HGH Fragment 176-191 and AOD-9604: One Residue Apart

For laboratory research use only. Not for human or veterinary use.

HGH Fragment 176-191 and AOD-9604 are sold side by side, usually described in the same words, and often treated as two names for one thing. They are close: the same length, the same fifteen residues at the back, the same internal disulfide bond. But as defined, they differ at one position, the very first residue, and that difference shows up as 16 mass units on a certificate. This guide sets out what each name means, where the research came from, what has and has not been measured, and how to tell which one a batch actually is.

Identity#

The masses above are our own calculation from the sequence, with the disulfide bond formed. The cysteines at positions 7 and 14 correspond to Cys182 and Cys189 of growth hormone, which are bonded to each other in the intact hormone.

What “176-191” actually means#

Human growth hormone is a single chain of 191 amino acids. Number them from the front, and residues 176 to 191 are the last sixteen: the C-terminal tail. In the natural hormone, residue 176 is phenylalanine. So “Fragment 176-191”, read literally, is Phe-Leu-Arg-…-Gly-Phe.

The original research did not use that piece. Work at Monash University in the 1990s used residues 177 to 191, fifteen residues long. AOD-9604 is that fifteen-residue piece with a tyrosine added to the front, which is how anti-doping chemists describe it. Because the added tyrosine sits exactly where phenylalanine sits in the hormone, AOD-9604 comes out the same length as “176-191” and differs from it only at position one.

The difference between the two residues is one hydroxyl group on the aromatic ring: tyrosine has it, phenylalanine does not. That is one oxygen atom, which is why the two masses sit 16 apart.

Why the names get blurred#

In practice the two names are used loosely, and not only by sellers. A 2026 review of growth hormone-axis peptides sold as research compounds lists AOD9604 under the label “176-191”. A product called Fragment 176-191 may therefore be the tyrosine sequence, the phenylalanine sequence, or simply AOD-9604 under another name.

The name on the label settles nothing. The sequence and the mass do:

• A sequence starting Tyr (Y) is AOD-9604’s sequence, whatever the product is called.
• A sequence starting Phe (F) is the stretch exactly as it appears in growth hormone.
• A sequence starting Leu (L) is the fifteen-residue 177-191 piece from the early papers, with nothing added.

Where it came from#

Interest in growth hormone’s tail goes back to the 1970s, when Frank Ng and J. Bornstein synthesised pieces of it to find which part of the hormone affects glucose handling. In the 1990s, Ng’s laboratory at Monash University turned to fat metabolism.

• 1978. Six synthetic pieces of the tail, among them 176-191 and 177-191, were tested in rats. Both of those produced a short-lived rise in blood glucose and a more sustained rise in insulin. Shorter pieces, from 179 onwards, did nothing measurable.
• 1993. Synthetic 177-191 reduced fat synthesis (lipogenesis) in rat fat tissue to the same degree as the intact hormone. In the same work it showed no significant effect on the breakdown of stored fat (lipolysis), measured as glycerol release.
• 1994. Given over a long period to ob/ob mice, a strain that lays down excess fat, 177-191 reduced cumulative body weight gain and fat tissue mass, and inhibited lipogenesis in that tissue.
• 2000. The tyrosine-extended analogue, now called AOD9604, was given by mouth to Zucker rats for 19 days. Their body weight gain was less than half that of controls, and their fat tissue showed raised lipolytic activity. Unlike intact growth hormone, it showed no adverse effect on insulin sensitivity, measured by glucose clamp.
• 2001. In 14-day studies in ob/ob and lean mice, AOD9604 reduced body weight gain, raised fat oxidation and raised plasma glycerol. Unlike growth hormone, it did not raise blood glucose or reduce insulin secretion. It did not compete for the growth hormone receptor, and did not drive cell proliferation in a receptor-based assay.
• 2001. A companion study in mice lacking the β3-adrenergic receptor found the long-term effect absent in those mice, although an acute rise in energy expenditure remained. The authors concluded the effect was not mediated directly through that receptor, though AOD9604 did increase its expression.

Two points are worth holding on to. The animal findings are consistent with each other, and they come largely from one laboratory and its collaborators. And the claim usually repeated in listings, that the fragment acts on fat without the glucose effects of the whole hormone, rests on the later rodent studies of AOD9604. The 1978 work, which tested 176-191 itself, found a short-lived glucose rise, so that claim should not be carried over from one sequence to the other without checking.

What has been tested in people#

Metabolic Pharmaceuticals, a Melbourne company, took AOD9604 into human trials. A 2004 drug-development profile records phase IIa trials under way by February 2002. The results of the later, larger trials were mostly reported by the company rather than in papers indexed on PubMed, so we do not summarise them here. What can be said plainly is that AOD-9604 is not a licensed medicine anywhere.

We have found no published human study of the phenylalanine sequence at all. For a wider view of how thin the human data is across this group of compounds, the 2026 review cited below grades each one by the quality of its evidence and lists the adverse effects reported with them.

The cartilage study#

A newer line of interest comes from a single 2015 study in rabbits. AOD9604, alone and with hyaluronic acid, was given into the knee joint in a laboratory model of cartilage damage. Cartilage was scored under the microscope and by appearance, and lameness was recorded. The groups receiving AOD9604 scored better than those receiving saline, and the combination with hyaluronic acid scored best. It is one animal study, from one group, and has not been followed by human data.

Anti-doping status#

AOD9604 is prohibited by the World Anti-Doping Agency. Anti-doping laboratories have published a urine test for it and identified its breakdown products, including a stable metabolite, CRSVEGSCG, that extends the window of detection. Vials of it have been identified among seized products in the United States and in Belgium. Anyone subject to anti-doping testing should not handle it. As with ipamorelin and AICAR, this is a plain fact about the compound and belongs on the page.

What to check on the certificate#

• The mass decides which one it is. AOD-9604 sits at 1815.08 (monoisotopic 1813.86). The phenylalanine sequence sits at 1799.08 (1797.87). The fifteen-residue 177-191 piece, with nothing at position one, sits at 1651.91. A certificate that names one and reports the mass of another is describing a different peptide.
• What the spectrum shows. A peptide this size usually appears as multiply charged ions. For AOD-9604, expect the doubly charged ion near 907.9 and the triply charged near 605.6. For the phenylalanine sequence, near 899.9 and 600.3.
• The disulfide. If the bond between the two cysteines has not formed, the mass is 2 units higher (about 1817.1 for AOD-9604). A certificate should report the bonded form.
• The sequence, printed. Check the first residue: Tyr or Phe. A certificate that gives only a name and a purity figure cannot tell you which you have.
• Purity, with the method named, measured on that batch.
• Net peptide content and counter-ion. A peptide this size carries a meaningful share of counter-ion, usually acetate, and water. Net peptide content is how much of the vial is peptide, and it is not the same number as purity.

Ask about the documentation for the batch we would ship before you order. See also how to read a COA, how to verify one and what a purity figure means.

Handling and storage#

Standard peptide handling applies. Store the sealed lyophilised vial cold, dry and out of light, and let it reach room temperature before opening. Reconstitute by running bacteriostatic or sterile water down the vial wall rather than onto the powder, and swirl rather than shake. Once in solution, keep it refrigerated and use it within its working window. The reconstitution guide, solvent guide and storage guide cover the detail.

What Pioneer supplies#

We list the two as separate products. AOD-9604 is stocked in a 5mg vial, with 2mg and 10mg made to order. HGH Fragment 176-191 is made to order in five sizes from 2mg to 15mg, in one to two weeks. Ask for the documentation for the batch we would ship: the mass on a certificate is what tells you which sequence a batch is.

Quality comes first#

Two products that differ by one oxygen atom will never be told apart by their labels. The only reliable way to know which one a vial holds is the mass on the certificate for that batch. Ask about the documentation for the batch we would ship before you order.

Sources#

Each entry links to its PubMed record, where the title and abstract can be read. The descriptions are ours: they say what each paper examined, not what it is claimed to show. Records checked on PubMed on 29 October 2026.

1. Ng FM, Bornstein J (1978). Am J Physiol 234(5):E521–6. Six synthetic pieces of the growth hormone tail, including 176–191 and 177–191, tested in rats for effects on blood glucose, insulin and insulin sensitivity. PubMed 645904
2. Wu Z, Ng FM (1993). Biochem Mol Biol Int 30(1):187–96. Synthetic 177–191 in rat fat tissue, measuring fat synthesis against the intact hormone and fat breakdown as glycerol release; no significant effect on the latter. PubMed 8358331
3. Natera SH, Jiang WJ, Ng FM (1994). Biochem Mol Biol Int 33(5):1011–21. Long-term study of synthetic 177–191 in ob/ob mice, measuring cumulative body weight gain, fat tissue mass and fat synthesis. PubMed 7987248
4. Ng FM, Sun J, Sharma L, et al. (2000). Horm Res 53(6):274–8. AOD9604 given by mouth to Zucker rats for 19 days: body weight gain, lipolytic activity of fat tissue, and insulin sensitivity by glucose clamp. PubMed 11146367
5. Heffernan MA, Thorburn AW, Fam B, et al. (2001). Int J Obes Relat Metab Disord 25(10):1442–9. Growth hormone and AOD9604 compared over 14 days in ob/ob and lean mice, with glucose, insulin, fat oxidation, receptor binding and cell proliferation assays. PubMed 11673763
6. Heffernan M, Summers RJ, Thorburn A, et al. (2001). Endocrinology 142(12):5182–9. The same comparison in mice lacking the β3-adrenergic receptor, testing whether that receptor carries the effect. PubMed 11713213
7. Wilding J (2004). Curr Opin Investig Drugs 5(4):436–40. Drug-development profile of AOD-9604 at Metabolic Pharmaceuticals, recording phase IIa human trials under way by February 2002. PubMed 15134286
8. Kwon DR, Park GY (2015). Ann Clin Lab Sci 45(4):426–32. Rabbit study of AOD9604, alone and with hyaluronic acid, given into the knee joint in a laboratory model of cartilage damage; cartilage scores and lameness recorded. PubMed 26275694
9. Vanhee C, Moens G, Deconinck E, et al. (2014). Drug Test Anal 6(9):964–8. Case report from the Belgian public health institute identifying AOD9604 in seized preparations of unknown content. PubMed 24976118
10. Cox HD, Smeal SJ, Hughes CM, et al. (2015). Drug Test Anal 7(1):31–8. Anti-doping laboratory method for detecting AOD9604 in urine, describing it as residues 177–191 with an added N-terminal tyrosine, and identifying its breakdown products. PubMed 25208511
11. Dominikowski A, Rękoś Z, Olejarz M, et al. (2026). Front Endocrinol (Lausanne) 17:1822475. Review of growth hormone-axis peptides sold as research compounds, grading the human evidence for each and listing the adverse effects reported with them. PubMed 42395176

Both compounds, in our catalogue#

• AOD-9604 — 5mg in stock; 2mg and 10mg made to order
• HGH Fragment 176-191 — made to order, 2mg to 15mg

Pioneer Research Peptides — UK supplier of research peptides for laboratory use. Ask about batch documentation before you order.

For laboratory research use only — not for human consumption. 18+.