Dihexa: Evidence, Mechanism, Dosing & Legal Status

Dihexa (PNB-0408; N-hexanoic-Tyr-Ile-(6)-aminohexanoic amide) is a synthetic peptide derived from angiotensin IV, developed at Washington State University and promoted in nootropic and anti-aging circles as a potent cognitive enhancer.15 Its popularity rests on dramatic preclinical claims; its proof in humans is nonexistent, and a core part of its scientific foundation has collapsed. This monograph separates the two.

This article is informational and editorial content for research and educational purposes only. It is not medical advice, not a protocol to follow, and not a sourcing guide. Dihexa is not an FDA-approved drug; it is sold as a "research chemical not for human consumption" and is prohibited in sport. Dosing figures are reported strictly as seen in the published literature and anecdotal community reports for completeness — not as recommendations. Consult a licensed clinician before any health decision.

What is dihexa and how does it work?

Dihexa is an oligopeptide with the systematic name N-hexanoic-tyrosine-isoleucine-(6)-aminohexanoic amide, molecular formula C₂₇H₄₄N₄O₅ and molecular weight roughly 504.67 g/mol.15 Native angiotensin IV is rapidly degraded by peptidases and does not cross the blood-brain barrier; dihexa was engineered with N-terminal hexanoyl and C-terminal aminohexanoic-amide modifications to increase hydrophobicity, confer metabolic stability and enable brain penetration.4 It emerged from the angiotensin-IV cognition program of Joseph Harding and John Wright at Washington State University, which since the 1990s explored Ang IV analogs that reversed scopolamine-induced memory deficits in rats.3

The dominant published mechanism — all of it preclinical — is that dihexa binds hepatocyte growth factor (HGF) and acts as an allosteric potentiator or dimerization mimetic, augmenting HGF's ability to activate its receptor tyrosine kinase c-Met (MET) at otherwise subthreshold HGF concentrations. c-Met activation then engages downstream PI3K/AKT and MAPK/ERK cascades that drive neuronal survival, dendritic arborization and synapse formation.15 A critical caveat applies: the widely cited binding affinity (around 65 picomolar) and the central c-Met phosphorylation and synaptogenesis data derive from Benoist and colleagues 2014, which was formally retracted in April 2025 for falsified figures — so the quantitative mechanism and potency claims cannot be relied upon.12 An earlier, competing framework proposed Ang IV analogs act via IRAP (insulin-regulated aminopeptidase, the AT4 site); this debate was never definitively resolved.5 No formal human pharmacokinetic profile for dihexa exists; commonly repeated figures such as "38% oral bioavailability" appear only in secondary and vendor sources and are not anchored to a verifiable peer-reviewed study.3

What is the evidence by indication?

Every indication below is animal-model or cell-system evidence, graded C. There are no human efficacy data for dihexa itself, and the most-cited mechanistic study is retracted.2

The cognition signal is the most cited. In a scopolamine-amnesia model and in aged Sprague-Dawley rats, oral dihexa reversed spatial-learning deficits, with brain levels reported sufficient for a therapeutic effect after oral dosing; notably, dihexa did not improve cognition in animals with normal baseline cognition, so the effect was deficit-specific.3 In APP/PS1 transgenic Alzheimer's mice, intragastric dihexa over roughly three months was reported to restore declining brain Ang IV, preserve cognition, reduce neuronal loss and dampen neuroinflammation.6 The now-retracted Benoist 2014 study reported that dihexa increased dendritic spine density on hippocampal neurons and that oral dihexa reversed scopolamine deficits via a central HGF/c-Met-dependent mechanism — findings that are retracted and should not be cited as established.12

The one rigorous human test of the underlying HGF/MET-cognition thesis came through a separate prodrug. Dihexa itself never entered clinical trials; M3 Biotechnology, later Athira Pharma, developed fosgonimeton (ATH-1017), a subcutaneously injected molecule rapidly cleaved in plasma to a dihexa-related active metabolite.9 In Phase 1 (NCT03298672, 88 subjects) it was generally safe and well tolerated, with mainly injection-site pain and pruritus.7 But the Phase 2/3 LIFT-AD trial in roughly 315 patients with mild-to-moderate Alzheimer's failed its primary endpoint (Global Statistical Test; -0.08, P=0.70) and key secondaries, with only numerical, non-significant trends favoring treatment.8

What doses appear in the literature?

Reported strictly as information, not a protocol. Dihexa has no approved human use and no validated human dose.6 In preclinical rodent work, oral dosing was around 2 mg/kg in rats (scopolamine and aged-rat cognition studies) and 1.44 to 2.88 mg/kg intragastric in APP/PS1 mice over weeks to months.3 In-vitro synaptogenic activity was reported at picomolar concentrations, but this comes from the retracted study and is not reliable.1 Anecdotal human use — with no clinical basis — describes roughly 5 to 50 mg per day taken orally or applied transdermally, often dissolved in a carrier such as DMSO and sometimes cycled; these reports are unvalidated, unsupervised, and carry unknown bioavailability and safety.6 For context, the clinical prodrug fosgonimeton was dosed at 40 mg once-daily subcutaneously in LIFT-AD — a different molecule, not dihexa.8 Dihexa is poorly water-soluble by design, which is itself a practical liability and one reason a water-soluble prodrug was developed.9

How safe is dihexa?

Human safety of dihexa itself is essentially unknown; no completed human trials of dihexa exist and there are no long-term human safety data.6 The dominant theoretical risk is mechanistic and serious: c-Met is a well-characterized oncogene, and HGF/c-Met signaling drives tumor growth, invasion, metastasis and angiogenesis. A systemic agent that potentiates this pathway raises a credible cancer-promotion concern, especially with chronic, unsupervised dosing — a risk repeatedly flagged by the Alzheimer's Drug Discovery Foundation.6 Short-duration animal studies were reported to show no apparent toxicity, but these are brief, animal-only, and partly drawn from the same compromised research program.15 Theoretical contraindications include active, prior or strong family-history cancer, uncharacterized precancerous lesions, and pregnancy or breastfeeding given the absence of reproductive data. For the prodrug, human adverse events were mainly mild injection-site reactions with occasional transient eosinophil rises.7 The research-integrity problem compounds the safety picture: because the foundational binding-affinity and mechanism data were falsified and retracted, any effective-dose and safety-margin extrapolations built on them are unreliable.2

What is the FDA and WADA status in 2026?

Dihexa is not an FDA-approved drug; there is no NDA or BLA, and it is sold only as a research chemical labeled not for human consumption.6 Dihexa acetate was moved into 503A Category 2 (significant safety concerns, not permitted in compounding) in September 2023, and it was never in Category 1, so it has never been legally usable in 503A compounding.10 Under the January 7, 2025 final interim guidance, the FDA stopped placing newly nominated substances into Categories 2 and 3.12 In April 2026 the FDA announced it would remove dihexa acetate from Category 2 within seven calendar days and convene a second Pharmacy Compounding Advisory Committee (PCAC) meeting before the end of February 2027 to review it alongside GHK-Cu, Melanotan II, LL-37 and PEG-MGF.11 The critical legal point: removal from Category 2 is not approval, the PCAC recommendation is non-binding, formal notice-and-comment rulemaking would still be required, and dihexa remains not legally compoundable as of mid-2026.11

For athletes the picture is unambiguous. As a non-approved pharmacological substance, dihexa is prohibited at all times under WADA category S0 (non-approved substances) on the 2026 Prohibited List that came into force on January 1, 2026; its HGF and growth-factor mechanism also falls within the spirit of the S2 growth-factor prohibitions.13 It is not currently listed explicitly by name, but S0 captures it regardless of naming, and no Therapeutic Use Exemption is available for a substance with no approved medical use.14 Dihexa is not a DEA-controlled substance.

Bottom line. Dihexa pairs genuinely striking rodent memory-rescue signals with a near-total absence of human proof and a foundation partly destroyed by research fraud. From a functional, root-cause standpoint, supporting synaptic health through validated levers — metabolic health, sleep, exercise, omega-3s and cognitive engagement — is far better evidenced than an unapproved, fraud-tainted, untested-in-humans research chemical that activates an oncogenic pathway. Graded C, legally unsettled, and banned in sport. Regulatory facts here are current as of June 2026; the PCAC review (before February 2027) was pending at the time of writing and should be re-verified after that date.