Dihexa

What is dihexa?

Dihexa is a small peptide built as a metabolically stabilized analog of angiotensin IV, a fragment of the brain's angiotensin signaling system. Native angiotensin IV breaks down fast in the body, so researchers modified its structure to last longer and stay active, which is what "metabolically stabilized" means (McCoy et al., 2013, PMID 23055539). Dihexa carries the research code PNB-0408 and the chemical name N-hexanoic-Tyr-Ile-(6) aminohexanoic amide. It came out of academic neuroscience work at a university lab on how angiotensin-derived peptides affect learning and memory pathways. It is a research chemical. It is not a medicine, and it has not been approved for human use.

How does dihexa work?

Dihexa's mechanism is unsettled, and part of the published record on it has been withdrawn. Two competing ideas exist.

The first idea is the hepatocyte growth factor (HGF) and c-Met pathway. HGF is a signaling protein, c-Met is the receptor it binds, and together they support cell growth, survival, and synapse formation in the brain. The paper that argued dihexa works by potentiating HGF/c-Met (Benoist et al., 2014, J Pharmacol Exp Ther) was retracted in April 2025 after an institutional investigation found the figures contained falsified or fabricated data (Retraction notice, 2025, PMID 40312093). A retracted paper cannot support a claim, so its picomolar synaptogenesis numbers should not be treated as evidence. The HGF/c-Met idea itself did not vanish with the paper: a dihexa-derived drug candidate, fosgonimeton, was developed as an HGF/MET positive modulator and studied in people, which is the strongest surviving support for that mechanism (Athira Pharma, LIFT-AD program, 2024).

The second idea predates dihexa and comes from its parent compound. Angiotensin IV is thought to act largely by inhibiting insulin-regulated aminopeptidase (IRAP), an enzyme linked to memory, rather than through a classic receptor (reviewed for the angiotensin IV class). Because dihexa is an angiotensin IV analog, IRAP inhibition is a plausible route that researchers still discuss. Which mechanism, if either, drives dihexa's animal effects is not resolved.

What both ideas share is that this is a neurotrophic, growth-and-signaling story, not a stimulant one. Dihexa is not described as pushing neurotransmitter release the way a stimulant does.

What does the research on dihexa actually show?

The dihexa evidence base is preclinical: laboratory cell cultures and rodent models, with nothing published in humans, and one key paper retracted.

The main surviving finding comes from an animal paper (McCoy et al., 2013, PMID 23055539). In that work, orally dosed dihexa reversed a drug-induced memory deficit and improved learning in aged rats in a water-maze task, and the authors reported synapse-building activity in culture. Two cautions apply. First, this paper carries a 2021 editorial Notice of Concern about the reliability of some figures, so its results are best read as suggestive, not settled. Second, the closely related 2014 mechanism paper from the same lab was later retracted outright for fabricated data (PMID 40312093), which is a reason to hold the whole line of work loosely.

The most informative human-adjacent data is not about dihexa itself but about fosgonimeton, a compound developed from dihexa research. Fosgonimeton reached phase 2 and 3 Alzheimer trials, but the pivotal LIFT-AD study announced in 2024 that it did not meet its primary cognitive endpoint (Athira Pharma, 2024). When you see human claims about dihexa online, they are extrapolations from animal data or from this separate drug program, not human results for dihexa.

Is there a standard dihexa dosage?

No. There is no established human dose for dihexa, because no human trials of dihexa have been published, so any figure you find is not backed by human research.

The only dosing published research anchors is animal dosing, such as the oral rat doses used in the 2013 study (McCoy et al., 2013, PMID 23055539), and even that sits under a Notice of Concern. Animal dosing does not translate directly to people, and a concentration in a dish is not a human dose, route, or schedule. For that reason we do not list a human dose and we do not tell anyone how much to use. Decisions about any compound belong with a qualified clinician who can weigh your health, your medications, and the fact that dihexa has no human safety record.

What are the reported side effects and safety concerns of dihexa?

Because human trials of dihexa have not been published, its human side-effect profile is unknown, and the concerns below come from its mechanism and general biology, not from documented human events.

• No human safety data: there is no published record of adverse events in people taking dihexa, which is a limitation, not a clean record.
• Mechanism-based caution: HGF/c-Met signaling participates in cell growth and tissue repair throughout the body. Some researchers have raised theoretical questions about potent, long-acting potentiators of this pathway. These questions have not been studied in people taking dihexa, because no such studies exist.
• Evidence-integrity caution: a core dihexa paper was retracted for fabricated data and another carries a Notice of Concern, so the underlying preclinical picture is less solid than a raw citation count suggests (PMID 40312093).
• Product quality: research chemicals vary in purity and identity between suppliers, so what is in a vial is not guaranteed to match the label.
• Regulatory status: dihexa is not approved for human use and is sold for laboratory research only.

How does dihexa compare to semax and selank?

Dihexa, semax, and selank are all peptides studied in cognitive and neurological research, but they act through different proposed pathways and have different amounts of published data.

Dihexa's studied mechanisms are HGF/c-Met potentiation (from a now-retracted paper) and, by class, IRAP inhibition, with its supporting animal data under a Notice of Concern (McCoy et al., 2013, PMID 23055539). Semax and selank are separate peptides with their own research literature and mechanisms. If you are comparing options, read each compound on its own terms rather than assuming they are interchangeable. See our semax and selank pages for their specific mechanisms and research context.