Dihexa

Mechanism

Dihexa (also called PNB-0408 or N-hexanoic-Tyr-Ile-(6) aminohexanoic amide) is a hexapeptide derivative of angiotensin IV (AT4), the C-terminal fragment of angiotensin II. The Harding lab synthesized it as part of a program studying angiotensin IV’s effects on memory and cognition.

The proposed mechanism (multiple, partially characterized):

1. HGF/c-Met agonism — dihexa is hypothesized to bind hepatocyte growth factor (HGF) or its receptor c-Met, activating signaling that promotes neurite outgrowth, dendritic spine formation, and synaptogenesis
2. Augmentation of HGF-mediated cell survival — relevant in neurodegenerative contexts where HGF signaling is reduced
3. Possible effects on insulin-regulated aminopeptidase (IRAP) — the original angiotensin IV target, though dihexa’s selectivity profile differs

The “300x more potent than BDNF” claim that anchors gray-market marketing comes from an in vitro assay measuring spine density in dissociated hippocampal neurons, where dihexa appeared more potent than BDNF on a molar basis at low concentrations. This is a single in vitro readout in a single experimental system — the leap from “more potent in this specific assay” to “more potent for cognitive enhancement in humans” is unsupported by the cited evidence.

What the evidence shows

Animal preclinical (Harding lab, 2010s):

• Multiple rodent studies showing improved performance on memory tasks (Morris water maze, fear conditioning) after oral or systemic dihexa administration
• Increased dendritic spine density in CA1 hippocampal neurons
• Suggestion of efficacy in animal models of Alzheimer’s disease and traumatic brain injury

The pattern of the animal data is consistent with HGF/c-Met agonism producing pro-cognitive effects in rodent neurodegeneration models. The replication base outside the Harding lab is thinner than would be ideal.

Human clinical trials: None have been published. ClinicalTrials.gov shows no registered active trials with dihexa as the intervention. There has been no Phase 1 human PK/safety study published despite the molecule’s commercial availability through compounding and gray-market channels for nearly a decade.

Gray-market enthusiasm: Dihexa is widely sold and promoted in cognitive-enhancement and biohacker contexts. User reports are anecdotal and overwhelmingly positive in tone, but anecdote about cognitive enhancement is particularly unreliable — placebo effects on subjective cognitive measures are large, and confirmation bias in self-experimentation communities is strong.

Dosing literature

There is no approved or studied human dose. Gray-market protocols cite:

• Oral or transdermal: 8–32 mg/day (which would be very high — most peptide therapies operate at micrograms or low milligrams)
• Cycle structure: Highly variable; some users cycle weekly or with extended breaks

The lack of human PK data means even basic questions like “what dose produces what plasma level” are unanswered. The doses cited in user protocols are extrapolated from rodent studies, and rodent-to-human dose extrapolation for novel peptides is unreliable without bridging human PK studies.

We do not endorse a dose. The numbers above describe gray-market practice, not clinical recommendation.

Risks and adverse events

In gray-market use:

• Reports are largely anecdotal and overwhelmingly positive (subject to confirmation bias)
• Some users report headaches, mild GI upset, sleep disturbance
• Rare reports of more concerning effects (mood changes, anxiety) but causation is impossible to establish without controlled trials

Theoretical concerns:

• HGF/c-Met signaling is a known oncogenic pathway — c-Met activation drives proliferation in multiple cancer types. Chronic agonism of a pathway with known cancer-promotion biology is exactly the concern we’ve flagged for IGF-1 LR3 (different mechanism, similar concern category).
• No long-term safety data exists in any species at the doses gray-market users employ
• Compounding in non-clinical settings means quality, identity, and purity are not verified

Quality concerns specific to gray-market product:

The hexapeptide-derivative structure with non-natural modifications is harder to synthesize cleanly than simpler peptides. Mass-spec verification of gray-market dihexa is rare; some products sold as dihexa may not be the correctly modified molecule.

Regulatory status

The compound has been the subject of research patents but never advanced to a sponsored clinical development program — partly because the underlying patent landscape has been complicated and partly because no commercial sponsor has scaled the necessary human trial work.

Where to get it

We do not route readers to a fulfillment partner for dihexa. The combination of unapproved status, absence of human clinical evidence, theoretical c-Met-related cancer-promotion concern, and gray-market quality variance puts this firmly outside what we’ll endorse.

If a clinical trial program ever begins, the legitimate access path is enrollment in that trial. (See How we make money.)

References (selected)

1. McCoy AT et al. Evaluation of metabolically stabilized angiotensin IV analogs as procognitive/antidementia agents. J Pharmacol Exp Ther 2013. PubMed
2. Wright JW, Harding JW. The brain hepatocyte growth factor/c-Met receptor system: a new target for the treatment of Alzheimer’s disease. J Alzheimers Dis 2015.
3. Benoist CC et al. Facilitation of hippocampal synaptogenesis and spatial memory by C-terminal truncated Nle1-angiotensin IV analogs. J Pharmacol Exp Ther 2014.
4. Note: the absence of any registered human clinical trials, despite year