Dihexa

What is Dihexa?

animal model

Dihexa is a laboratory-made molecule that began as a piece of angiotensin IV, a small hormone fragment the brain uses in learning and memory. Its makers wanted a version that would survive being swallowed and still reach the brain, which the natural fragments do badly. A 2013 rat paper describes the end result as an orally active, blood-barrier permeant, metabolically stabilized analog, which in plain terms means it can be taken by mouth, gets into the brain and is not broken down quickly.1 Whether to call it a peptide is a fair question, since it is searched for as one. A 2015 review answers it by calling Dihexa a small molecule, one derived from the pre-prototype molecule Nle1-angiotensin IV, a modified version of the hormone fragment.2 So it is peptide-derived rather than a peptide in the usual sense. It keeps two amino acids, tyrosine and isoleucine, and carries chemical caps on both ends that the natural fragment does not have. That is the reason it lasts, and it is also the reason no result for angiotensin IV can simply be read across to Dihexa.

What is Dihexa good for?

in vitro

In the research, Dihexa was built for one job, which is memory loss in brain diseases such as Alzheimer's and Parkinson's. The developers' 2015 review describes it as a molecule that shows promise in overcoming memory and motor dysfunctions by augmenting synaptic connectivity via the formation of new functional synapses.3 Synapses are the junctions where one nerve cell passes a signal to the next, so the idea is that more of them means better recall. A second 2015 review puts the target the same way, saying the molecule may be efficacious as a treatment for AD, the usual shorthand for Alzheimer's disease.2 Outside memory, it has been tried on hearing damage in fish and nerve repair in rats, both covered below. It also turns up as a plain laboratory tool: a 2016 stem cell protocol uses Dihexa, a hepatocyte growth factor agonist, with dexamethasone to turn stem cells into liver-like cells in a dish.4 None of those is a use in a person. In this literature, good for means tested on in an animal or a dish, and that is the meaning to carry through the rest of the page.

Does Dihexa improve memory?

systematic review

In rodents with a memory problem, the published answer is yes, and that qualifier is the whole story. The test used most is the Morris water maze, in which a rat or mouse learns where a hidden platform sits in a pool of water. In the 2013 rat work, Dihexa showed what the authors call excellent antidementia activity in the scopolamine and aged rat models.1 Scopolamine is a drug that blocks memory for a short time, and aged rats bring their own decline. A 2021 study in APP/PS1 mice, a strain bred to develop Alzheimer-like brain changes, found that Dihexa restored spatial learning and cognitive functions in the Morris water maze test.5 A 2018 systematic review of animal studies found that in models of cognitive deficit, eight of nine studies reported improved spatial working memory with angiotensin IV and its analogs, a group in which it lists Dihexa.6 Every one of those animals had a memory deficit, made for the experiment or brought by age. Whether Dihexa does anything to a healthy memory is a different question, and none of these experiments put it to a person.

Has Dihexa ever failed in an animal study?

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Yes, and the failure is one of the better-designed studies in the whole record. A 2024 study took forty male Wistar rats, randomised them into three groups, and gave two of the groups 3-nitropropionic acid, a toxin that copies the damage seen in Huntington's disease.7 One of those two groups also received Dihexa, under its code name PNB-0408, for the five weeks of exposure. The rats were scored on body weight, movement and memory, and their brains were examined afterwards. The result was a clear null: the authors report that PNB-0408 did not protect rats from the deficits induced by 3-NP neurotoxicity.7 That matters more than its size suggests. A literature this small needs its negative results read as carefully as its positive ones, and this one shows the memory effect seen after scopolamine does not carry over to every kind of brain injury. It is also a reminder that a result in one model is not a property of the compound, which is easy to forget when most of the record points one way.

What else has Dihexa been tested on?

animal model

Two lines of work sit outside memory, and each is a single experiment. The first is hearing: after testing it on the hair cells of larval zebrafish, which resemble the sensory cells of the human inner ear, the authors conclude that Dihexa holds clinical potential for mitigating chemical ototoxicity, meaning hearing damage caused by drugs.8 The damage came from two antibiotics known to harm hearing, and the fish were exposed for a short time in a dish. The second is nerve repair. In a 2021 study, rats had the sciatic nerve in one leg cut and stitched back together, and were followed for 16 weeks while their ability to feel and walk returned. The authors conclude that stem cells, G-CSF and Dihexa are promising candidates for adjunct therapies to promote limb functional recovery after surgical nerve repair in these rats.9 G-CSF is a growth signal for blood cells. Neither study has been repeated in the research behind this page, and a promising candidate in one rat experiment is a reason to run a second experiment rather than a result a reader can rely on.

Has Dihexa been tested in people?

review

Not in any study behind this page. A 2026 orthopaedic review that covers Dihexa alongside Semax and Selank sums up the field by saying that although preclinical studies are promising, there is a current lack of clinical trials.10 Every result on this page comes from rats, mice, zebrafish larvae or cells in a dish. None of the studies we could find gave Dihexa to a person, measured it in human blood, or recorded a single human side effect. That gap is not a detail to skim past. The compound was put forward as a possible Alzheimer's medicine more than a decade ago, and the step that would turn an animal result into a human one, a controlled trial, does not appear in these sources at all. Reports of what Dihexa does to a person's focus, mood or recall, wherever a reader met them, are not derived from any study cited here, and should be read as accounts rather than evidence.

What happened to the key Dihexa papers?

in vitro

Two papers at the centre of the Dihexa story have been withdrawn by their journal, and this is the single most important fact for anyone weighing the mechanism. In 2025 a retraction notice was issued for the 2014 paper titled The Procognitive and Synaptogenic Effects of Angiotensin IV-Derived Peptides Are Dependent on Activation of the Hepatocyte Growth Factor/c-Met System.11 That retraction followed a Notice of Concern published against the same paper in 2021.12 The retracted paper was the one reporting that dihexa binds with high affinity to hepatocyte growth factor, the finding on which the explanation of how Dihexa works was built.13 A 2012 paper from overlapping authors, Development of Angiotensin IV Analogs as Hepatocyte Growth Factor/Met Modifiers, was retracted in 2025 as well.14 The notices as indexed carry no abstract, so the reason is not stated in what we could read, and we do not guess at one. What it changes is plain enough: the mechanism now rests partly on withdrawn work, while the 2013 rat memory results and the 2021 mouse study stand or fall on their own.

Is Dihexa millions of times more potent than BDNF?

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That comparison is repeated widely online, usually with a very large multiplier attached. None of the studies behind this page makes it. Not one of their abstracts compares Dihexa with BDNF, a protein that helps nerve cells grow, or gives a potency ratio of any kind. The very small numbers in this literature belong to other molecules, measured in other tests. Norleual, a related angiotensin IV analogue that blocks rather than boosts the same system, competitively inhibited the binding of HGF to its receptor c-Met in mouse liver membranes, with an IC50 value of 3 pM.15 An IC50 is the concentration that halves an effect, and 3 pM is three trillionths of a mole per litre. The retracted 2012 paper reported its blocking molecules working in multiple cell types at concentrations down into the low picomolar range.16 Those figures describe blockers rather than Dihexa, measured on membranes and cells rather than brains, and one comes from a paper that has been withdrawn. The concentration reported for Dihexa itself, set out on the Dihexa dosage page, is more than a hundred thousand times larger than those picomolar figures. None of that can be read as a measure of Dihexa's strength in a living brain.

Is Dihexa a stimulant, and does it help with anxiety?

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Neither question was asked by the studies behind this page. They measured maze learning, walking, nerve function and brain inflammation, and none recorded alertness, wakefulness, heart rate or anxiety in any animal. The nearest result points somewhere unexpected. In a 2012 rat study, divalinal, a related molecule that blocks the same growth factor system, was infused into the brain before each daily methamphetamine injection and prevented acquisition of a learned preference for the place where the rats received methamphetamine.17 That shows the system Dihexa is meant to switch on takes part in drug-linked learning, as well as the memory a reader is hoping to improve. It says nothing about whether Dihexa itself stimulates, calms or does neither. It does mean that a compound built to strengthen new learning cannot be assumed to pick only the learning a person wants, and that is a question for a study rather than a reassurance.

How is Dihexa given in studies?

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Mostly by mouth, which is unusual for something in this category and was the point of building it. The 2021 mouse study describes Dihexa as a compound which can be orally administered and cross the BBB, the blood-brain barrier that keeps most substances out of the brain.5 The nerve-injury rats received it by several other routes as well, including into the repair site itself. The amounts, routes and timings behind each result, and the reasons none of them is a human figure, are taken apart on the Dihexa dosage page. That page also covers the questions readers ask about vials and mixing, which these studies do not reach.

What is known about Dihexa's side effects?

review

Very little, because nothing has been recorded in a person and the animal studies were not built as safety studies. The concern raised most often is about growth rather than any symptom. Dihexa is meant to work through c-Met, the receptor for hepatocyte growth factor, and that receptor is a growth switch. A 2015 review lists what activation of the c-Met receptor stimulates, starting with mitogenesis, motogenesis and morphogenesis, meaning cell division, cell movement and the shaping of tissue.2 That is why cancer comes up in discussions of Dihexa, and none of the studies behind this page tested it for effects on tumours either way. The full record, including what the animal studies watched for and who was left out of them, is on the Dihexa safety page.

Is Dihexa approved, and is it legal to buy?

in vitro

It is not approved as a medicine by any regulator in the records we could find. The research describes it as something still on the way: the 2015 zebrafish paper calls Dihexa a small molecule drug candidate.8 A drug candidate is a compound a developer hopes to take into trials. Whether a reader may legally buy it is a separate matter that depends on the country and on how it is sold, and published research is the wrong place to settle it. What the research can settle is the status of the evidence. Among these sources there is no approval, no reported human trial and no product information of the kind an approved medicine carries, so nothing printed on a label of material sold under this name has been checked against a study.

What is Dihexa compared or combined with?

Readers most often weigh it against Semax, another compound sold for memory and focus, and against Cerebrolysin and other nootropic peptides. Those questions belong to the Dihexa comparison page, which sets out what the research can and cannot say about each pairing. The short version is that the two compounds have very different records: Semax has small human studies behind it, set out on the Semax overview, while Dihexa has none among the research behind this page. The research itself compares Dihexa mostly with its own relatives, from the hormone fragment it came from to molecules built to do the opposite. That family is covered on the comparison page as well, together with the one experiment that ran it alongside stem cells and a growth signal.

How is Dihexa supposed to work?

animal model

Dihexa comes out of the brain's renin-angiotensin system, the hormone network better known for controlling blood pressure. A 2013 review notes that AngII and AngIV have been shown to play opposing roles regarding memory acquisition and consolidation in animal models, which is why a fragment of the system became a memory target.18 The developers' own review records that currently there is controversy over the identity of this AT4 receptor protein, meaning researchers disagreed about what the fragment acted on.3 The answer they settled on was a growth protein made in many parts of the body, hepatocyte growth factor, and the receptor it binds to, which is called c-Met. In the zebrafish work, Dihexa-mediated protection is attenuated by co-treatment with the HGF antagonist 6-AH, which fits that account.8 In mice, the 2021 study reports that Dihexa activated the PI3K/AKT signaling pathway, a cell-survival route.5 But the paper that first showed Dihexa binding to that growth protein has now been retracted. So the way it works is best read as a working idea rather than a settled fact, and the rest of the page should be read with that in mind.