The second PCAC five: LL-37, GHK-Cu, dihexa, melanotan II and PEG-MGF

What the meeting decides, and when

Licensed pharmacies in the US may compound medicines from bulk drug substances that meet one of three conditions: the substance is part of an approved drug, it has a United States Pharmacopeia monograph, or it is on FDA's list of bulk substances for section 503A compounding, the '503A bulks list'. Most peptides sold through clinics meet none of these, which is why their compounding has been restricted. FDA's Pharmacy Compounding Advisory Committee (PCAC) advises the agency on which substances belong on the list.

In April 2026 FDA removed 12 peptides from Category 2, its list of substances raising significant safety risks, and said the committee would review them in two meetings ¹. The first, on July 23 and 24, 2026, covered seven: BPC-157, KPV, TB-500, MOTS-c, emideltide (DSIP), semax and epitalon. FDA's briefing documents proposed against adding every one of them, yet the committee voted to recommend 6 of the 7; only emideltide was voted down ². Our July PCAC hub records each vote and what has happened since.

The second meeting will discuss the remaining five: cathelicidin (LL-37), GHK-Cu, dihexa acetate, melanotan II and pegylated mechano growth factor (PEG-MGF). As of October 3, 2026, FDA's meeting page, last updated April 15, 2026, says only that the time and location will be scheduled in the coming months and that the meeting will happen before the end of February 2027 ¹. FDA says it intends to post briefing materials no later than two business days before the meeting ¹.

What each file will be judged on

FDA evaluates a substance for the 503A list against four criteria, balanced against each other: how well its physical and chemical properties are characterised; its safety; its effectiveness for the uses proposed; and its historical use in compounding. In July, FDA's briefings for all seven peptides found weaknesses on most of these, and the committee recommended six anyway, often by narrow margins ². That gap between the agency's analysis and the committee's votes is the most important thing to know going into the second meeting: the outcome is not predictable from the evidence alone.

What FDA has already published about the five is its risk statement for each, written when they sat in Category 2 or on the list of withdrawn nominations. Those statements are the starting point for any briefing ³:

Two of the five, dihexa and PEG-MGF, have no human exposure data at all in FDA's words. That is a weaker position than any of July's seven.

GHK-Cu: a cosmetic ingredient, reviewed as an injection

GHK-Cu is the best known of the five, and the only one with a large legal market: as a cosmetic ingredient in creams and serums. The review concerns it as a bulk substance for compounding, and FDA's risk statement concerns injectable routes specifically: possible immune reactions from aggregation and peptide-related impurities, and limited human data ³. Its human evidence is thin. The one small randomised trial on record, in 13 patients after laser resurfacing, found no difference on blinded measures, although patients rated their own skin better ⁴, and a 2025 review found a surprising absence of clinical studies of GHK-Cu itself ⁵. Most of its literature is cell and animal work, much of it from the group that discovered it. Our skin and hair hub grades it alongside other cosmetic peptides.

GHK-Cu may be the likeliest of the five to win a recommendation, because it has the longest history of human exposure, if mostly on the skin. But a recommendation for injectable compounding would rest on evidence gathered almost entirely from topical use and animals.

Melanotan II: the clearest safety record, and not a good one

Melanotan II is the only one of the five that has been given to people in published studies, which is also why it has the clearest record of harm. Its first human study, in three healthy men, produced darker skin in two, with spontaneous erections, nausea and sleepiness ⁶. It was never approved; its developer moved on to its metabolite, bremelanotide, which was approved for low sexual desire in premenopausal women. FDA's risk statement cites published case reports of melanoma, posterior reversible encephalopathy syndrome (a form of brain swelling), sympathomimetic toxidrome and priapism ³, and further reports link it to kidney infarction and kidney failure ⁷. Products sold online have been found under-strength and impure ⁸, and users combine it with sunbeds ⁹.

Its file will face a basic question about clinical need. It is sold for tanning and sexual function. Tanning is not a medical need, and an approved melanocortin drug already exists for the sexual-desire indication.

Cathelicidin (LL-37): a natural defence peptide with worrying animal signals

LL-37 is the only human member of the cathelicidin family, antimicrobial peptides made by immune and skin cells to kill bacteria, fungi and viruses. It is a natural part of the body, and there is a large literature on its role in infection, skin disease and cancer ¹⁰. But according to our entry it has never been tested as a treatment; its human studies measure it in blood and urine ¹¹. In mice, lacking it led to more urinary infections ¹².

FDA's risk statement goes beyond the usual immunogenicity concern: nonclinical research suggests detrimental effects on male reproduction, and that LL-37 can promote tumours in some tissues ³. In one cell study, LL-37 at concentrations reachable after vitamin D stimulation reduced the viability of bone-forming cells ¹³. For a substance sold to boost immunity and healing, a tumour-promotion signal is a serious obstacle.

Dihexa: no human data, and a retracted foundation

Dihexa is a small modified fragment of angiotensin IV sold as a 'cognitive enhancer'. FDA says it has not identified any human exposure data for dihexa by any route and lacks important information on whether it would cause harm ³. Its evidence is in rodents: in a mouse model of Alzheimer's disease it improved spatial learning ¹⁴, and in rats it was tested in nerve repair ¹⁵. More damaging, the 2014 paper that tied dihexa to the HGF/c-Met growth-factor pathway, the basis of most marketing claims about it, is listed on PubMed as retracted, as are two related papers from the same group, according to our entry ¹¹. A substance with no human data whose mechanism paper has been withdrawn starts its review from the weakest possible position.

PEG-MGF: a contested concept with no human exposure

PEG-MGF is the synthetic E-domain fragment of a splice variant of IGF-1, called mechano growth factor, with a polyethylene glycol chain attached to make it last longer. It is sold for muscle growth and recovery. FDA says it may pose a significant risk of immune reactions, has impurity and characterisation complexities, and that FDA has found no human exposure data by any route ³. The unpegylated fragment has been studied in cultured human muscle cells, where it extended the lifespan of satellite cells from young donors but not old ones ¹⁶, and the variant it comes from is more abundant in colorectal cancers than in normal colon tissue ¹⁷. According to our entry, whether the variant even produces a biologically active fragment in the body has been questioned by independent laboratories ¹¹.

What happens after the vote

A committee recommendation is advice, not a decision. For the July peptides, FDA must still decide whether to propose them for the 503A list and then complete rulemaking before pharmacies may compound them; as of our last check, none of the six recommended in July had moved to Category 1 on FDA's list of nominated substances ². The same will apply to the five in 2027. Until then, products sold online as LL-37, GHK-Cu injections, dihexa, melanotan II or PEG-MGF remain unapproved research chemicals of unknown quality, whatever the committee eventually says.

We will re-date this page when FDA sets a meeting date, posts briefing documents, or the committee votes. Our legal status checker shows each substance's status across six jurisdictions, and our regulatory tracker follows FDA's actions as they happen.

Frequently asked questions

When is the second PCAC peptide meeting?

As of October 3, 2026, FDA has not set a date. Its meeting page says the committee will meet before the end of February 2027 and that the time and location will be scheduled in the coming months.

Which peptides will the second PCAC review?

Cathelicidin (LL-37), GHK-Cu, dihexa acetate, melanotan II and pegylated mechano growth factor (PEG-MGF), for possible inclusion on the 503A bulks list.

Will GHK-Cu become legal to compound?

Not automatically. Even if the committee recommends it, FDA must then act and complete rulemaking. The review concerns GHK-Cu as a bulk substance, and FDA's risk statement addresses injectable routes.

Does a PCAC vote make a peptide legal?

No. The committee's votes are non-binding advice. In July 2026 it recommended 6 of 7 peptides, but none can be compounded from bulk until FDA completes its process.

Related on Grey Peptides

• July 2026 PCAC hub
• Regulatory tracker
• Legal Status Checker

Sources

1. FDA. Meeting of the Pharmacy Compounding Advisory Committee (February 2027): agenda and time and location 'will be scheduled in the coming months'. Content current as of April 15, 2026; read October 3, 2026. FDA
2. Grey Peptides July 2026 PCAC record (votes as reported by FDA Law Blog, McDermott and RAPS; FDA's briefing positions; FDA's 503A nominations list updated May 14, 2026, read September 25, 2026).
3. FDA. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (Category 2 and withdrawn nominations). Content current as of April 22, 2026; read October 3, 2026. FDA
4. Miller, T. R., et al. (2006). Effects of topical copper tripeptide complex on CO2 laser-resurfaced skin. Arch Facial Plast Surg, 8(4), 252-9. PMID: 16847171
5. Mortazavi, S. M., et al. (2025). Topically applied GHK as an anti-wrinkle peptide: Advantages, problems and prospective. Bioimpacts, 15, 30071. PMID: 39963574
6. Dorr, R. T., et al. (1996). Evaluation of melanotan-II, a superpotent cyclic melanotropic peptide in a pilot phase-I clinical study. Life Sci, 58(20), 1777-84. PMID: 8637402
7. Peters, B., et al. (2020). Melanotan II: a possible cause of renal infarction: review of the literature and case report. CEN Case Rep, 9(2), 159-161. PMID: 31953620
8. Breindahl, T., et al. (2015). Identification and characterization by LC-UV-MS/MS of melanotan II skin-tanning products sold illegally on the Internet. Drug Test Anal, 7(2), 164-72. PMID: 24771717
9. Gilhooley, E., et al. (2021). Melanotan II User Experience: A Qualitative Study of Online Discussion Forums. Dermatology, 237(6), 995-999. PMID: 34464955
10. Vandamme, D., et al. (2012). A comprehensive summary of LL-37, the factotum human cathelicidin peptide. Cell Immunol, 280(1), 22-35. PMID: 23246832
11. Grey Peptides encyclopedia entries for cathelicidin, dihexa and PEG-MGF (status and evidence notes). Read October 3, 2026.
12. Chromek, M., et al. (2006). The antimicrobial peptide cathelicidin protects the urinary tract against invasive bacterial infection. Nat Med, 12(6), 636-41. PMID: 16751768
13. Aidoukovitch, A., et al. (2024). Vitamin D triggers hCAP18/LL-37 production: Implications for LL-37-induced human osteoblast cytotoxicity. Biochem Biophys Res Commun, 712-713, 149962. PMID: 38642493
14. Sun, X., et al. (2021). AngIV-Analog Dihexa Rescues Cognitive Impairment and Recovers Memory in the APP/PS1 Mouse via the PI3K/AKT Signaling Pathway. Brain Sci, 11(11). PMID: 34827486
15. Weiss, J. B., et al. (2021). Stem cell, Granulocyte-Colony Stimulating Factor and/or Dihexa to promote limb function recovery in a rat sciatic nerve damage-repair model: Experimental animal studies. Ann Med Surg (Lond), 71, 102917. PMID: 34703584
16. Kandalla, P. K., et al. (2011). Mechano Growth Factor E peptide (MGF-E), derived from an isoform of IGF-1, activates human muscle progenitor cells and induces an increase in their fusion potential at different ages. Mech Ageing Dev, 132(4), 154-62. PMID: 21354439
17. Alagaratnam, S., et al. (2020). Increased expression of IGF-1Ec with increasing colonic polyp dysplasia and colorectal cancer. J Cancer Res Clin Oncol, 146(11), 2861-2870. PMID: 32772171

Educational information, not medical advice. Each dose in this guide names its source, an approved label or a published study. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose.