Dihexa research: what the published studies show

Three Retracted Papers

Three papers underpinning the hepatocyte growth factor and Met mechanism attributed to this compound have been retracted by the journal that published them.^[3][4][5] They are PMIDs 22129598, 25187433 and 21859930, all in the Journal of Pharmacology and Experimental Therapeutics.

Each is marked as a retracted article and each also carries an expression of concern. No finding from any of the three appears on this page, and the mechanism they described is not stated here as a mechanism.

That mechanism has not been independently replicated in the retrieved record. Any description of this compound as an HGF or c-Met modifier rests on retracted work.

The Surviving Development Study, and Its Own Unresolved Concern

A 2013 study set out to chemically modify the tripeptide Nle-Tyr-Ile to improve metabolic stability and barrier permeability.^[1] That tripeptide had been identified as carrying the core structural information behind the activity of an angiotensin IV analogue.^[1]

The result was Dihexa, described as orally active, blood-barrier permeant and metabolically stabilized, with reported activity in the scopolamine and aged rat models and marked synaptogenic activity.^[1]

The authors write that the data suggest dihexa may have therapeutic potential where augmented synaptic connectivity would be beneficial.^[1] Both hedges are theirs.^[1] This paper appeared in the same journal as all three retracted papers and shares authors with them.^[1] That does not invalidate it, and it does mean it is not independent of them.^[1]

This paper has not been retracted, but it carries its own expression of concern, issued by the same journal in 2021, the same year as the notices later attached to the three papers that were retracted in 2025.^[1] The notice does not state a reason. No finding on this page rests on a source that is free of either a retraction or an unresolved expression of concern.^[1]

An Independent Negative Result

A 2024 study tested the compound, named as PNB-0408, in rats given 3-nitropropionic acid, a mitochondrial toxin used to model a different neurodegenerative disorder.^[2]

Exposure to the toxin reduced weight gain, impaired spatial learning and memory consolidation, and produced marked motor dysfunction, and the compound did not protect the animals from any of it.^[2]The authors conclude it may not be an efficacious strategy in this preclinical model, and call for further research in alternative models.^[2] This is the only result on the page from a group unconnected to the original program.^[2]

State of the Evidence

Two citable papers support this page and they point in opposite directions.^[1] One reports oral activity and cognitive effects in two rat models.^[1] The other reports no effect on any outcome measured.^[2]

The negative result is the independent one.^[2] It comes from a different group, in a different journal, eleven years later, in a model the first paper did not test.^[1] Different models can give different answers, and this page reports both without reconciling them.

The retractions shape everything above. Three papers were withdrawn, each also carrying an expression of concern, and among them is the study that gave this compound the mechanism it is usually described by.^[3][4][5] A page describing what this compound does to synapses, or to HGF and c-Met signaling, would be citing withdrawn work or work that depends on it.

Nothing here is a clinical trial. No human study of this compound was retrieved, and nothing on this page describes what it does in a person.