# Dihexa Dihexa is in limbo: it is not approved, and it is on neither FDA list for compounding. No pharmacy may lawfully make it. The evidence grade is animal-only: it helped memory in some rat and mouse studies. FDA found no data on any person given it. Status checked: 2026-10-25. Last verified: 2026-10-26. Primary source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks This page has not been individually reviewed by a clinician. Information, not medical advice. | Fact | Value | Tier | Checked | Source | |---|---|---|---|---| | Also called | PNB-0408, N-hexanoic-Tyr-Ile-(6)-amino hexanoic amide | peer-reviewed | 2026-10-25 | [source](https://pubmed.ncbi.nlm.nih.gov/38489193/) | | Class | neuro-and-cognitive | peer-reviewed | 2026-10-25 | [source](https://pubmed.ncbi.nlm.nih.gov/23055539/) | | Regulatory status | limbo | primary | 2026-10-25 | [source](https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks) | | Status source read | 2026-10-25 | primary | 2026-10-25 | [source](https://www.fda.gov/media/94155/download) | | Evidence grade | animal-only | our assessment | 2026-10-25 | [source](https://peptideindex.ai/methodology#evidence-grade) | ## Name Dihexa Source: https://pubmed.ncbi.nlm.nih.gov/25649658/ ## Summary A small lab-made molecule built from a piece of angiotensin IV, a hormone fragment. It was tested for memory in rats and mice. Source: https://pubmed.ncbi.nlm.nih.gov/23055539/ ## Short answer Dihexa is in limbo: it is not approved, and it is on neither FDA list for compounding. No pharmacy may lawfully make it. The evidence grade is animal-only: it helped memory in some rat and mouse studies. FDA found no data on any person given it. Source: https://peptideindex.ai/methodology#short-answer ## Known risks - FDA found no data on people exposed to Dihexa acetate by any route [^1]. - FDA says it does not know enough about Dihexa to tell whether it would harm people [^1]. Source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks ## What nobody knows yet - Nobody knows whether Dihexa does anything in people. FDA found no data on any person given it [^1]. - How Dihexa acts in the body is not settled. The study that tied it to a growth signal called HGF was retracted [^10] [^11]. - The journal raised a concern in 2021 about the 2013 rat study that first described Dihexa [^8] [^9]. - Results differ by disease model. Dihexa did not protect rats in a model of Huntington's disease [^13]. - Dihexa is said to boost a signal that makes cells divide and move [^17]. The studies cited here did not look at whether that feeds unwanted growth. - FDA has not set a date for its committee to meet on Dihexa. Its notice does not say which use the committee will review [^4]. Source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks ## What it is Dihexa is a small lab-made molecule [^17]. Scientists built it from a short piece of angiotensin IV, a fragment of a hormone [^8]. They changed that piece so it would last longer in the body and pass from the blood into the brain [^8]. Its full chemical name is N-hexanoic-Tyr-Ile-(6)-amino hexanoic amide, and one study calls it PNB-0408 [^13]. Its makers tested it as a possible treatment for memory loss, such as in Alzheimer's disease [^8] [^17]. FDA calls the substance Dihexa acetate [^1]. FDA has found no data on any person given a drug containing it [^1]. Source: https://pubmed.ncbi.nlm.nih.gov/23055539/ ## Where it stands legally Dihexa is in limbo: FDA lists Dihexa acetate among the Category 2 substances whose nominations were withdrawn, and it has not added it to Category 1 [^1] [^2]. That is not approval, and it does not make compounding lawful. Checked 25 October 2026. Category 2 is FDA's list of substances that may raise significant safety risks. Category 1 is the list of substances under review that pharmacies may use while FDA decides [^3]. In April 2026, the groups that nominated Dihexa acetate withdrew, so it came off Category 2 [^1] [^5]. Taking a substance off Category 2 does not by itself let pharmacies use it [^5] [^6]. FDA says its Pharmacy Compounding Advisory Committee will discuss Dihexa acetate at a meeting before the end of February 2027 [^4] [^7]. FDA has posted no date for that meeting and no review of Dihexa for it [^4]. No public comment docket was open for that meeting when a trade group reported on it [^18]. The committee gives advice only [^5]. FDA decides by writing a rule [^6]. Until FDA acts, a pharmacy may not use Dihexa under the federal compounding law [^3] [^6]. Source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks ## What the evidence shows The evidence grade is animal-only: every study we found tested Dihexa in rats, mice, fish or cells [^16]. FDA found no data on any person given Dihexa [^1]. A result in an animal does not show what happens in people. Memory: in a 2013 study, Dihexa helped rats with memory problems find their way in a water maze [^8]. It also helped aged rats with memory loss [^8]. In 2021, the journal posted a notice of concern about that study [^9]. In a 2021 study, Dihexa helped mice bred to have an Alzheimer's-like disease do better in the same maze [^12]. A 2018 review of animal studies found that angiotensin IV and related molecules, Dihexa among them, helped memory in eight of nine studies of memory loss [^16]. How it acts: a 2014 animal study proposed that Dihexa acts by boosting a growth signal called HGF [^10]. The journal retracted that study in 2025 [^11]. A 2015 review by two of the scientists who made Dihexa describes it the same way [^17]. That review came out before the retraction. Both of its authors also list a biotech company among their workplaces [^17]. Other uses: in rats with Huntington's-like damage, Dihexa did not protect them [^13]. In rats with a repaired leg nerve, walking improved when stem cells and Dihexa were put into a leg muscle [^14]. In young zebrafish, Dihexa protected hair cells like those of the inner ear from two antibiotics that can harm hearing [^15]. Source: https://pubmed.ncbi.nlm.nih.gov/29733881/ ## Legitimate ways to get it There is no legal way to get Dihexa in the US today [^1] [^2]. FDA has found no data on any person given a drug containing it [^1]. A pharmacy may use a substance with no official quality standard only if it is in an approved drug or on the federal list [^3]. Dihexa is not on that list, and FDA is still deciding whether to add it [^2] [^4]. Any open trial would appear in the trials block below, with the date the registry was last checked. Source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks ## How people are getting it anyway This section describes what happens and is not a recommendation. Groups once asked FDA to let pharmacies make Dihexa acetate, then withdrew that request [^1] [^3]. No pharmacy may lawfully make it now [^3] [^6]. We found no federal warning letter, import alert or court record that names Dihexa. So this page does not describe websites, clinics or other sellers for Dihexa. FDA has no data on what Dihexa does in people, by any route [^1]. Source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks ## Access routes Source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks ### None Detail: There is no legal route to Dihexa in the US today. FDA has found no human exposure data on any drug product containing it, and it is not on the list of substances pharmacies may use. Source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks ## Unofficial channels Source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks ### Compounding outside the rules What it is: Made by a pharmacy from bulk Dihexa acetate, a substance groups once nominated for compounding and then withdrew. Legal position: A pharmacy may compound with a substance that has no official standard and is in no approved drug only if it is on FDA's list. Dihexa acetate is not on that list. (source: https://www.fda.gov/drugs/human-drug-compounding/bulk-drug-substances-used-compounding-under-section-503a-fdc-act) Documented risks: - FDA found no data on people exposed to Dihexa acetate by any route. (source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks) - FDA says it does not know enough about Dihexa to tell whether it would harm people. (source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks) Enforcement: - 2026-04-22: FDA's Category 2 page, updated 22 April 2026, lists Dihexa acetate as a nomination withdrawn by its nominators, with its safety gaps. (source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks) - 2026-05-14: FDA's 503A category list, updated 14 May 2026, does not name Dihexa acetate in any category. (source: https://www.fda.gov/media/94155/download) Source: https://www.fda.gov/drugs/human-drug-compounding/bulk-drug-substances-used-compounding-under-section-503a-fdc-act ## Recruiting trials Snapshot date: 2026-10-25. A listing is not a recommendation. Trials have strict eligibility rules. Talk to your doctor and read the official record. None in this snapshot. Source: https://clinicaltrials.gov/api/v2/studies?query.intr=dihexa+OR+PNB-0408&filter.overallStatus=RECRUITING%2CNOT_YET_RECRUITING&pageSize=50&sort=StartDate%3Adesc&countTotal=true&fields=NCTId%2CBriefTitle%2COverallStatus%2CPhase%2CLeadSponsorName%2CStartDate%2CLocationCountry%2CLocationState ## Sources Source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks ### 1. FDA: bulk drug substances that may present significant safety risks, including those withdrawn from Category 2 Type: regulatory Tier: primary Source: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks ### 2. FDA: categories of bulk drug substances nominated under section 503A, list updated 14 May 2026 Type: regulatory Tier: primary Source: https://www.fda.gov/media/94155/download ### 3. FDA: bulk drug substances used in compounding under section 503A Type: regulatory Tier: primary Source: https://www.fda.gov/drugs/human-drug-compounding/bulk-drug-substances-used-compounding-under-section-503a-fdc-act ### 4. FDA: Pharmacy Compounding Advisory Committee meeting before the end of February 2027 Type: regulatory Tier: primary Source: https://www.fda.gov/advisory-committees/pharmacy-compounding-advisory-committee/meeting-pharmacy-compounding-advisory-committee ### 5. McDermott Will & Schulte: what the July 2026 committee votes on peptides mean Type: legal-analysis Tier: legal-analysis Source: https://www.mcdermottlaw.com/insights/bulk-list-bound-pcac-backs-majority-of-peptides-in-two-day-public-meeting/ ### 6. Goodwin: FDA signals a possible change in its stance on compounding some peptides Type: legal-analysis Tier: legal-analysis Source: https://www.goodwinlaw.com/en/insights/blogs/2026/05/fda-signals-potentially-evolving-stance-toward-compounding-of-certain-peptides ### 7. Sheppard Mullin: FDA pairs its peptide policy with action against unlawful sellers Type: legal-analysis Tier: legal-analysis Source: https://www.sheppard.com/insights/blogs/fda-balances-peptide-policy-with-enforcement-against-unlawful-peptide-sellers ### 8. Dihexa and memory in rats with memory loss and in aged rats, 2013 Type: animal Tier: peer-reviewed Source: https://pubmed.ncbi.nlm.nih.gov/23055539/ ### 9. Notice of concern about the 2013 Dihexa rat study, 2021 Type: reference Tier: peer-reviewed Source: https://pubmed.ncbi.nlm.nih.gov/34551989/ ### 10. Dihexa and the HGF growth signal, 2014, retracted Type: animal Tier: peer-reviewed Source: https://pubmed.ncbi.nlm.nih.gov/25187433/ ### 11. Retraction notice for the 2014 Dihexa study, 2025 Type: reference Tier: peer-reviewed Source: https://pubmed.ncbi.nlm.nih.gov/40312093/ ### 12. Dihexa and memory in mice with an Alzheimer's-like disease, 2021 Type: animal Tier: peer-reviewed Source: https://pubmed.ncbi.nlm.nih.gov/34827486/ ### 13. Dihexa in rats with Huntington's-like damage, 2024 Type: animal Tier: peer-reviewed Source: https://pubmed.ncbi.nlm.nih.gov/38489193/ ### 14. Dihexa with stem cells after leg nerve repair in rats, 2021 Type: animal Tier: peer-reviewed Source: https://pubmed.ncbi.nlm.nih.gov/34703584/ ### 15. Dihexa and hair cells like those of the inner ear in young zebrafish, 2015 Type: animal Tier: peer-reviewed Source: https://pubmed.ncbi.nlm.nih.gov/25674052/ ### 16. Systematic review: angiotensin IV, its analogs and memory in animal studies, 2018 Type: systematic-review Tier: peer-reviewed Source: https://pubmed.ncbi.nlm.nih.gov/29733881/ ### 17. Review: the brain HGF system as a target for Alzheimer's disease, 2015 Type: reference Tier: peer-reviewed Source: https://pubmed.ncbi.nlm.nih.gov/25649658/ ### 18. RAPS: FDA considers adding a dozen peptides to its compounding list Type: reference Tier: established-news Source: https://www.raps.org/resource/fda-considers-adding-a-dozen-peptides-to-its-bulk-drug-compounding-list.html Last verified: 2026-10-26. Sources: - https://clinicaltrials.gov/api/v2/studies?query.intr=dihexa+OR+PNB-0408&filter.overallStatus=RECRUITING%2CNOT_YET_RECRUITING&pageSize=50&sort=StartDate%3Adesc&countTotal=true&fields=NCTId%2CBriefTitle%2COverallStatus%2CPhase%2CLeadSponsorName%2CStartDate%2CLocationCountry%2CLocationState - https://peptideindex.ai/methodology#evidence-grade - https://peptideindex.ai/methodology#short-answer - https://pubmed.ncbi.nlm.nih.gov/23055539/ - https://pubmed.ncbi.nlm.nih.gov/25649658/ - https://pubmed.ncbi.nlm.nih.gov/29733881/ - https://pubmed.ncbi.nlm.nih.gov/38489193/ - https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks - https://www.fda.gov/media/94155/download [^1]: FDA: bulk drug substances that may present significant safety risks, including those withdrawn from Category 2 https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks [^2]: FDA: categories of bulk drug substances nominated under section 503A, list updated 14 May 2026 https://www.fda.gov/media/94155/download [^3]: FDA: bulk drug substances used in compounding under section 503A https://www.fda.gov/drugs/human-drug-compounding/bulk-drug-substances-used-compounding-under-section-503a-fdc-act [^4]: FDA: Pharmacy Compounding Advisory Committee meeting before the end of February 2027 https://www.fda.gov/advisory-committees/pharmacy-compounding-advisory-committee/meeting-pharmacy-compounding-advisory-committee [^5]: McDermott Will & Schulte: what the July 2026 committee votes on peptides mean https://www.mcdermottlaw.com/insights/bulk-list-bound-pcac-backs-majority-of-peptides-in-two-day-public-meeting/ [^6]: Goodwin: FDA signals a possible change in its stance on compounding some peptides https://www.goodwinlaw.com/en/insights/blogs/2026/05/fda-signals-potentially-evolving-stance-toward-compounding-of-certain-peptides [^7]: Sheppard Mullin: FDA pairs its peptide policy with action against unlawful sellers https://www.sheppard.com/insights/blogs/fda-balances-peptide-policy-with-enforcement-against-unlawful-peptide-sellers [^8]: Dihexa and memory in rats with memory loss and in aged rats, 2013 https://pubmed.ncbi.nlm.nih.gov/23055539/ [^9]: Notice of concern about the 2013 Dihexa rat study, 2021 https://pubmed.ncbi.nlm.nih.gov/34551989/ [^10]: Dihexa and the HGF growth signal, 2014, retracted https://pubmed.ncbi.nlm.nih.gov/25187433/ [^11]: Retraction notice for the 2014 Dihexa study, 2025 https://pubmed.ncbi.nlm.nih.gov/40312093/ [^12]: Dihexa and memory in mice with an Alzheimer's-like disease, 2021 https://pubmed.ncbi.nlm.nih.gov/34827486/ [^13]: Dihexa in rats with Huntington's-like damage, 2024 https://pubmed.ncbi.nlm.nih.gov/38489193/ [^14]: Dihexa with stem cells after leg nerve repair in rats, 2021 https://pubmed.ncbi.nlm.nih.gov/34703584/ [^15]: Dihexa and hair cells like those of the inner ear in young zebrafish, 2015 https://pubmed.ncbi.nlm.nih.gov/25674052/ [^16]: Systematic review: angiotensin IV, its analogs and memory in animal studies, 2018 https://pubmed.ncbi.nlm.nih.gov/29733881/ [^17]: Review: the brain HGF system as a target for Alzheimer's disease, 2015 https://pubmed.ncbi.nlm.nih.gov/25649658/ [^18]: RAPS: FDA considers adding a dozen peptides to its compounding list https://www.raps.org/resource/fda-considers-adding-a-dozen-peptides-to-its-bulk-drug-compounding-list.html