioavailability is claimed from rodent work, but human absorption, distribution, metabolism, and excretion have never been characterized.
- 05Mechanism specificity — whether the cognitive effects observed in animals are driven primarily by HGF/c-Met potentiation, by AT4/IRAP interactions, or by a combination of pathways is not fully resolved.
- 06Real-world product quality — the research-chemical market lacks the analytical certificates of authenticity, third-party purity testing, and supply-chain traceability that would allow even informed users to know what they are taking.
Forms & Administration
Dihexa has been studied in animal models via various routes. No established human protocols exist. This is a research compound.
Dosing & Protocols
The ranges below reflect protocols commonly discussed in the literature and by clinicians — not a prescription. Actual dosing for any individual should be determined by a qualified healthcare provider who knows the patient.
Typical Range
There is no established human dose. Forum-described research-chemical protocols typically cite 8–45 mg per day taken orally, often based on the animal-to-human surface-area conversions of doses used in rat memory studies (~1.25 mg/kg by oral gavage in some Harding-lab protocols). These numbers are extrapolations, not derived from any human dose-finding work.
Frequency
Forum protocols most commonly describe once-daily oral dosing in the morning, sometimes split twice daily. There is no pharmacokinetic basis in humans for choosing one over the other; the choice reflects convenience and tolerability rather than data.
Timing Considerations
No specific timing requirements: can be administered at any time of day, with or without food, and is not tied to exercise timing. Consistency matters more than the specific clock — dose at roughly the same time each day (or same day each week, for weekly protocols) to keep exposure steady.
Cycle Length
No human cycle data exists. Forum descriptions span anything from 2–4 week courses tied to a specific cognitive task or study window, to multi-month continuous use. The longer end has no safety basis whatsoever.
Protocol Notes
Dihexa is unusual among peptides discussed in nootropic contexts in that animal studies suggest meaningful oral bioavailability, which is why it is typically described in oral capsule or sublingual form rather than as an injection. In practical research-chemical sourcing, purity varies substantially and the molecule is sometimes substituted or cut. There is no pharmaceutical-grade Dihexa and no FDA-recognized supplier. The distance between 'demonstrated activity at low concentrations in cultured neurons' and 'a safe and effective oral dose in a human brain' is enormous. Dihexa's animal data is genuinely interesting on its own terms, but extrapolating dose, schedule, or expected effect from rodent memory tasks to human cognition is speculative.
Dihexa is not approved for any medical use in any jurisdiction and has never been tested in humans in a published clinical trial. Any dose figure cited online is an extrapolation, not a prescription. The cancer-promotion concern (HGF/c-Met activation) is not theoretical in oncology pharmacology — it is the explicit target of multiple approved cancer drugs that work in the opposite direction.
Timeline of Effects
Onset
No human onset data exists. Animal studies of acute cognitive effects typically assess behavior within hours to a day after dosing, but how this translates to subjective effect in humans is unknown. Anecdotal reports describe perceived cognitive change within days to a few weeks of starting daily oral use, with substantial variability.
Peak Effect
No human peak-effect data exists. Animal cognitive-restoration studies typically run dosing over 5–14 days before testing, suggesting that cumulative effects may matter more than a single-dose peak, but this is inference from preclinical design, not characterization of human pharmacodynamics.
After Discontinuation
No data. Whether any cognitive effect would persist, fade quickly, or rebound after stopping Dihexa in humans has not been studied. The mechanistic basis (synaptogenesis-promoting effects on dendritic spines) is consistent with effects that could outlast clearance of the molecule, but this is theoretical.
Common Questions
Who Dihexa Is NOT For
- •Active or recent-history cancer — Dihexa is described as a positive allosteric modulator of HGF/c-Met signaling, a pathway that drives proliferation, motility, and metastasis in many tumor types and that is the explicit target of approved oncology drugs designed to inhibit it. Concurrent use in patients with known malignancy is mechanistically contraindicated.
- •Pregnancy — no human pregnancy data and no formal reproductive-toxicology studies in animals at doses relevant to human exposure.
- •Breastfeeding — no data on transfer into milk or on infant exposure.
- •Pediatric use — no studies in pediatric populations; Dihexa's effects on a developing nervous system are unknown and the rationale for use in children is absent.
- •Known or suspected predisposition to proliferative disease (e.g., personal or strong family history of HGF-driven cancers, hereditary cancer syndromes) — same mechanistic concern as active malignancy.
- •Concurrent use of HGF/c-Met-targeted oncology therapy (capmatinib, tepotinib, crizotinib, savolitinib) — Dihexa would oppose the pharmacologic intent of these drugs.
Drug & Supplement Interactions
There are no published clinical drug-interaction studies for Dihexa in humans. What follows is mechanistic inference, not documented interaction data. The most concrete concern is with HGF/c-Met-targeted cancer drugs (capmatinib, tepotinib, crizotinib and other multi-kinase inhibitors with c-Met activity). Dihexa is described as enhancing HGF/c-Met signaling; these drugs are designed to suppress it. Co-administration would be expected to undermine the oncology treatment. Because Dihexa is derived from angiotensin IV, theoretical interactions with the renin-angiotensin system have been raised — including with ACE inhibitors, ARBs, and direct renin inhibitors. The clinical magnitude of any such interaction at typical 'nootropic' research-chemical doses is unknown and probably small, but it has not been studied. Patients on cardiovascular medications should disclose any use to their prescriber. No interaction data exists for combinations with stimulants, SSRIs, other nootropics, anticoagulants, or hormonal therapies. Absence of documented interaction is not absence of interaction; it is absence of investigation.
Safety Profile
Common Side Effects
Cautions
- • No human clinical trials
- • Theoretical concerns about promoting growth in neural tissue
- • Very early-stage research compound
- • Not appropriate for casual use
What We Don't Know
Essentially everything about human safety, dosing, and long-term effects is unknown. This is a research compound, not a therapy.
Legal Status
United States
Dihexa is not FDA-approved for any indication. It has never been the subject of a published human clinical trial. It is not a controlled substance, but it is also not a recognized dietary supplement ingredient under DSHEA, not a legal cosmetic ingredient, and not legitimately available as a compounded medication. It is sold only through research-chemical channels, where the labeling typically specifies 'not for human consumption' — language that reflects regulatory reality rather than seller intent.
International
Dihexa is not approved as a medicine by EMA, MHRA, TGA, Health Canada, or any other major regulatory authority. Importation and sale through research-chemical channels is restricted or prohibited in several jurisdictions, including Australia where the TGA has taken enforcement action against unapproved peptide and peptide-analog products.
Sports & Competition
Dihexa is not currently named on the WADA Prohibited List. However, WADA's S0 category prohibits any substance 'not currently approved by any governmental regulatory health authority for human therapeutic use,' a description that fits Dihexa squarely. Athletes subject to WADA, USADA, or equivalent bodies should treat it as prohibited.
Regulatory status changes over time. Verify current local rules with a qualified professional.
Myths & Misconceptions
Myth
Dihexa is '10 million times more potent than BDNF,' so it must be dramatically more effective for cognition in humans.
Reality
That comparison comes from a specific in vitro synaptogenesis assay measuring dendritic spine formation in cultured neurons. It describes potency at a cellular endpoint, not clinical efficacy in a human brain. No human study has measured Dihexa's effect on cognition. The headline number is true within its narrow context and meaningless as a translational claim.
Myth
Because Dihexa is orally bioavailable, it is safe to take like a supplement.
Reality
Oral bioavailability is a pharmacokinetic property, not a safety property. Dihexa has never been tested in humans for safety at any dose; it is not a supplement; and its mechanism (HGF/c-Met enhancement) raises a serious mechanistic cancer-risk concern that has not been studied in long-duration animal carcinogenicity assays.
Myth
Dihexa is 'AngIV with the safety profile of AngIV,' so it inherits decades of cardiovascular peptide safety data.
Reality
Dihexa is a chemically modified analogue, not native angiotensin IV. The modifications that give it metabolic stability and oral bioavailability also change its biodistribution and persistence. Safety data on endogenous AngIV at picomolar physiologic concentrations does not transfer to chronic exogenous Dihexa exposure at milligram oral doses.
Myth
Research-chemical Dihexa is the same molecule that the Harding lab studies.
Reality
Research-chemical-channel product varies in purity, identity, and concentration. There is no pharmaceutical-grade Dihexa and no chain-of-custody verification between an academic synthesis batch and what is sold online. Even buyers who trust the seller cannot verify they are receiving the same compound described in the published animal studies.
Myth
Dihexa is FDA-approved or in clinical trials.
Reality
It is neither. There has never been a published Phase I, II, or III trial of Dihexa itself in humans. The closest human data is for Athira's fosgonimeton (ATH-1017), an oral prodrug built on the Dihexa pharmacophore, which missed its primary endpoint in the Phase 2/3 LIFT-AD Alzheimer's trial in September 2024.
Myth
Dihexa's HGF/c-Met mechanism is rock-solid — it has been established for a decade.
Reality
The foundational 2014 Benoist et al. JPET paper that first established the HGF/c-Met mechanism was formally retracted in April 2025 following a Washington State University research-misconduct investigation, and the corporate successor Athira paid a $4M False Claims Act settlement in January 2025 tied to undisclosed image-manipulation concerns in grant applications. The mechanism still has partial support from later studies and from a 2025 independent behavioral replication at Rowan University, but the provenance of the seminal evidence is now materially contested.
Published Research
9 studiesRetraction: The Procognitive and Synaptogenic Effects of AngIV-Derived Peptides Are Dependent on Activation of the HGF/c-Met System (Benoist et al., 2014)
Formal April 2025 retraction of the foundational 2014 J Pharmacol Exp Ther paper that established Dihexa's HGF/c-Met mechanism, following a Washington State University research-misconduct investigation involving image-manipulation concerns.
AngIV-Analog Dihexa Rescues Cognitive Impairment and Recovers Memory in the APP/PS1 Mouse via the PI3K/AKT Signaling Pathway
Stem cell, Granulocyte-Colony Stimulating Factor and/or Dihexa to promote limb function recovery in a rat sciatic nerve damage-repair model: Experimental animal studies
Contributions by the Brain Renin-Angiotensin System to Memory, Cognition, and Alzheimer's Disease
Connecting the brain cholesterol and renin-angiotensin systems: potential role of statins and RAS-modifying medications in dementia
Evaluation of Metabolically Stabilized Angiotensin IV Analogs as Procognitive/Antidementia Agents
Dihexa Rescues Working-Memory Deficits After Repeated Mild Traumatic Brain Injury via HGF/MET Signaling in Rats (Martino et al., 2025)
First published independent behavioral replication of Dihexa's procognitive effects from a research group (Rowan University) outside the original Harding lab — Dihexa rescued working memory after repeated mild TBI, and the effect was blocked by the HGF/MET-dimerization antagonist Hinge.
Athira Pharma Phase 2/3 LIFT-AD Trial of Fosgonimeton Fails Primary Endpoint in Mild-to-Moderate Alzheimer's Disease (September 2024)
Athira's lead clinical candidate fosgonimeton (ATH-1017), an oral prodrug of the Dihexa pharmacophore, missed its primary endpoint in mild-to-moderate Alzheimer's disease — the most clinically relevant negative data point on this chemotype to date.
Athira Pharma $4 Million False Claims Act Settlement (January 2025)
Athira Pharma paid ~$4.07M to resolve DOJ False Claims Act allegations that it failed to disclose former CEO Leen Kawas's suspected image-manipulation in NIH grant applications — extending the WSU misconduct findings into commercial development.
Quick Facts
- Class
- Angiotensin Analog
- Tier
- D
- Evidence
- Preliminary
- Safety
- Limited Data
- Updated
- Apr 2026
- Citations
- 9PubMed
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View Clinical TrialsLinks to ClinicalTrials.gov for reference. Listing does not imply endorsement.