Dihexa

Dihexa is a small peptide (a short chain of amino acids, the building blocks of proteins) made from a natural molecule called angiotensin IV. It got attention because of animal studies showing it could help neurons grow new connections and improve learning, along with a striking claim that it is far more powerful than a key brain growth factor called BDNF. You can buy it online as a nootropic (a “smart drug” meant to boost thinking). But the honest picture is much more cautious than the marketing. Dihexa has never been tested in people, the main study explaining how it works was retracted in 2025, and a closely related drug failed its big Alzheimer’s trial. This profile walks through what dihexa is, what people claim about it, and what the evidence really supports.

What it is

Dihexa (developmental code PNB-0408, chemical name N-hexanoic-Tyr-Ile-(6)-aminohexanoic amide, molecular formula C27H44N4O5, MW about 504.7, CAS 1401708-83-5) is a lab-made peptide based on angiotensin IV. Chemists tweaked both ends of the molecule so it would dissolve better in fat, survive longer in the body, be absorbed when taken by mouth, and cross the blood-brain barrier (the protective filter that keeps most substances out of the brain) more easily than the original peptide. It was developed by Joseph W. Harding and John W. Wright at Washington State University and commercialized through M3 Biotechnology, later renamed Athira Pharma.

The proposed explanation for how it works is this: dihexa is thought to grab tightly onto a molecule called hepatocyte growth factor (HGF) and boost the signal it sends through the c-Met receptor (a docking point on cells). That boosted signal is supposed to make brain cells in the hippocampus (the brain’s memory center) grow new connections, called synapses. The catch, explained below, is that the study that first established this HGF/c-Met mechanism has since been retracted. So treat it as “claimed in now-retracted work,” not as a settled fact.

The claims

Dihexa is sold as a powerful brain booster, and the pitch rests largely on one headline number: that it is roughly seven orders of magnitude (about ten million times) more potent than BDNF (brain-derived neurotrophic factor, a protein that helps neurons grow and survive) in a lab test. That figure comes from the original WSU team and is best read as a claim from that one group, not something other researchers have independently confirmed. The story that goes with it is that dihexa’s tight grip on HGF and its boost to c-Met signaling crank up the growth of new synapses. Online, some users say it sharpened their focus and memory.

It’s worth keeping two things separate here: whether the underlying biology is plausible, and how strong the evidence is for these specific numbers. That matters because the central claim about how dihexa works leans heavily on a study that has been formally retracted.

What the evidence actually shows

No human data exist. There are no published studies of how dihexa moves through the body, how toxic it is, or whether it works in people. No human clinical trials of dihexa itself have been registered or completed. The online nootropic reports are uncontrolled and can’t be verified.

The animal and cell evidence is real but limited, and the key mechanism study has been retracted. The most-cited supporting study is McCoy et al. 2013 (Journal of Pharmacology and Experimental Therapeutics, PMID 23055539). In it, oral dihexa reversed learning problems caused by scopolamine (a drug that blocks memory), improved spatial learning in aged rats, and increased the density of connections in the hippocampus. That paper is real and has not been retracted.

But the study explaining the mechanism, from the same group, was retracted in 2025:

• Benoist et al. 2014 (JPET), the paper that claimed the effect depends on HGF/c-Met, was retracted (notice published April 2025) after a WSU investigation found falsified data. The journal had already issued an Expression of Concern (a formal flag that something may be wrong with a paper) in September 2021, before the full retraction.

The upshot is that the “how it works” story is shakier than older articles make it look. The broader idea linking angiotensin IV, HGF, and cognition came before that paper, but the specific HGF/c-Met claim shouldn’t be cited as established, and the retracted Benoist work must not be cited as support at all.

The related drug that reached trials is a different molecule, and it failed. The compound that actually made it into human trials is fosgonimeton (ATH-1017, originally NDX-1017). It’s best described as a prodrug (an inactive form that the body converts into the active drug) of the dihexa-related active piece, not dihexa itself. It was advanced by Athira. Fosgonimeton failed its big Phase 2/3 trial, called LIFT-AD (NCT04488419, with roughly 315 participants randomly assigned to 40 mg or a placebo for 26 weeks, given subcutaneous (under the skin)). Announced in September 2024 and presented at the CTAD conference in October 2024, it missed both its main goal (GST change -0.08, P=0.70) and key secondary goals, though it was generally well tolerated, with some hints of benefit in a subgroup carrying the APOE ε4 gene and in biomarkers. Fosgonimeton is not dihexa, and it isn’t approved either. This is the closest thing to a human test of the underlying design, and it didn’t work.

Legal and regulatory status

Dihexa itself is research-grade only. It has no FDA approval and no marketed product, and all the dihexa-specific data come from rodents and cell cultures. It’s sold gray-market as a “research chemical” or nootropic and has no legal standing as a dietary supplement.

Its compounding status (whether pharmacies can legally mix it into custom prescriptions) is genuinely up in the air. “Dihexa Acetate” had been on the FDA’s 503A interim bulks list, Category 2. In a 2026 FDA update (reported around April 2026), Dihexa Acetate was one of 12 peptides removed from Category 2 and referred to the Pharmacy Compounding Advisory Committee (PCAC) for review, with that review expected before February 2027. Being removed from Category 2 does not mean it was approved or moved to Category 1, and it does not by itself make the substance eligible for 503A compounding. Treat this as reported but still provisional.

For athletes, dihexa is not listed by name on the WADA Prohibited List. But because it’s a pharmacologically active substance that no government health authority has approved for human use, it falls under category S0 (Non-Approved Substances), which is banned at all times, both in and out of competition. The S0 definition (drugs in pre-clinical or clinical development, plus designer, discontinued, and veterinary drugs) clearly covers it. You could also argue it’s secondarily relevant under the growth-factor rules given its proposed mechanism, but S0 is the clear basis.

Safety

Human safety is unknown. There are no toxicology or pharmacokinetic (how the body absorbs and clears a drug) data in people. Vendor “anecdotal side-effect percentages” and specific rodent liver-toxicity thresholds don’t trace back to any verifiable original source and should be treated as unsubstantiated.

The main theoretical risk is built into how it’s supposed to work. The HGF/c-Met pathway is a well-known driver of cancer, so a compound designed to boost c-Met signaling raises a believable concern that it could help tumors grow. No cancer-causing (carcinogenicity) studies in any species have been published for dihexa. Early statements from the developers that there was “no apparent toxicity” came from short-term lab work by a group whose related paper was later retracted, so they carry limited weight.

Bottom line

Dihexa is an interesting research molecule, not a proven brain booster. The evidence is thin and partly compromised: no human data at all, a retracted foundational mechanism paper, a failed pivotal trial for the related prodrug, and an unmeasured cancer-mechanism concern coming from its very target. The often-repeated “seven orders of magnitude more potent than BDNF” claim traces to the original WSU work and has never been tested in people. Anyone framing dihexa as a safe, effective nootropic is overstating what we actually know. This is not medical advice.

Evidence grade: 3/10 · Animal only.

Sources

• McCoy et al. 2013, metabolically stabilized Ang IV analogs as procognitive agents (JPET, PMID 23055539)
• Benoist et al. 2014, HGF/c-Met-dependent effects (JPET, PMID 25187433) — RETRACTED
• Retraction notice to Benoist 2014 (JPET, April 2025, PMID 40312093)
• Retraction Watch — Expressions of Concern on Athira-related papers (Sept 2021)
• Dihexa — Wikipedia
• Fosgonimeton / ATH-1017 LIFT-AD Phase 2/3 (NCT04488419)
• NeurologyLive — Synaptic agent fosgonimeton falls short in Phase 2/3 LIFT-AD trial
• Practical Neurology — Fosgonimeton fails to meet study endpoints
• ALZFORUM therapeutics entry — Fosgonimeton
• Athira Phase 1 PK/safety of fosgonimeton (PMC9108585)
• Frier Levitt — FDA peptide “Do Not Compound” / Category 2 update 2026
• FDA — Bulk Drug Substances Used in Compounding Under Section 503A
• WADA — 2026 Prohibited List now in force