Dihexa: why a 'stronger-than-BDNF' compound worries researchers

Where 'millions of times stronger than BDNF' comes from

Dihexa is usually sold with one number: that it is seven orders of magnitude, or ten million times, more potent than BDNF, the brain's best-known growth factor for nerve connections. The figure circulates on seller pages and nootropic forums. It does not appear in the abstract of the 2013 paper that introduced dihexa, which describes 'marked synaptogenic activity' and memory improvements in rats without a BDNF comparison ¹.

Even taken at face value, a potency number from a cell assay says how little of a compound it takes to trigger an effect in a dish. It says nothing about whether the effect helps a person, how long it lasts, or what else the compound does. A compound can be extraordinarily potent in a dish and useless or harmful in a body. Evidence grade for any cognitive benefit in people: none, because no human study exists.

What dihexa is

Dihexa comes from a long line of research on angiotensin IV, a fragment of the hormone system that controls blood pressure, which had shown memory effects in rodents. A 2018 systematic review of animal studies found that angiotensin IV and a related peptide improved learning and memory across many experiments, while noting the evidence came from animals ². The trouble was that angiotensin IV breaks down quickly and does not reach the brain when swallowed.

In 2013 a Washington State University group including Jay Wright and Joseph Harding reported that the activity of one angiotensin IV analogue lived in its first three amino acids. By capping that fragment at both ends they made N-hexanoic-Tyr-Ile-(6) aminohexanoic amide, which they named dihexa: stable, active by mouth and able to cross into the brain in rats, where it reversed memory deficits caused by the drug scopolamine and in aged rats ¹. It is a modified peptide, which our encyclopedia classes as a peptidomimetic ³.

What the animal studies show

Outside the original laboratory, a handful of groups have tested dihexa. In mice engineered to develop Alzheimer's-like pathology, oral dihexa restored performance in a water maze and increased neurons and the synapse protein synaptophysin, through PI3K/AKT signalling (animal evidence) ⁴. In zebrafish larvae, it protected the sensory hair cells of the lateral line from aminoglycoside antibiotics, an effect blocked by an HGF antagonist (animal evidence; this study included members of the original group) ⁵. In rats with repeated mild head injuries, an HGF/MET-positive modulator, which the authors index under the keyword dihexa, rescued working memory in a dose-dependent way (animal evidence) ⁶.

Not everything worked. In 40 rats given a mitochondrial toxin that mimics Huntington's disease, dihexa (tested under its code PNB-0408) did not protect against weight loss, motor problems or memory deficits (animal evidence) ⁷. Our dihexa entry also records a rat nerve-repair study ³. That is the whole evidence base: a small number of rodent and fish studies, several from one group, none in people.

The papers that were retracted

Dihexa's story was that it works by binding hepatocyte growth factor (HGF) and helping it switch on its receptor, c-Met, which in turn builds new nerve connections. That mechanism rested on a 2014 paper reporting that dihexa bound HGF with high affinity, boosted c-Met activation and lost its memory effect in rats when HGF was blocked ⁸. PubMed now records that paper as retracted, with a retraction notice published in April 2025 ⁹. Two earlier papers from the same group, from 2011 and 2012, which developed the idea of angiotensin IV analogues as HGF/Met modifiers, are also recorded as retracted ^{10 11}.

The 2013 paper that introduced dihexa is not retracted, but PubMed lists a 2021 expression of concern from the journal ¹. Our encyclopedia entry has flagged the retractions since they appeared ³. The practical meaning is that the published explanation for how dihexa works is no longer supported by the papers that made it. Independent work, such as the 2021 mouse study, suggests some biological activity, but the mechanism that sellers describe is not established.

Why c-Met worries cancer researchers

HGF and c-Met matter far beyond memory. c-Met, also written MET, is a proto-oncogene: a normal gene that, when overactive, helps cells grow, move and invade. A 2021 review in Oncogene describes hyperactive HGF/c-MET signalling as a hallmark of many cancers, involved in tumour growth, spread and resistance to treatment (review of cancer evidence) ¹². A 2025 review in Nature Reviews Clinical Oncology notes that MET alterations are associated with tumour development, invasion and metastasis across solid cancers, and that several MET-blocking drugs are approved for lung cancers driven by MET mutations ¹³.

That is the heart of the worry. Dihexa was promoted precisely as a compound that strengthens HGF/c-Met signalling. The cancer field spends enormous effort trying to switch that same signalling off. The retracted record holds an odd footnote: the same laboratory's 2011 paper, now retracted, described HGF-mimicking molecules that blocked Met and had anticancer activity ¹⁰.

To be precise: no study has shown that dihexa causes or accelerates cancer. No study has looked. There are no long-term toxicity studies in the published record, and no human exposure at all. The concern is theoretical but grounded in well-established biology, and it would weigh most for anyone with a current or past cancer, a precancerous condition or a strong family history. Evidence grade for cancer risk: unknown, untested.

The closest human test, and how it went

The compound that reached large human trials was not dihexa but fosgonimeton, a different small molecule developed by Athira Pharma, whose scientists describe it as a positive modulator of the HGF/MET system (company animal studies) ¹⁴. In a phase 1 trial in 88 people, daily injections were well tolerated across doses, with brain-wave changes suggesting it reached the brain ¹⁵.

The decisive test was LIFT-AD, a randomised, placebo-controlled phase 2/3 trial in mild-to-moderate Alzheimer's disease. In the 287-person primary analysis, fosgonimeton did not achieve its primary or secondary endpoints; the difference on the combined cognition and daily-function score was close to zero (p = 0.70). Serious adverse events were similar, but 14.2% stopped fosgonimeton because of side effects, mostly injection-site reactions, against 4.6% on placebo (human trial evidence) ¹⁶.

Fosgonimeton is not dihexa, and its failure does not prove dihexa would fail. But it is the only randomised human test of the idea that boosting HGF/MET signalling improves cognition, and on its main measures the answer was no.

Dihexa side effects: what is actually known

Nothing, from controlled research. There is no published study of dihexa in people, so there is no measured rate of any side effect, no known safe amount and no information on interactions with medicines. FDA's page on bulk drug substances that may present safety risks in compounding, current as of April 22, 2026, says the agency has not identified any human exposure data on dihexa acetate by any route and lacks the information to know whether it would cause harm ¹⁷.

Online reports of headaches, sleep changes or mood effects are anecdotes. They cannot establish frequency or cause, and they cannot detect slow effects such as cancer that would take years to appear. Products sold as dihexa are also unverified: without a certificate of analysis from an identifiable laboratory, there is no way to know what a capsule or vial contains.

Regulatory status, as of October 3, 2026

Dihexa is not approved by FDA or any other regulator we know of. FDA had placed dihexa acetate in Category 2, substances that may present significant safety risks in compounding, until the nomination was withdrawn in April 2026; it now sits in no category, which means pharmacies have no lawful basis to compound it ^{3 17}. FDA's Pharmacy Compounding Advisory Committee is due to discuss dihexa acetate, with four other substances, at a meeting before the end of February 2027; FDA's meeting page, current as of April 15, 2026, says the time and location will be scheduled ¹⁸. Our guide to the second PCAC five covers that meeting.

For athletes, dihexa is not named on WADA's Prohibited List, but as a substance with no approval for human use it falls under S0, non-approved substances, which are prohibited at all times ³.

Questions to ask before taking dihexa

• Has dihexa ever been tested in people? (As of October 3, 2026, no published study exists.)
• Do I, or does anyone in my family, have a history of cancer, and how would a compound that activates a cancer-linked pathway affect that?
• Which of the studies behind the product are still standing, and which were retracted or flagged?
• What exactly is in the product, and is there a certificate of analysis from an identifiable laboratory for this batch?
• Is there an approved treatment, or a better-studied option, for the problem I am trying to solve?

How dihexa compares with other 'brain peptides'

Other compounds sold for cognition have thin evidence too, but of a different kind. Semax and selank have small Russian clinical studies, and noopept has limited human data. Dihexa has none at all, and it adds a mechanism concern the others do not carry. Our semax and selank evidence review sets out what those human studies show.

The bottom line

Dihexa produced striking results in rats a decade ago, and a few independent animal studies suggest it does something in the brain. But the papers that explained how it works were retracted, the first paper carries an expression of concern, no human has taken it in a published study, and its advertised mechanism is a pathway that drives cancer growth when overactive. The closest drug to reach a large human trial failed. 'Stronger than BDNF' is a lab-dish number attached to a compound whose risks are simply unknown.

Frequently asked questions

Is dihexa really stronger than BDNF?

The 'seven orders of magnitude' figure circulates online but is not in the abstract of the paper that introduced dihexa. Any such comparison would come from cell assays, which measure how little compound triggers an effect in a dish, not benefit or safety in people.

What are the side effects of dihexa?

Unknown. No published study has given dihexa to people, so there is no measured side-effect rate. FDA says it has no human exposure data for dihexa acetate.

Does dihexa cause cancer?

No study has shown that it does, and none has looked. The concern is that dihexa was promoted as activating HGF/c-Met, a proto-oncogene pathway that drives tumour growth and spread when overactive.

Were the dihexa studies retracted?

PubMed records the 2014 paper that tied dihexa to HGF/c-Met as retracted in April 2025, along with 2011 and 2012 papers from the same group. The 2013 paper that introduced dihexa carries a 2021 expression of concern.

Is dihexa legal?

It is not approved anywhere we know of. As of October 3, 2026 it is in no FDA compounding category, FDA's compounding committee is due to review it by the end of February 2027, and WADA prohibits it under S0.

Related on Grey Peptides

• Dihexa
• The second PCAC five
• Semax and selank: the evidence

Sources

1. McCoy, A. T., et al. (2013). Evaluation of metabolically stabilized angiotensin IV analogs as procognitive/antidementia agents. J Pharmacol Exp Ther, 344(1), 141-54. PMID: 23055539
2. Ho, J. K., et al. (2018). Cognitive benefits of angiotensin IV and angiotensin-(1-7): A systematic review of experimental studies. Neurosci Biobehav Rev, 92, 209-225. PMID: 29733881
3. Grey Peptides encyclopedia entry for dihexa: molecule class (peptidomimetic), FDA and compounding status (503A Category 2 until the nomination was withdrawn in April 2026; no category since), WADA status (S0, inferred), retraction notes and study cards. Read October 3, 2026.
4. Sun, X., et al. (2021). AngIV-Analog Dihexa Rescues Cognitive Impairment and Recovers Memory in the APP/PS1 Mouse via the PI3K/AKT Signaling Pathway. Brain Sci, 11(11). PMID: 34827486
5. Uribe, P. M., et al. (2015). Hepatocyte growth factor mimetic protects lateral line hair cells from aminoglycoside exposure. Front Cell Neurosci, 9, 3. PMID: 25674052
6. Martino, K. A., et al. (2025). Hepatocyte Growth Factor/MET Activator Rescues Working Memory Deficits after Repeated Mild Traumatic Brain Injury. Neurotrauma Rep, 6(1), 991-998. PMID: 42825082
7. Wells, R. G., et al. (2024). Effects of an Angiotensin IV Analog on 3-Nitropropionic Acid-Induced Huntington's Disease-Like Symptoms in Rats. J Huntingtons Dis, 13(1), 55-66. PMID: 38489193
8. Benoist, C. C., et al. (2014). 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, 351(2), 390-402. RETRACTED (retraction notice April 2025); cited here as a retracted paper, not as evidence.
9. Benoist, C. C., et al. (2025). 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 351 (2014) 390-402]. J Pharmacol Exp Ther, 392(4), 103567. PMID: 40312093
10. Kawas, L. H., et al. (2011). Mimics of the dimerization domain of hepatocyte growth factor exhibit anti-Met and anticancer activity. J Pharmacol Exp Ther, 339, 509-18. RETRACTED according to PubMed (read October 3, 2026); cited here as a retracted paper, not as evidence.
11. Kawas, L. H., et al. (2012). Development of angiotensin IV analogs as hepatocyte growth factor/Met modifiers. J Pharmacol Exp Ther, 340, 539-48. RETRACTED according to PubMed (read October 3, 2026); cited here as a retracted paper, not as evidence.
12. Fu, J., et al. (2021). HGF/c-MET pathway in cancer: from molecular characterization to clinical evidence. Oncogene, 40(28), 4625-4651. PMID: 34145400
13. Lee, J. B., et al. (2025). Evolving roles of MET as a therapeutic target in NSCLC and beyond. Nat Rev Clin Oncol, 22(9), 640-666. PMID: 40681868
14. Johnston, J. L., et al. (2023). Fosgonimeton, a Novel Positive Modulator of the HGF/MET System, Promotes Neurotrophic and Procognitive Effects in Models of Dementia. Neurotherapeutics, 20(2), 431-451. PMID: 36538176
15. Hua, X., et al. (2022). Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of the Positive Modulator of HGF/MET, Fosgonimeton, in Healthy Volunteers and Subjects with Alzheimer's Disease: Randomized, Placebo-Controlled, Double-Blind, Phase I Clinical Trial. J Alzheimers Dis, 86(3), 1399-1413. PMID: 35180125
16. Porsteinsson, A. P., et al. (2025). Fosgonimeton in mild-to-moderate Alzheimer's disease. J Alzheimers Dis Rep, 9, 25424823251405817. PMID: 41393340
17. FDA. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (entry for dihexa acetate). Content current as of April 22, 2026; read October 1, 2026. FDA
18. FDA. Meeting of the Pharmacy Compounding Advisory Committee (February 2027): agenda including dihexa acetate; time and location 'will be scheduled in the coming months'. Content current as of April 15, 2026; read October 3, 2026. FDA

Educational information, not medical advice. Each dose in this guide names its source, an approved label or a published study. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose.