- 01Potent in a dish vs effective in people
Dihexa's famous 'ten million times stronger than BDNF' figure measures spine growth in cultured rat neurons, and the paper explaining its mechanism is retracted. The only human test of the same HGF/MET idea, the sibling drug fosgonimeton, missed its main goal in two Alzheimer's trials.
Dihexa is a lab-made fragment of angiotensin, a hormone better known for controlling blood pressure, developed at Washington State University as a possible dementia drug and tested in rats. Every result behind its online reputation comes from rat brains and dishes of rat neurons, almost all of it from one research group. The paper that explained how dihexa works was retracted in 2025 2, and the original dihexa paper has carried a journal expression of concern since 2021 1.
| Question | Short answer |
|---|---|
| What it is | A chemically capped fragment of angiotensin IV, a small peptide-like molecule |
| Where it came from | Joseph Harding and Jay Wright's lab, Washington State University |
| Human evidence | None published |
| Animal and cell evidence | Rats and cultured rat neurons, mostly one lab |
| Approval | Not approved by the FDA or any other regulator |
| How it is sold | Online, labeled 'for research use only' |
| Evidence strength | Very low (preclinical only) |
What is dihexa?
Dihexa is a shortened version of angiotensin IV with chemical caps on both ends, designed so the body breaks it down slowly. In rats, dihexa was absorbed when given by mouth and reached the brain 1. People buy dihexa online hoping for sharper memory, better focus, or faster recovery after a concussion. (Its chemical name is N-hexanoic-Tyr-Ile-(6) aminohexanoic amide.)
| When | Step in the dihexa story |
|---|---|
| Before 2013 | Earlier rat work links angiotensin IV and shortened versions of it to learning and memory |
| 2013 | The dihexa paper: absorbed by mouth, reaches the brain, better maze scores in impaired and aged rats 1 |
| 2014 | A paper proposes dihexa works through HGF/MET 2 |
| 2021 and 2025 | The journal flags both the 2013 and 2014 papers with expressions of concern (2021), then retracts the 2014 paper (2025) 1 2 |
| 2022 and 2024 | Athira Pharma's fosgonimeton, aimed at the same system, misses its main goal in two Alzheimer's trials 4 |
How dihexa is supposed to work
The proposed route from dihexa to new synapses, and the steps that rest on a retracted paper
Without the 2014 paper, there is no standing published explanation of how dihexa acts in the brain. We found no published work showing that the older idea, a brain binding site for angiotensin IV called AT4, explains dihexa's effects.
The 'ten million times stronger than BDNF' claim
Forum posts often repeat that dihexa is seven orders of magnitude (ten million times) more potent than BDNF, or brain-derived neurotrophic factor, a natural protein that helps neurons build connections. The figure was publicized by the lab behind the 2013 dihexa paper and refers to spine growth in cultured neurons from the rat hippocampus, the brain region that forms new memories 1. It compares how little of each molecule produced an effect in a dish. A concentration that works in a dish tells you nothing about the dose a person would need, whether the effect lasts in a living brain, or whether anyone's memory improves.
What the research shows
| Study | Model | What was measured | Status |
|---|---|---|---|
| McCoy et al., 2013 1 | Rat neuron cultures and rats | Spine growth in a dish; water maze scores in scopolamine-impaired and aged rats | Published; expression of concern (2021) |
| Benoist et al., 2014 2 | Rat cells and rats | Whether the effects depend on HGF/MET | Retracted (2025) |
| Human trials | People | Anything | None published |
In the McCoy study, rats given scopolamine (a drug that blocks memory) and old rats both found the hidden platform in a water maze faster after dihexa 1. The work came from one lab, the journal has since flagged the paper with an expression of concern, and no human trial has followed.
What happened when a related drug was tested in people
Athira Pharma, a company founded on this research, built fosgonimeton (ATH-1017), a different molecule that also aims to boost the HGF/MET system. In June 2022 fosgonimeton missed its primary endpoint, the main result the trial was designed to test, in the mid-stage phase 2 ACT-AD trial in mild to moderate Alzheimer's disease. In September 2024 it missed its primary endpoint and its key secondary endpoints in the larger phase 2/3 LIFT-AD trial 4.
Fosgonimeton is a different molecule from dihexa, so its result does not prove dihexa would fail. It is still the only test of the HGF/MET approach in patients, and it found no benefit on the main measures. A molecule can be potent in a dish and still do nothing measurable for people.
Is dihexa safe? Side effects and the cancer question
Nobody knows dihexa's side effects in people, because no study has measured them. A vendor page that says 'no reported side effects' is describing an absence of research.
The cancer concern comes from dihexa's proposed target. MET is a proto-oncogene, a normal gene that can drive cancer when it is overactive. Too much HGF/MET signaling drives tumor growth, invasion and spread in many cancers, which is why several cancer drugs block it 3. A compound designed to turn the same system up carries a theoretical tumor risk that no one has tested. Its long-term effects are also unknown.
Reddit reports of headache, insomnia and anxiety on dihexa cannot be checked. Buyers do not know what is in the vial, expect to feel sharper, and rarely post when nothing happened. Research-chemical products are made without manufacturing oversight, so the amount, purity and, for injectables, sterility of dihexa are unverified. There are no interaction studies, so anyone on prescription medicines, especially for cancer, seizures or blood pressure, has no evidence to go on.
Dihexa dosage: is there a safe dose?
There is no established human dose of dihexa, and this page does not give one. Rat doses cannot be converted to people without human pharmacology studies, and those have never been done. The oral, injected and skin-cream 'protocols' shared online are guesses; absorption by mouth was shown in rats only 1.
Is dihexa legal or FDA-approved?
The FDA has not approved dihexa for any use, and neither has any other regulator. Dihexa is a synthetic compound, not a recognized dietary ingredient, so it cannot lawfully be sold as a dietary supplement in the US. Sellers label it 'for research use only, not for human consumption', which places it outside the quality rules that cover medicines and supplements.
Any pharmacological substance which is not addressed by any of the subsequent sections of the List and with no current approval by any governmental regulatory health authority for human therapeutic use ... is prohibited at all times.World Anti-Doping Agency Prohibited List, section S0, Non-approved substances 5
WADA does not name dihexa, but dihexa has no approval from any health authority, so it falls under S0. Competitive athletes should treat it as prohibited in and out of competition.
Dihexa vs Semax, Selank, Cerebrolysin and lion's mane
| Compound | What it is | Human evidence | Status |
|---|---|---|---|
| Dihexa | Angiotensin IV analogue | None published | Not approved anywhere |
| Semax | Synthetic peptide based on part of ACTH, a stress hormone | Small studies, mostly Russian | Approved in Russia; not FDA approved |
| Selank | Synthetic peptide based on tuftsin, a small immune-system protein fragment | Small studies, mostly Russian | Approved in Russia; not FDA approved |
| Cerebrolysin | Peptide mix from pig brain | Clinical trials in stroke and dementia; benefit unclear | Approved in some countries; not FDA approved |
| Lion's mane | Edible mushroom | A few small memory trials | Sold as a supplement in the US |
Compounds with human data for focus and memory
If your memory or focus is slipping, check these first
Several causes of poor memory and brain fog are common, show up on routine blood tests and are often treatable. The NICE dementia guideline recommends blood tests including vitamin B12 and thyroid function to rule out reversible causes when someone is assessed for memory problems 6. B12 deficiency (treated with vitamin B12) and an underactive thyroid (hypothyroidism) both slow thinking, and low iron, poor sleep and unsteady blood sugar can sap focus. Memory loss that is new, getting worse, or comes with confusion, personality change or trouble finding words needs a doctor's assessment.
Markers to check before blaming your brain
Citations
- McCoy AT, Benoist CC, Wright JW, et al. Evaluation of metabolically stabilized angiotensin IV analogs as procognitive/antidementia agents. J Pharmacol Exp Ther. 2013;344(1):141-154. Expression of concern: J Pharmacol Exp Ther. 2021;378(3):313.
- Benoist CC, Kawas LH, Zhu M, 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: J Pharmacol Exp Ther. 2025;392(4):103567.
- Organ SL, Tsao MS. An overview of the c-MET signaling pathway. Ther Adv Med Oncol. 2011;3(1 Suppl):S7-S19.
- Athira Pharma. Topline results for fosgonimeton: phase 2 ACT-AD (June 2022) and phase 2/3 LIFT-AD (September 2024) in mild to moderate Alzheimer's disease. Company press releases.
- World Anti-Doping Agency. The Prohibited List, S0 Non-approved substances.
- National Institute for Health and Care Excellence. Dementia: assessment, management and support for people living with dementia and their carers (NG97), 2018.
Educational context only, not medical advice or a diagnosis. Always discuss your results with a clinician.
