Carl read the papersWhat it actually is
Dihexa came out of Washington State University from work on angiotensin IV, a six-amino-acid fragment of the brain renin-angiotensin system with long-noted effects on learning in rodents. Angiotensin IV breaks down fast and does not cross the blood-brain barrier, so the group cut it to its first three residues and modified both ends to make it stable and fat-soluble.
The result, N-hexanoic-Tyr-Ile-(6)aminohexanoic amide, is a three-residue backbone wearing two fatty tails. It is usually filed with the peptides and it behaves more like a small molecule: orally active and able to reach the brain, which is unusual enough that it became the selling point.
How it’s thought to work
- HGF and the MET receptor — The proposed mechanism is positive modulation of hepatocyte growth factor signalling through its receptor MET, which in the brain is associated with synapse formation.
- Synaptogenesis — The claim is formation of new dendritic spines and synapses rather than a neurotransmitter effect, which is where the comparisons to BDNF come from.
- Oral and brain-penetrant — Both were explicit design goals and both are reported in the original papers.
- An independent line — A 2021 study from a Chinese group reported that oral dihexa restored spatial learning in APP/PS1 mice and acted through PI3K/AKT, with reduced pro-inflammatory cytokines. That work is not from the original lab, which matters given what happened to the original lab's papers.
What the research says
This entry is mostly about what happened to the research. The foundational papers came from Washington State University between 2011 and 2014, including the 2012 paper describing the angiotensin IV analogues as HGF/MET modifiers and the 2014 paper arguing the procognitive effect depends on HGF/c-Met. Athira Pharma licensed dihexa from the university and, by its own account, tried to develop it from 2011 to 2015, then dropped it because the studies failed to show it had the characteristics needed to be a successful therapeutic product. In June 2021 the company announced an internal investigation into doctoral research by its chief executive, Leen Kawas, a co-author of those papers as a graduate student. An independent special committee reported on 21 October 2021, and Athira's filing with the SEC states its primary finding plainly: that Dr Kawas altered images in her 2011 doctoral dissertation and at least four research papers she co-authored while a graduate student, published from 2011 to 2014. She resigned effective 18 October 2021. In April 2025 the Journal of Pharmacology and Experimental Therapeutics published retraction notices for three of those papers, from 2011, 2012 and 2014. Separately, Athira's lead candidate fosgonimeton, which the same filing describes as a prodrug that metabolises into dihexa, completed a phase 2/3 trial in Alzheimer's disease: LIFT-AD missed its primary endpoint, with a between-group difference of -0.08 on the global statistical test, p=0.70, at 26 weeks. The company reported an acceptable safety profile, with more discontinuations for adverse events on drug (14.2%) than placebo (4.6%), mostly injection site reactions.
- Developed at Washington State University as a metabolically stabilised, orally active angiotensin IV analogue.
- Athira licensed it, worked on it from 2011 to 2015, and discontinued it because it lacked the properties needed to be a usable drug.
- Athira's October 2021 SEC filing: the special committee found altered images in the chief executive's dissertation and at least four co-authored papers from 2011 to 2014.
- Three of those papers carry retraction notices published in J Pharmacol Exp Ther in April 2025.
- Fosgonimeton, described in the same filing as a prodrug that metabolises into dihexa, missed its primary endpoint in the phase 2/3 LIFT-AD trial (p=0.70).
- Independent 2021 mouse work reported better spatial learning and lower inflammatory cytokines via PI3K/AKT, which is the strongest remaining support.
- No human trial of dihexa itself has ever been conducted.
Reported protocols
These are the doses the peptide community actually reports running (Reddit & forums), alongside published research — logged for education, not as a recommendation to use.
| Parameter | Commonly reported range |
|---|---|
| Human dose | Not established. Dihexa itself has never been through a clinical trial. Athira discontinued its development and moved to a different compound. |
| What the trials actually tested | The human data in this story belongs to fosgonimeton, a different molecule, given as a daily 40 mg subcutaneous injection under medical supervision in registered trials. Those are not dihexa doses, and the trial that mattered did not succeed. |
| Reported online | There is a long trail of first-hand posts, mostly on r/Nootropics, going back to 2014. The amounts people describe span roughly a thousandfold, from about a milligram to tens of milligrams, by mouth, under the tongue, through the skin in DMSO, and by injection. Reports range from dramatic memory effects to nothing at all at high amounts. A spread that wide is not a protocol, it is a sign that nobody knows what this does in a person. |
| Animal doses | The rodent work used oral dosing in milligrams per kilogram of animal body weight. Those figures do not scale across to a human regimen in any reliable way, which has not stopped people trying. |
| Carl's position | When the papers that justified a compound have been retracted and the drug built on the same chemistry failed its trial, inventing a dose for it is not a service to anyone. |
Common use cases
| Goal | Community protocol notes |
|---|---|
| A case study in research integrity | possibly the clearest one in the peptide world, and worth reading properly |
| Understanding the HGF/MET cognition idea | the target survives the scandal even if the original data did not |
| Reading the fosgonimeton trial results | a real phase 2/3 readout in Alzheimer's disease, published in full |
Mixing it (reconstitution)
Freeze-dried peptides must be reconstituted with bacteriostatic water before they can be measured. Carl’s calculator turns “mg in the vial + ml of water + target dose” into “units on the syringe” — and tells you how long the vial lasts.
→ Open the Reconstitution Calculator
Injection & handling
Dihexa is described as orally active, so injection is not the usual question here, and there is no administration guide on this page regardless. The reasons are specific. The foundational papers were retracted in 2025 after an investigation found altered images. The clinical programme that came out of this chemistry missed its primary endpoint. And the mechanism itself deserves a thought: MET is an oncogene, and a 2018 Nature Reviews Cancer review describes it driving transformation when altered and supporting cancer cell survival and spread when activated. A compound designed to turn that system up, with no human safety data of its own, is not something to experiment with on the basis of a potency figure from a retracted literature.
Stacks it appears in
- With Semax or Selank — the standard nootropic shelf pairing. Those have their own thin evidence, SAHPRA names both as examples of illegally marketed peptides, and nothing has been studied in combination.
- With P021 — both are small neurotrophic mimetics aimed at the same general idea from different directions, and neither has human data.
- With racetams or choline sources — common in forum protocols. No interaction work exists, which means nobody knows, rather than that it is fine.
Sources
- McCoy AT et al. 2013, J Pharmacol Exp Ther. Evaluation of metabolically stabilized angiotensin IV analogs as procognitive/antidementia agents (PMID 23055539)
- Retraction notice, J Pharmacol Exp Ther 2025, for Kawas LH et al. 2012, Development of angiotensin IV analogs as hepatocyte growth factor/Met modifiers (PMID 40312092)
- Retraction notice, J Pharmacol Exp Ther 2025, for Benoist CC et al. 2014, The procognitive and synaptogenic effects of angiotensin IV-derived peptides are dependent on activation of the HGF/c-Met system (PMID 40312093)
- Retraction notice, J Pharmacol Exp Ther 2025, for Kawas LH et al. 2011, Mimics of the dimerization domain of hepatocyte growth factor exhibit anti-Met and anticancer activity (PMID 40312094)
- Athira Pharma Form 8-K filed 21 October 2021, SEC EDGAR
- Porsteinsson AP et al. 2025, J Alzheimers Dis Rep. Fosgonimeton in mild-to-moderate Alzheimer's disease (PMID 41393340)
- Hua X et al. 2022, J Alzheimers Dis. Phase I trial of fosgonimeton in healthy volunteers and Alzheimer's subjects (PMID 35180125)
- Sun X et al. 2021, Brain Sci. AngIV-analog dihexa rescues cognitive impairment in the APP/PS1 mouse via PI3K/AKT (PMID 34827486)
- Comoglio PM et al. 2018, Nat Rev Cancer. Known and novel roles of the MET oncogene in cancer (PMID 29674709)
- ClinicalTrials.gov search for dihexa
- WADA 2026 Prohibited List, S0 non-approved substances
- SAHPRA, Peptide Products: Public Information (May 2026)
