Cognitive and neuro

Dihexa

The human evidence is negative and filed under another name

7 sections

Top of article
What it actually is
What it is supposed to do
What people take it for
The dose question
How to check you have the right molecule
What people get wrong
What is known about harm

What circulates: About 5 to 50 mg a day by mouth across vendor and community pages, no two agreeing
What was studied: No dose in a person that I could find
The gap: No published human dose to compare against
How long it lasts: In rats, 12.68 days after 10 mg/kg into a vein, and 8.83 days after 20 mg/kg into the belly cavity, that second figure resting on four animals. In the 65 Phase 1 participants who received the injected phosphate version, the active molecule lasted about an hour and a half after injection under the skin. Days against hours, and I found nothing published explaining the gap.

What it actually is

Dihexa is sold as a peptide, a short chain of the building blocks proteins are made from, and product pages describe it as a six amino acid one. It contains two, tyrosine and isoleucine, with a six carbon fatty chain capped on the front and a six carbon tail on the back. It came out of angiotensin IV, a fragment of the blood pressure hormone system that improves rat maze performance but is destroyed by enzymes: Joseph Harding's laboratory at Washington State University cut that fragment to a three amino acid core and capped both ends, so enzymes could not recognise it and it could reach the brain. The university spun it out as M3 Biotechnology, later Athira Pharma, now LeonaBio.

What it is supposed to do

It is not supposed to switch anything on by itself. The account in circulation is that it binds hepatocyte growth factor, a repair signal the body already makes, and sharpens it, and that account comes from the 2014 paper that was retracted in April 2025. The binding figure still quoted, 65 picomolar, meaning dihexa sticks to that growth factor very tightly, comes from the same retracted paper. That distinction is also what makes the famous comparison the wrong shape: dihexa sharpens a signal that is already there, while BDNF, a brain growth protein, does the whole job, so comparing them by concentration is like comparing how far you turn a volume knob against how much electricity the speakers draw.

What people take it for

People take it for memory and thinking, on the strength of a figure saying it is ten million times more powerful than BDNF, a brain growth protein. That is what it is sold and talked about for, not what it has been shown to do. No human oral dose of dihexa has been established in anything I could find, and the two trial registries return nothing under that name. The animal work is rat maze performance after the animals' memory had been chemically blocked, mice bred to develop Alzheimer's changes, and a rat Huntington's model in which it did nothing.

The dose question

What circulates: About 5 to 50 mg a day by mouth across vendor and community pages, no two agreeing
What was studied: No dose in a person that I could find; Every human figure belongs to fosgonimeton, dihexa with a phosphate group added so it can be injected

No studied dose to compare

There is nothing to compare against, because no human oral dose of dihexa has been established in anything I could find. Every human figure belongs to fosgonimeton, the same molecule with a phosphate group on it so it can be injected, given at 40 mg or 70 mg a day under the skin rather than swallowed. None of the vendor or community pages I opened carrying an oral figure showed its working. Converting the rat oral dose of 2 mg/kg by body surface area lands near 22.6 mg for a seventy kilogram adult, but that is arithmetic worked here rather than a derivation I found anybody publishing, and the published method divides the result by a further ten before anyone is dosed, which puts it at 2.26 mg.

Reported because it is what people use. Nothing here recommends any amount.

How long it lasts

In rats, 12.68 days after 10 mg/kg into a vein, and 8.83 days after 20 mg/kg into the belly cavity, that second figure resting on four animals. In the 65 Phase 1 participants who received the injected phosphate version, the active molecule lasted about an hour and a half after injection under the skin. Days against hours, and I found nothing published explaining the gap.

Route studied

In rats, into a brain fluid space, into a vein, into the belly cavity and by mouth. In people, only as the injected phosphate version, under the skin once a day.

Route used

By mouth. Dihexa does not dissolve in water, and the material sold to individuals is commonly supplied in DMSO, an industrial solvent that carries things through skin, which is how the rat work dosed it too.

How to check you have the right molecule

The check is the chemical name and the weight. Dihexa is N-hexanoic-Tyr-Ile-(6) aminohexanoic amide, and PubChem's record, CID 129010512, gives the formula C27H44N4O5 and an average weight of 504.7. That structure holds two amino acids, tyrosine and isoleucine, with a six carbon fatty chain on the front and a six carbon amide tail on the back, so a page describing a six amino acid peptide is describing something other than dihexa. The second check is the name attached to any human evidence you are shown. The trials belong to fosgonimeton, the injected prodrug also called ATH-1017, which is this molecule with a phosphate group on the tyrosine so it can be injected, and that phosphate comes off again in the blood to release dihexa, which the Phase 1 paper calls ATH-1001. Search the United States government's trial registry for dihexa itself and nothing comes back; the European register answers that the query did not match any clinical trials.

Walked through on two real certificates in how to read a certificate of analysis.

What people get wrong

Every vendor page I have seen says dihexa has never been tested in humans. That is true of the exact molecule and not of the molecule with a phosphate on it, which went into a trial of 554 people with Alzheimer's disease, was given to 331 of them, and did not separate from the dummy injection. The number doing the selling is in worse shape than that. Ten million times more powerful than BDNF traces to a Washington State University press release dated 11 October 2012, and I searched the full texts of both founding papers for BDNF and for brain-derived neurotrophic factor and found neither in either. Three of the four papers the compound rests on were retracted in April 2025, and the fourth, which carries every rat dose, spine count and half life anybody quotes, has been under an expression of concern since September 2021, meaning the journal has flagged it without withdrawing it.

What is known about harm

The Alzheimer's Drug Discovery Foundation put the safety record in one line in 2021: there are no publications documenting the long term safety of dihexa in humans or animals. I found nothing published since that changes it. The hazard people raise is cancer, because the system dihexa is meant to amplify is a well documented driver of tumour growth and spread, and the same review calls that theoretical and untested. The numbers that do exist belong to the injected version. Across 549 people through thirty weeks there were no deaths in any group, serious events ran 15 of 218 on the dummy injection against 11 of 224 at 40 mg and 3 of 107 at 70 mg, and injection site reactions ran 14 percent of the dummy arm against 57 percent at 40 mg and 73 percent at 70 mg, with Alzforum recording that the higher dose arm was stopped mid-trial. Two people came off the Phase 1 study, one for a fall in neutrophils, a type of white blood cell, at 40 mg, and one for an allergic skin reaction at 80 mg.

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