Dihexa: Nootropic Research, Mechanism & Safety

Dihexa is a small, peptide-derived analog of angiotensin IV that improved memory in rodent models and is proposed to work by enhancing hepatocyte growth factor (HGF) signaling through the c-Met receptor. All of its efficacy evidence is preclinical: there are no published human efficacy trials, and no published human safety data. The key mechanism paper was retracted in 2025, and because c-Met is a well-established oncogenic pathway, long-term safety is a genuine open question. Dihexa acetate is on the agenda for the FDA's second PCAC meeting, expected before the end of February 2027.

Educational content for licensed healthcare professionals. Not medical advice; dosing and treatment decisions belong to the prescribing clinician.

Dihexa at a Glance

What Is Dihexa?

Dihexa came out of a Washington State University program studying angiotensin IV, a fragment of the renin-angiotensin system with long-reported procognitive effects in animals. Native angiotensin IV and its analog Nle1-angiotensin IV break down quickly and do not cross the gut or blood-brain barrier well. The researchers trimmed the active core to a three-residue motif and modified both ends to improve stability and penetration, producing N-hexanoic-Tyr-Ile-(6) aminohexanoic amide, named dihexa [1].

Chemically, dihexa is best described as a small, peptide-derived molecule (a peptidomimetic) rather than a conventional peptide; its developers' reviews call it a small-molecule angiotensin IV analog [6]. It also appears in the literature as PNB-0408 [5]. Our library entry is at Dihexa, and our nootropic peptides guide places it among other cognitive compounds.

How It Is Proposed to Work

The developers proposed that dihexa works by binding hepatocyte growth factor and boosting signaling through its receptor, c-Met. HGF/c-Met signaling in the brain is linked to dendritic growth, synapse formation, and neuroprotection, and the group published reviews presenting it as a target for Alzheimer's disease [6].

The key mechanistic evidence has been retracted. The central paper reporting that dihexa binds HGF and that its procognitive effects depend on the HGF/c-Met system [3] received an expression of concern in 2021 and was retracted by the Journal of Pharmacology and Experimental Therapeutics in 2025 [4]. The 2013 paper that first described dihexa and its effects in rat memory models [1] also carries a 2021 expression of concern from the same journal [7]. Readers should treat the HGF/c-Met mechanism as a hypothesis whose primary support is compromised, not an established fact.

Independent work has explored other pathways. A 2021 study in APP/PS1 Alzheimer's model mice reported improved Morris water maze performance and reduced glial activation and inflammatory cytokines, and attributed the effects to PI3K/AKT signaling [2].

What the Research Shows

Every efficacy finding for dihexa is from animals or cells:

• Rat memory models. In the 2013 discovery paper, dihexa reversed scopolamine-induced deficits and improved performance in aged rats on spatial-learning tasks, and increased synapse formation in hippocampal cultures [1]. This paper is under an expression of concern [7].
• Alzheimer's model mice. In APP/PS1 mice, dihexa restored spatial learning in the water maze and reduced markers of neuroinflammation [2].
• Traumatic brain injury. A 2025 study in a mouse model of repeated mild traumatic brain injury reported that an HGF/MET positive modulator rescued working-memory deficits [8].
• A negative result. In a rat model of Huntington's-like neurotoxicity, dihexa (as PNB-0408) did not protect against motor or cognitive deficits [5].
• Systematic review. A 2018 systematic review of experimental studies found that angiotensin IV and its analogs, including dihexa, generally improved performance in animal models of cognitive deficit, with the most consistent effects when given directly into the brain near the time of learning [9].

There are no published human trials of dihexa for memory, cognition, or any neurological condition.

Safety: What Is Known and What Is Not

There are no published human safety data. That is the central safety fact, and the site's FDA peptide status tracker notes that dihexa was previously withdrawn from consideration for lack of human exposure data.

The c-Met concern. c-Met, the receptor dihexa is proposed to potentiate, is encoded by the MET proto-oncogene. When genetically altered or persistently activated, MET signaling can initiate and sustain tumor growth and promote invasion and metastasis, and it is the target of approved cancer therapies [10]. If dihexa does enhance HGF/c-Met signaling, long-term or high-exposure use raises a theoretical concern about promoting growth of existing or undiagnosed tumors. To be clear, there is no published evidence that dihexa causes cancer; the concern is mechanistic and unresolved because the relevant long-term studies have not been done. It is, however, a reason prescribers apply particular caution in patients with a history of cancer or elevated cancer risk.

Unknowns. Pharmacokinetics, drug interactions, effects in pregnancy, and effects of long-term use in humans have not been characterized. Products sold outside licensed pharmacies add identity and purity risk.

Regulatory Status in 2026

Dihexa is not FDA-approved for any use. Dihexa acetate is on the agenda for the second PCAC meeting, which FDA has announced for a date before the end of February 2027, alongside GHK-Cu, Cathelicidin LL-37, Melanotan II, and PEG-MGF. A PCAC vote is advisory; even a favorable vote would not place dihexa on the 503A Bulks List until FDA completes notice-and-comment rulemaking. For how the July 2026 meeting played out, see the July 2026 PCAC peptide votes. Current status is maintained on our FDA peptide status tracker.

Frequently Asked Questions

What is Dihexa?

Dihexa is a metabolically stabilized, peptide-derived analog of angiotensin IV, developed to cross the blood-brain barrier. It improved memory in rodent models, but it has never been tested for efficacy in published human trials.

Does Dihexa work in humans?

Not established. All efficacy data are from animals and cell cultures, and the central paper on its mechanism was retracted in 2025.

Is Dihexa safe?

Its safety in humans is unknown because no human safety data have been published. Because it is proposed to enhance c-Met, an oncogenic signaling pathway, long-term safety is a significant open question.

Is Dihexa a peptide?

It is peptide-derived. Dihexa is built on a modified two-amino-acid core (tyrosine and isoleucine) with chemical caps on both ends, and its developers describe it as a small-molecule angiotensin IV analog.

What dose of Dihexa is used?

This guide does not give one. No human dose has been established, and dosing is the prescribing clinician's decision.

Is Dihexa legal to compound?

It is not FDA-approved. Dihexa acetate is scheduled for review at the second PCAC meeting before the end of February 2027; check our FDA peptide status tracker for the current position.

References

1. McCoy AT, et al. Evaluation of metabolically stabilized angiotensin IV analogs as procognitive/antidementia agents. J Pharmacol Exp Ther. 2013;344(1):141-54. PubMed (Expression of concern issued 2021; see ref. 7.)
2. Sun X, et al. AngIV-analog dihexa rescues cognitive impairment and recovers memory in the APP/PS1 mouse via the PI3K/AKT signaling pathway. Brain Sci. 2021;11(11):1487. PubMed
3. Benoist CC, et al. The procognitive and synaptogenic effects of angiotensin IV-derived peptides are dependent on activation of the hepatocyte growth factor/c-met system. J Pharmacol Exp Ther. 2014;351(2):390-402. Retracted. PubMed
4. Benoist CC, et al. Retraction notice to "The procognitive and synaptogenic effects of angiotensin IV-derived peptides are dependent on activation of the hepatocyte growth factor/c-Met system." J Pharmacol Exp Ther. 2025;392(4):103567. PubMed
5. Wells RG, et al. Effects of an angiotensin IV analog on 3-nitropropionic acid-induced Huntington's disease-like symptoms in rats. J Huntingtons Dis. 2024;13(1):55-66. PubMed
6. Wright JW, Kawas LH, Harding JW. The development of small molecule angiotensin IV analogs to treat Alzheimer's and Parkinson's diseases. Prog Neurobiol. 2015;125:26-46. PubMed
7. Notice of Concern: McCoy AT, et al. (2013) Evaluation of metabolically stabilized angiotensin IV analogs as procognitive/antidementia agents. J Pharmacol Exp Ther. 2021;378(3):313. PubMed
8. Martino KA, et al. Hepatocyte growth factor/MET activator rescues working memory deficits after repeated mild traumatic brain injury. Neurotrauma Rep. 2025;6(1):991-998. PubMed
9. Ho JK, Nation DA. Cognitive benefits of angiotensin IV and angiotensin-(1-7): a systematic review of experimental studies. Neurosci Biobehav Rev. 2018;92:209-225. PubMed
10. Comoglio PM, Trusolino L, Boccaccio C. Known and novel roles of the MET oncogene in cancer: a coherent approach to targeted therapy. Nat Rev Cancer. 2018;18(6):341-358. PubMed

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