What isDihexaFDA Status, Evidence and Risks (2026)
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Off FDA's Category 2 safety-risk list since Apr 2026. FDA's advisory panel is expected to review it before the end of Feb 2027, no date set. Not on the 503A bulks list. Not approved by FDA for any use. Source: FDA, Category 2 page current as of Apr 22, 2026 1, and 503A page current as of May 14, 2026 2.
Part of the Sommar Peptide Guide. Dihexa gets sold online as a memory peptide. Every memory result we found came from rats. FDA found zero human exposure data. Here is what that leaves.
What dihexa is
Dihexa (also called PNB-0408, sold as dihexa acetate) is a lab-made compound built from angiotensin IV, a small fragment of a blood pressure hormone 6,7.
Washington State University researchers changed that fragment so it would last longer in the body and cross from the blood into the brain. They reported the result in 2013: an oral compound that crossed into the brain in rats. They named it dihexa 6.
The proposed mechanism runs through HGF (hepatocyte growth factor) and its receptor, c-Met. Dihexa binds HGF and boosts its signal through c-Met, per the lab's work as summarized by the Alzheimer's Drug Discovery Foundation (ADDF) 7. That same HGF/c-Met system is where the cancer question comes from. More below.
Where FDA stands
- Apr 15, 2026: FDA said it would remove 12 peptides from Category 2 after their nominators withdrew them. Dihexa acetate was one 3.
- Apr 22, 2026: FDA's page moves dihexa to its table of withdrawn nominations. Its safety concerns stay listed 1.
- Today: not on the 503A bulks list, the list a pharmacy needs to compound a substance that is not part of an approved drug 2. Not approved by FDA for any use. Coming off Category 2 approved nothing. Are Peptides Legal? explains why.
- Before end of Feb 2027: a second Pharmacy Compounding Advisory Committee meeting is expected to take up dihexa and four other peptides. FDA has not set a date 4. Any vote would be advice only.
Not in the HHS policy. On Oct 28, 2026, HHS filed an interim enforcement discretion policy covering six peptides: BPC-157, TB-500, MOTS-c, epitalon, semax and KPV 5. Dihexa is not one of them and keeps its prior status, as of Oct 29, 2026. The FDA Peptide Tracker logs every change.
What the research shows
Evidence type: rats and cells. ADDF found no published human studies of dihexa, as of its Aug 2021 report 7.
| Claim | What was tested | What it found |
|---|---|---|
| Restores memory | Rats given scopolamine, a drug that impairs memory, then a water maze 6,7 | Dihexa reversed the deficit |
| Helps aging brains | 24-month-old rats, oral dihexa 7 | Better maze scores, with variable results |
| Boosts healthy memory | Healthy rats 7 | No improvement |
| Grows brain connections | Rat neurons in a dish 7 | More dendritic spines, the contact points between neurons |
Rats with a chemically induced deficit improved. Healthy rats did not. No study showed any of this in a person.
The mechanism paper carries a warning. The 2014 paper that tied dihexa's effects to HGF/c-Met 8 now has an expression of concern from its journal. The editors cited "possible image manipulation" and said they were waiting on an inquiry by Washington State University 9.
Fosgonimeton is a different drug
Fosgonimeton (ATH-1017) is the name you'll see next to dihexa in headlines. It is a separate molecule, a prodrug that the body converts to an active form, developed by Athira as a once-daily injection 10. Alzforum says it "may be related" to dihexa and came out of the same university work 10. Wikipedia calls it a phosphate prodrug of dihexa 13. Either way, its trials tested fosgonimeton. They did not test dihexa.
How those trials went:
- ACT-AD, 2022: 77 people with Alzheimer's. Missed its primary goal 10.
- Parkinson's and Lewy body dementia, Dec 2023: missed its primary goal. Stopped enrolling at 28 people 10.
- LIFT-AD, Sept 3, 2024: 312 people with mild to moderate Alzheimer's. Missed its primary goal (p=0.70) and its key secondary goals for memory and daily function at 26 weeks 11.
- Aug 2025: Athira paused further development of fosgonimeton 12.
We found no newer fosgonimeton results.
Side effects and FDA's concerns
FDA's stated concerns, from its Category 2 page 1:
- No human data. FDA "has not identified any human exposure data on drug products containing dihexa acetate administered via any route of administration."
- Harm unknown. FDA "lacks important information regarding any safety issues raised by dihexa acetate, including whether it would cause harm if administered to humans."
So no one can list dihexa side effects in people. Nobody has published them.
The cancer question. c-Met and HGF are often overactive in cancer cells, and that overactivity tracks with spread and worse outcomes 7. ADDF's read: "Theoretically, dihexa via activation of HGF and c-Met could promote tumorigenesis and cancer progression" 7. Theoretical means untested. No study has looked at dihexa's long-term effect on tumors 7. Fosgonimeton trials excluded people with a history of malignant tumors 7.
Other gaps, per ADDF 7:
- No long-term safety studies, in animals or people.
- Human half-life unknown. In rats it was about 12.7 days after an IV dose.
- Drug interactions never studied.
The closest human signal belongs to the other drug. In LIFT-AD, fosgonimeton caused more adverse events than placebo, mainly injection site reactions. The company called it "generally well tolerated" 11. That tells you about fosgonimeton, not dihexa.
Why it's sold online anyway
A 2013 university press release claimed dihexa was seven orders of magnitude (10 million times) more potent than BDNF, a brain growth protein. ADDF notes the paper never compared the two directly 7. That line still travels.
ADDF found no ongoing dihexa trials on ClinicalTrials.gov, and noted some private clinics may offer it anyway 7. Online sellers often label it "research use only." That label is the seller saying the product is not made for people.
What those products skip:
- A prescriber.
- Any quality check for human use.
Prescription vs Research Peptides has more.
Other Shelf 3 pages: semax, the brain peptide that did make the HHS policy, and DSIP, the sleep peptide FDA's panel voted down.
Asked a lot.
The sources.
- FDA. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (content current as of Apr 22, 2026). Read it
- FDA. Bulk Drug Substances Used in Compounding Under Section 503A of the FD&C Act (content current as of May 14, 2026). Read it
- Frier Levitt. FDA Peptides "Do Not Compound" List Update (Apr 16, 2026). Read it
- Holland & Knight. Peptides at a Crossroads: What Wellness Providers Need to Know (Oct 16, 2026). Read it
- HHS. Enforcement Discretion Policy Regarding 503A Compounding Using Certain Peptide Bulk Drug Substances. Docket HHS-OASH-2026-0496, FR Doc 2026-22192 (filed for public inspection Oct 28, 2026; scheduled to publish in the Federal Register Oct 30, 2026). Read it
- McCoy AT, Benoist CC, Wright JW, et al. Evaluation of metabolically stabilized angiotensin IV analogs as procognitive/antidementia agents. J Pharmacol Exp Ther. 2013;344(1):141-154. doi:10.1124/jpet.112.199497. Read it
- Alzheimer's Drug Discovery Foundation. Cognitive Vitality report: Dihexa (last updated Aug 13, 2021). Read it
- Benoist CC, Kawas LH, Zhu M, et al. J Pharmacol Exp Ther. 2014;351(2):390-402 (Alzforum record, marked expression of concern). Read it
- J Pharmacol Exp Ther. Expression of Concern: Benoist CC et al. (2014), doi:10.1124/jpet.114.218735. J Pharmacol Exp Ther. 378(3):311. Read it
- Alzforum. Therapeutics: Fosgonimeton (last updated Sept 10, 2024). Read it
- Athira Pharma. Topline results from Phase 2/3 LIFT-AD clinical trial of fosgonimeton (Sept 3, 2024), SEC exhibit 99.1. Read it
- Athira Pharma. Second quarter 2025 financial results and business update (Aug 7, 2025). Read it
- Wikipedia. Dihexa (second source only, for the prodrug description). Read it
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