Dihexa
PNB-0408, N-hexanoic-Tyr-Ile-(6) aminohexanoic amide, Angiotensin IV analog
The Ground Truth Score
four plain questions, never one numberThe two papers that explained how it works were retracted for data fabrication in 2025. No human trial has ever been run. This is one of the riskiest gambles in the nootropic space.
Bottom line
Dihexa is a synthetic angiotensin IV analog developed at Washington State University that was promoted as a potent synaptogenic agent via the HGF/c-Met pathway, but the two core mechanistic papers underpinning that claim were formally retracted in April 2025 after an investigation found falsified figures, no human trial of any kind has ever been completed, and the compound's theoretical mechanism activates a known cancer-promoting pathway.
Does the science back it?
Do real people feel it?
Is it safe?
Could it be placebo?
"Do real people feel it?" is anecdote, not proof, weighted up because the science is thin, never because it beats a trial. And "could it be placebo?" is not an insult: if you feel better, that's real to you. The point is only to know whether you're paying peptide prices for an expectation.
Why is the evidence this thin? It's mostly economics →
Dose at a glance
full dosing ↓No established human protocol. Community reports: 5-20 mg oral or transdermal (DMSO carrier) 1-3x per week. No human PK data exists.
Reported, not prescribed. Verify your vial and your math.
The gist
- Self-experimenters report sharper recall and focus. The animal studies behind that claim were retracted for data fabrication in 2025.
- The two mechanistic papers that explained how it works were formally retracted by WSU in April 2025 after fabricated figures were confirmed. The HGF/c-Met story it was sold on is now unsupported in peer-reviewed literature.
- It activates a well-documented cancer-promoting signaling pathway and has never been tested in a single human safety trial. Every dose is a completely uncharted gamble.
First documented human use
No controlled human trial has been completed.
The pitch
What people claim it does
Stated plainly and neutrally, exactly as you'll hear it. I grade each one below.
- Promoted as millions of times more potent than BDNF at promoting synapse formation
- Claimed to cross the blood-brain barrier and directly amplify HGF/c-Met signaling in the brain
- Marketed as a potential treatment or preventive for Alzheimer's and other dementias
- Described as reversing cognitive deficits in rodent models of neurodegeneration
- Sold as a research chemical nootropic superior to racetams and other cognitive enhancers
The data behind each bullet
What actually backs it
Dihexa promotes synaptogenesis at picomolar concentrations, making it far more potent than BDNF
Based on in vitro assays from the McCoy et al. 2013 rodent study (PMC3533412), which remains under Expression of Concern since 2021. The 10-million-fold potency figure circulated online is a misreading of the original data; the actual reported figure was approximately 1,000-fold over BDNF in cultured hippocampal neurons. No human data exists.
McCoy et al. 2013, PMC (Expression of Concern flagged) ↗Dihexa reverses cognitive impairment in animal models via HGF/c-Met pathway activation
The two primary mechanistic papers establishing this claim (Kawas 2012 PMID 22129598; Benoist 2014 PMID 25187433) were both formally retracted in April 2025 following a Washington State University investigation that confirmed figures were falsified and/or fabricated by co-author Leen Kawas. Behavioral rodent data in the McCoy 2013 paper (Expression of Concern) remains the only non-retracted published evidence, and it is animal-only.
Retraction notice for Benoist 2014, PubMed PMID 40312093 ↗HGF/c-Met agonism improves cognitive outcomes in neurodegenerative disease
The related small-molecule HGF mimetic fosgonimeton (ATH-1017, from Athira Pharma, whose former CEO Leen Kawas was the data-fabricating researcher) ran two human trials in Alzheimer's patients. The ACT-AD Phase 2 (2022) missed its primary and secondary endpoints when used alongside standard of care; monotherapy exploratory signals were mixed and not definitive. The subsequent LIFT-AD Phase 2/3 trial (topline results September 3, 2024, n=315, 26-week randomized double-blind placebo-controlled) also failed to meet its primary endpoint (Global Statistical Test) and key secondary endpoints (ADAS-Cog11, ADCS-ADL23). Both trials failed. This is the closest human evidence for the compound class and both data points are negative.
NeurologyLive coverage of fosgonimeton ACT-AD Phase 2 results ↗Dihexa is orally bioavailable and can cross the blood-brain barrier
Oral bioavailability of approximately 50-60% and CNS penetration have been reported in rodent pharmacokinetic studies only. No human pharmacokinetic data has been published. Whether these properties translate to humans is entirely unknown.
Dihexa compound entry, MedChemExpress (PNB-0408) ↗Dihexa is safe for human self-experimentation at 5-30 mg per day
No Phase 1 safety study has ever been conducted in humans. Rodent data shows dose-dependent hepatotoxicity (elevated ALT/AST) at higher doses; published reports suggest a threshold somewhere above 1-5 mg/kg but this figure is disputed across studies and no single clean threshold is established. A 2016 rat study at 0.5 mg/kg/day for 12 weeks showed no hepatotoxicity; the precise floor remains unknown. The compound activates the HGF/c-Met pathway, which is one of the most well-documented oncogenic signaling axes in human cancer biology. There is no human safety data of any kind. The cited source is a community wiki with no primary references; no peer-reviewed human safety data exists to cite.
Peptide Protocol Wiki: Dihexa side effects and safety profile (community wiki, no primary sources; cited as the only available summary, not as evidence) ↗Mechanism
How it's assumed to work
Assumed · theoretical pathway
ASSUMED (theoretical, foundational papers retracted): Dihexa was proposed to bind hepatocyte growth factor (HGF) with high affinity (Kd around 65 pM), stabilize its active dimeric form, and thereby amplify signaling through the c-Met receptor tyrosine kinase. This was theorized to promote synaptogenesis and dendritic spine formation in hippocampal neurons. The proposed advantage over HGF itself was that Dihexa is small enough to cross the blood-brain barrier where HGF cannot. However, both papers establishing this mechanism (Kawas 2012 and Benoist 2014) were formally retracted for data fabrication in April 2025. The mechanism is therefore currently unsupported in peer-reviewed literature. An alternative IRAP (insulin-regulated aminopeptidase) mechanism for angiotensin IV analogs exists in the literature and may partially explain some effects if any are real.
Dosing & handling
What users and clinicians report
Community reports describe oral or sublingual doses of 5-30 mg per day, with 10-15 mg the most cited range. Some users report transdermal application with DMSO as a penetration enhancer. Cycling of 4-6 weeks on followed by 2-4 weeks off is commonly recommended in forums, theoretically to avoid receptor desensitization and limit continuous HGF/c-Met activation.
These doses are entirely community-derived with no clinical basis. No Phase 1 dose-escalation study has been done in humans. Rodent hepatotoxicity data means there is no safe floor known for humans. The DMSO transdermal route is particularly uncontrolled and adds systemic exposure risk from a carrier that pulls compounds through skin non-selectively.
Timing & food
No evidence-based timing guidance exists. Community protocols typically describe morning dosing to avoid any reported sleep disruption. No data on whether timing affects CNS penetration or effect duration.
Half-life
Unknown in humans. Animal pharmacokinetic studies suggest extended duration relative to earlier angiotensin IV analogs due to the metabolic stabilization introduced in the PNB-0408 design. No human half-life data exists.
Reconstitution sensitivity
Dihexa is typically sold as a raw powder. It has reported poor water solubility; many community protocols dissolve it in DMSO, ethanol, or PEG-400 before use. Standard peptide reconstitution in bacteriostatic water is not reliable due to solubility limitations. Solubility must be confirmed in chosen vehicle before dosing.
Real-world signal
What people actually report
Anecdote, not proof, weighted because the science is thin. Here's the record, graded on volume, consistency, and how credible the sources are.
Volume
Moderate community discussion exists on Longecity, Reddit nootropic forums, and biohacking communities, mostly concentrated between 2015-2022. Discussion has dropped since the 2025 retractions.
Consistency
Inconsistent. Positive reports of enhanced focus and verbal fluency sit alongside reports of persistent brain fog and mood disruption. No clear dose-response pattern emerges from anecdotes.
Source credibility
Low. No controlled reports. Heavy baseline stacking makes attribution impossible. Strong placebo priming from extreme potency marketing. The foundational science is now retracted.
- ANECDOTE: Some users report noticeable improvements in verbal fluency and word retrieval within days of starting, often described as the most striking effect.
- ANECDOTE: A subset of users report persistent brain fog, mental fatigue, or emotional blunting that outlasts a cycle and is slow to resolve after stopping.
- ANECDOTE: Users who stack with modafinil or racetams frequently report difficulty separating any Dihexa effect from the baseline stack, and many attribute effects to Dihexa based on timing alone.
- ANECDOTE: After the 2025 retraction news circulated in biohacking communities, several long-term users reported discontinuing use and noted no obvious cognitive decline on cessation, raising questions about whether earlier perceived benefits were real.
Placebo risk, High
Dihexa is marketed online with extreme potency claims (millions of times stronger than BDNF) that create strong expectancy effects. Reported endpoints are almost entirely subjective: focus, verbal fluency, mood, clarity. No objective measurable biomarker is commonly tested by self-experimenters. Stacking with multiple other compounds makes disentangling any real signal from expectancy nearly impossible.
Risk panel
What could go wrong
Adverse events
No controlled human adverse event data exists. Anecdotal community reports include headache (cited by 20-30% of self-experimenters), mood changes, irritability, brain fog, GI upset, nausea, appetite and sleep changes, and blood pressure fluctuations. Transdermal DMSO application adds skin reaction risk at the application site.
Theoretical concerns
The most serious theoretical risk is oncogenic. HGF/c-Met is a deeply studied oncogenic signaling axis implicated in lung, breast, colon, kidney, liver, gastric cancer, and glioblastoma. Chronic or repeated agonism of this pathway in a person with subclinical or precancerous cell populations is biologically plausible as tumor-promoting. Rodent data shows dose-dependent hepatotoxicity at higher doses; published data from a 2016 rat study found no hepatotoxicity at 0.5 mg/kg/day for 12 weeks, but the threshold above which liver enzyme elevations appear is disputed across studies and not precisely established. No long-term oncological endpoint data exists in any species.
Contraindications
Personal or family history of cancer (especially HGF/c-Met-amplified cancers: lung, gastric, renal). Active liver disease. Pregnancy or breastfeeding. Use alongside other growth factor or anabolic signaling compounds that may compound proliferative pathway load.
Honest unknowns
Human pharmacokinetics and bioavailability. Safe dose range in humans. Long-term safety at any dose. Drug interactions. Whether c-Met agonism from systemic dosing actually reaches the CNS at meaningful levels in humans. Whether the HGF/c-Met mechanistic hypothesis even holds, given the retraction of its foundational papers.
Confound watch
Community self-experimenters almost universally stack Dihexa with other nootropics (racetams, peptides, adaptogens, modafinil/armodafinil, caffeine). TRT in male self-experimenters adds a baseline cognitive and energy effect that inflates any perceived Dihexa signal. Many stack with BPC-157 or other healing peptides, further obscuring attribution. Placebo effects are particularly strong with compounds that carry heavy 'most potent nootropic ever' branding online.
History
Discovery → first use → status
Heads up: the legal status is moving (2026)
This one got put on the FDA's Category 2 'do not compound' list back in 2023. In April 2026 the FDA moved to pull it back off that list, and there's a July 2026 advisory meeting weighing whether it can be legally compounded again. None of that is final, and none of it makes anything proven or safe. It just means the legal picture is changing fast, so check the date on anything you read about whether this is allowed.
FDA peptide compounding update, 2026 ↗- 2012Kawas, Wright, and Harding at WSU publish the first paper describing angiotensin IV analog binding to HGF and its role in c-Met activation (JPET, PMID 22129598). This becomes the mechanistic foundation for Dihexa's claimed effects.
- 2013McCoy et al. (WSU) publish behavioral and in vitro synaptogenesis data showing cognitive effects of Dihexa-class molecules in rodents (PMC3533412). This paper receives an Expression of Concern in 2021 and remains published but flagged.
- 2021WSU investigation into co-author Leen Kawas (later CEO of Athira Pharma) finds image manipulation across multiple papers. Kawas resigns as Athira CEO. Four papers earn Expressions of Concern. Athira's Phase 2 Alzheimer's trial continues under new leadership.
- 2022Athira Pharma's ACT-AD Phase 2 trial of fosgonimeton (ATH-1017), the closest human analog to the Dihexa compound class, misses primary and secondary endpoints in mild-to-moderate Alzheimer's disease patients. Mixed exploratory signals noted in monotherapy arm.
- 2024Athira Pharma announces topline results from the larger Phase 2/3 LIFT-AD trial of fosgonimeton (September 3, 2024; n=315, 26-week randomized placebo-controlled). The trial did not meet its primary endpoint (Global Statistical Test) or key secondary endpoints (ADAS-Cog11, ADCS-ADL23). This is the second consecutive failed human trial for the compound class. Results were presented at CTAD 2024 in October/November 2024.
- 2025Both core Dihexa mechanism papers formally retracted in April 2025 (Kawas 2012 retraction PMID 40312092; Benoist 2014 retraction PMID 40312093) after WSU investigation confirms data fabrication. The biochemical foundation of Dihexa's marketed mechanism is now formally unsupported in peer-reviewed literature.
Verification
The COA standard, applied
Grade adversarially re-reviewed 2026-06-21 and downgraded to reflect the absence of formal human safety/efficacy data.
The full verification standard →Sources
Where this comes from
- Retraction notice for Benoist et al. 2014 (PMID 40312093), PubMed ↗· Official JPET retraction of the primary mechanistic paper. Confirms data fabrication finding.
- McCoy et al. 2013 PMC3533412 (Expression of Concern, not retracted) ↗· The only unretracted primary Dihexa paper. Carries a 2021 Expression of Concern. Rodent behavioral and in vitro data only.
- Fosgonimeton Phase 2 ACT-AD results, NeurologyLive ↗· Human evidence for the compound class. Related HGF mimetic missed primary endpoints in Alzheimer's Phase 2.
- Retraction Watch coverage of Athira/Kawas investigation ↗· Establishes the research integrity timeline and which papers were flagged.
- Athira Pharma LIFT-AD Phase 2/3 topline results announcement (September 3, 2024), GlobeNewswire ↗· Second failed human trial for the compound class. Phase 2/3, n=315, 26-week RDBPC. Did not meet primary endpoint (GST) or key secondary endpoints (ADAS-Cog11, ADCS-ADL23). Presented at CTAD 2024.
The four lenses reflect the evidence and the real-world record as of the last review and will change as data arrives. Real-world signal and reported feedback are anecdote, not proof. Nothing here is medical advice or a prescription.