Dihexa

What is dihexa?

Angiotensin is part of the renin-angiotensin system, which regulates blood pressure; this system also has a separate branch in the brain. The six-amino-acid angiotensin IV and some of its analogs have long been reported to facilitate learning and memory in animal experiments. However, these peptides are rapidly broken down in the blood and cannot cross into the brain, which has prevented their development as drugs. ^[1]

A research group at Washington State University chemically modified the first three amino acids, which carry the memory effect, of an angiotensin IV-like peptide and obtained a more stable and more fat-soluble molecule. This compound, whose chemical name is N-hexanoic-Tyr-Ile-(6)-aminohexanoic amide, was named “dihexa.” According to the authors, dihexa is a molecule that is orally active in rats, can cross the blood-brain barrier, and is metabolically stable. ^[1]

The legal and scientific meaning of the “for research purposes, not for human use” label, common on unlicensed peptides and peptide-like substances, is covered in a separate guide.

What did the animal studies show?

Rat experiments (2013). The paper describing dihexa used two memory models. In the first, scopolamine, which temporarily impairs memory, was given to rats, and the time the animals took to find a hidden platform in a pool of water (Morris water maze) was measured; when dihexa was given directly into the brain, into the abdomen, or orally, it corrected this learning impairment in a dose-dependent manner, partially at some doses (8–10 animals per group). ^[1] In the second model, 6 aged rats at 24 months, 3 male and 3 female in each group, were used; the learning curve of the dihexa group differed significantly from the group that did not receive it (P<0.03). The authors note that the aged rats were not pre-screened for cognitive impairment. ^[1] The same paper reported that dihexa increased dendritic spine and synapse formation in cultured rat hippocampal neurons. ^[1]

Alzheimer mouse model (2021). An independent group from China tested different dihexa doses in APP/PS1 mice, which develop Alzheimer-like amyloid accumulation. Dihexa improved learning in the water maze, increased neuron count and the level of a synaptic protein, and reduced activation of brain immune cells and inflammatory cytokines. The authors link the effect to the intracellular signaling pathway PI3K/AKT and declare no conflict of interest. ^[5]

These findings belong to animal models. The scopolamine model impairs memory artificially and briefly; Alzheimer mouse models mimic only part of the human disease. Having 6 animals per group in the aged rat experiment also increases the fragility of the result. ^[1]

Retracted papers and papers with notices of concern

Correction notes in the publication record are decisive for evaluating dihexa’s scientific background:

• Notice of concern (2021): In September 2021, the journal that published the 2013 paper describing dihexa added a notice of concern. ^[2] A notice of concern is not a retraction decision; it is a note by which the journal alerts readers about a paper.
• Retraction of the mechanism paper (2025): The 2014 paper proposing that dihexa’s memory effect runs through hepatocyte growth factor (HGF) and its receptor MET (c-Met) was retracted in April 2025. According to the retraction notice, the university’s investigation found fake and/or fabricated data in some figures of the paper and in the data in a later-submitted correction request, and two authors were held solely responsible. ^[3]
• Second retraction (2025): The 2012 paper from the same group describing angiotensin IV analogs as HGF/MET modulators was also retracted in the same journal. ^[4]

These records show that dihexa’s most-cited explanation, “it forms synapses through HGF/MET,” cannot be considered a proven mechanism today. The independent mouse study, by contrast, explained the effect through a different signaling pathway. ^[5]

Has dihexa been studied in humans?

No. On the page where FDA evaluates substances proposed for use in compounding, it makes the following finding for dihexa acetate: no human exposure data could be found for products containing dihexa by any route of administration, and FDA lacks important information about safety concerns, including whether the substance would cause harm when given to humans. ^[9] As of October 19, 2026, a “dihexa” search on ClinicalTrials.gov shows no registered study. ^[8]

The closest human data come not from dihexa but from another small molecule, fosgonimeton, developed to modulate the same HGF/MET system positively. In the randomized, placebo-controlled phase 2/3 LIFT-AD study in mild-to-moderate Alzheimer’s patients, the primary analysis was done with 287 people not using acetylcholinesterase inhibitors. The study did not reach its primary and secondary outcomes: at week 26, the combined score difference was −0.08 (p=0.70), the cognitive scale difference −0.70 (p=0.35), and the daily living scale difference +0.67 (p=0.61). The authors note that these small and non-significant differences favored fosgonimeton. Discontinuation because of side effects was 14.2% in the fosgonimeton group and 4.6% in the placebo group and was mostly due to injection site reactions. Five of the authors are employees or former employees and shareholders of the company developing the drug, and one is a shareholder who was the company’s medical director between 2019 and 2024 and later became its consultant. ^[7] This result cannot be transferred directly to dihexa; however, it shows that a human trial aimed at the same biological target did not show significant benefit in cognition.

HGF/MET and cancer: a theoretical concern

HGF and its receptor MET form a growth signaling system that normally has roles in tissue repair and development. However, genetic and biochemical data have shown that this system plays a causal role in the hallmarks of cancer, namely uncontrolled cell survival and growth, new blood vessel formation, and spread to distant organs; for this reason, antibodies and small molecules that block MET have been developed as cancer treatments in many solid tumors. ^[6]

The effect proposed for dihexa, by contrast, is in the opposite direction, namely strengthening this signal. This raises a theoretical concern that long-term use, especially in people with a known or not yet diagnosed tumor, might increase the growth signal. This concern is not a tested finding: there are neither animal nor human data on dihexa’s cancer risk, and the paper claiming to show the HGF/MET mechanism has been retracted. ^[3] The same uncertainty works in both directions: an unproven mechanism does not allow either benefit or harm to be predicted with confidence. FDA’s finding that no human safety data exist applies here as well. ^[9]

For general peptide risks and injection-related problems: Peptide side effects.

What do FDA and other regulators say?

• FDA, compounding list: Dihexa acetate had been nominated for the list of substances that can be used in drug compounding in pharmacies in the US. On FDA’s page dated April 22, 2026, the substance appears in the table of substances “nominated but withdrawn by the nominators,” on the grounds that no human exposure data exist. ^[9]
• The 2026 process: According to a law firm summary, FDA had placed more than a dozen peptides in category 2 (significant safety risk) in September 2023; on April 15, 2026, the US Secretary of Health announced that 12 peptides, including dihexa acetate, had been removed from category 2 because the nominators withdrew their nominations. According to the same summary, leaving category 2 does not automatically confer category 1 status, and the FDA advisory committee will consider dihexa acetate at a meeting to be held before the end of February 2027. ^[10]
• None of these processes is a drug approval; according to FDA’s finding, not even human exposure data exist for dihexa. ^[9]

Is dihexa prohibited in sport?

The WADA 2026 Prohibited List does not name dihexa. The list’s S0 class prohibits at all times pharmacological substances not covered in any other section of the list and not approved by any governmental health authority for human therapeutic use. The S2.3 class names hepatocyte growth factor (HGF) and also covers “other growth factors or growth factor modulators” that affect muscle, tendon, or ligament protein synthesis, vascularization, energy utilization, or regenerative capacity. Both classes are prohibited at all times, in and out of competition. ^[11] The list contains no separate classification for dihexa, and the classification of a specific substance is within WADA’s authority; because it is a substance not approved by any authority, both definitions are relevant for licensed athletes.

What is the status of dihexa in Türkiye?

A guide covering the legal status of peptides in general: Are peptides legal? Another peptide whose cognitive effects are discussed: Semax.

Evidence table: claim, population, and limits

Limits of this guide

This page summarizes published animal studies on dihexa, correction notes in the publication record, and official documents. It contains no individualized dose, preparation, method of administration, cycle length, or product source. Evaluating treatments with evidence and a license for memory problems and dementia is the physician’s task. Regulatory status may change; the information on this page is valid as of October 2026.