Peptides & growth hormone

HGH Fragment 176-191

Updated · 22 sources · Editorial policy

HGH Fragment 176-191 (also written “hGH 176–191”, “Frag 176-191” or “somatotropin 176–191”) is a synthetic 16-amino-acid peptide matching the last 16 building blocks of human growth hormone (hGH). It is sold online as a “fat-loss peptide” and is described in reviews of performance-enhancing drugs as a product promoted for fat metabolism (Coutinho et al., J Sports Med Phys Fitness 2026).

The name covers two slightly different peptides. The natural 176–191 segment of hGH starts with phenylalanine. The developed drug candidate AOD-9604 starts with tyrosine instead, and is also commonly labeled “hGH 176–191” (Dominikowski et al., Front Endocrinol 2026). The single most important fact: no human trial of the natural 176–191 peptide has been published. All human data under this name come from AOD-9604, which failed as an obesity drug. Neither peptide is an approved medicine, and both are banned in sport at all times.

This page summarizes what the early laboratory and animal studies, later reviews and regulators report. It is for education only and is not medical advice.

Property Detail
Class Synthetic peptide fragment of human growth hormone (C-terminal residues 176–191); research chemical
Structure 16 amino acids with one internal disulfide ring; C₇₈H₁₂₃N₂₃O₂₂S₂, 1799.1 g/mol (PubChem)
Relation to AOD-9604 Same length; AOD-9604 has tyrosine instead of phenylalanine at the first position (one extra oxygen atom)
Approval Never developed as a drug; not an approved medicine
Human studies None published for the natural peptide; human data under this name refer to AOD-9604
Half-life Not reported in humans or animals; the closely related AOD-9604 had a half-life of ≈3 min after IV injection in pigs
Key early finding In normal rats in 1978, it raised blood sugar briefly and plasma insulin for longer
US status Not approved; FDA’s compounding safety-risk list names AOD-9604 but not hGH 176–191 as a separate entry
WADA Prohibited at all times (S2.2.3, growth hormone fragments), named explicitly

What it is

Human growth hormone is a 191-amino-acid protein. Its last stretch, from position 176 to 191, contains two cysteines (positions 182 and 189) that are linked by a disulfide bond in the natural hormone (UniProt P01241). A synthetic copy of this stretch is hGH 176–191. PubChem lists it as “Somatotropin (176-191)” with the 7–14 disulfide ring, formula C₇₈H₁₂₃N₂₃O₂₂S₂ and molecular weight 1799.1 g/mol (PubChem CID 16131230).

Three closely related peptides appear in the literature and in product names:

Peptide Length How it differs
hGH 176–191 (natural) 16 residues Exact copy of the end of hGH; first residue is phenylalanine (UniProt)
hGH 177–191 15 residues Lacks the first residue; the form used in most 1990s fat-tissue work (Wu and Ng, 1993)
AOD-9604 (Tyr-hGH 177–191) 16 residues hGH 177–191 with tyrosine added in front; C₇₈H₁₂₃N₂₃O₂₃S₂, 1815.1 g/mol (PubChem)

Because AOD-9604 also spans 16 residues, reviews note that it is “sometimes labelled” hGH 176–191 (Dominikowski et al., 2026). The confusion reaches the research literature: a 2022 cell-culture paper titled “hGH fragment 176-191” modeled a sequence that begins with tyrosine, which is the AOD-9604 peptide (Habibullah et al., Drug Des Devel Ther 2022). A vial sold as “Fragment 176-191” may therefore contain either peptide, and the label alone does not show which. WADA lists “AOD-9604 and hGH 176-191” as two separate examples of growth hormone fragments.

The library has separate pages for AOD-9604, which covers the developer’s trials in detail, and for full-length HGH.

History

The C-terminal fragments of hGH were first made in the late 1970s by Ng, Bornstein and colleagues, who were studying why growth hormone raises blood sugar:

The natural 176–191 peptide itself was never taken into human development.

How it works in the body

Mechanism. No receptor for hGH 176–191 has been identified. For the tyrosine version, AOD-9604, mouse and cell studies showed that it does not compete with hGH for the growth hormone receptor and does not make receptor-carrying cells multiply (Heffernan et al., Int J Obes 2001). No equivalent receptor study of the natural 176–191 peptide was found.

Pharmacokinetics. No study has measured absorption, half-life or clearance of the natural 176–191 peptide in people or animals. The only related data are for AOD-9604, which had a half-life of about 3 minutes after IV injection in pigs and about 4 minutes in rat plasma in the lab (Moré and Kenley, J Endocrinol Metab 2014). A 2026 doping-control study found that hGH 176–191 broke down extensively in serum and plasma samples kept for one week at 4 °C or 22 °C, but stayed detectable in dried blood spots and in samples frozen at −20 °C for at least two months (Mazzarino et al., Analyst 2026). That describes sample stability in the lab, not how long the peptide lasts in the body.

What the research shows

Blood sugar and insulin in rats

The only published animal study of the natural 176–191 peptide that we found looked at blood sugar, not fat (Ng and Bornstein, 1978). In normal rats:

Fragment tested Effect
hGH 172–191, 176–191, 177–191, 178–191 Short-lived rise in blood glucose and a longer rise in plasma insulin
hGH 179–191, 180–191 No effect in the tests used
Active fragments at a single dose of 5 nmol/kg Reduced insulin sensitivity in IV insulin tolerance tests

These are effects in the direction of insulin resistance, the same direction as full-length growth hormone. A 1982 study described the mechanism of this hyperglycemic action of C-terminal peptides in more detail (Ma et al., Biochim Biophys Acta 1982).

“Does not affect blood sugar.” Product descriptions often say Fragment 176-191 burns fat without the blood-sugar effects of growth hormone. That claim comes from AOD-9604: in obese mice, AOD-9604 did not raise blood glucose or lower insulin secretion, unlike hGH (Heffernan et al., 2001), and the sponsor reported no negative effect on glucose tolerance in its human trials (Stier et al., J Endocrinol Metab 2013). The natural 176–191 peptide, in the only animal study that tested it, raised blood sugar and insulin in rats. The two peptides should not be assumed to behave the same.

Fat tissue (animal and lab data, mostly hGH 177–191)

The fat-loss reputation rests on work with the 15-residue hGH 177–191 and its tyrosine variants, not on the natural 176–191 peptide:

  • Rat fat tissue. Synthetic hGH 177–191 blocked fat formation (lipogenesis) in rat fat tissue as strongly as intact hGH. It had no significant effect on fat breakdown, measured as glycerol release (Wu and Ng, Biochem Mol Biol Int 1993).
  • Rat fat cells. hGH 177–191 reduced glucose uptake into fat cells from obese Zucker rats and was more potent than hGH at equal molar concentrations (Wijaya and Ng, Biochem Mol Biol Int 1993).
  • Obese mice. Long-term treatment with hGH 177–191 reduced cumulative weight gain and fat tissue mass in genetically obese mice (Natera et al., Biochem Mol Biol Int 1994).
  • Oral dosing in mice, human fat in the lab. The modified peptide AOD-9401, given by mouth for 30 days, slowed weight gain in obese mice (n = 10 treated vs 8 controls) from day 16 onward, without changing food intake. It also increased fat breakdown and reduced fat formation in fat tissue taken from obese rodents and humans and tested in the lab (Heffernan et al., 2000).

These were short studies in genetically obese rodents or in isolated tissue. They show a biological signal for the hGH 177–191 family, not an effect in people.

Human data

No randomized trial, pharmacokinetic study or case series of the natural hGH 176–191 peptide in people has been published. Reviews in 2026 describe the “Frag 176-191” and AOD-9604 class as experimental, with limited clinical evidence and poorly defined long-term risks (Coutinho et al., 2026; Dominikowski et al., 2026).

The human trials that are often quoted for “Fragment 176-191” were run with AOD-9604, by mouth or as single IV infusions. In the largest, a 24-week trial with 502 randomized participants, AOD-9604 failed to show a significant benefit on the primary weight-loss endpoint, and the review found no meaningful IGF-1 rise in human studies (Dominikowski et al., 2026). The sponsor’s trials used oral doses or single IV infusions. Details of all six are on the AOD-9604 page. None tested repeated injections under the skin, muscle gain, fat loss in lean people or athletic performance.

Other laboratory work

A 2022 study loaded a peptide labeled hGH fragment 176–191 together with the chemotherapy drug doxorubicin into nanoparticles and found greater killing of breast cancer cells in culture than with doxorubicin alone (Habibullah et al., 2022). This was a computer-modeling and cell-culture drug-delivery experiment, and, as noted above, the peptide modeled was the tyrosine (AOD-9604) version. It says nothing about effects in people.

Side effects and risks

No human safety data

Because the natural peptide has never been tested in people, its side effects, safe dose range and long-term risks are unknown. The sponsor described AOD-9604’s safety in its oral and single-dose IV trials as indistinguishable from placebo (Stier et al., 2013). That record cannot simply be transferred to a peptide with a different first amino acid, and it does not cover repeated injections.

Blood sugar and insulin

In the 1978 rat study, the natural 176–191 peptide briefly raised blood glucose and raised insulin, and the active fragments reduced insulin sensitivity (Ng and Bornstein, 1978). Whether this happens in people has not been studied. Reviews of performance-enhancing peptides list insulin resistance among the emerging risks of this drug group (Coutinho et al., 2026).

Immune reactions and product quality

  • Immunogenicity. FDA says compounded AOD-9604 “may pose significant risk for immunogenicity” (the risk of triggering an immune reaction) for certain routes of administration, and may have problems with peptide impurities (FDA, 2026). FDA has not published a separate assessment of hGH 176–191.
  • Unregulated supply. Products sold as “Frag 176-191” come from an unregulated market in which peptides are often mislabeled or contaminated (Coutinho et al., 2026). As described above, even the identity of the peptide (phenylalanine or tyrosine version) is not settled by the name on the label. We found no published laboratory analysis of products sold under this specific name.
  • WADA. “hGH 176-191” is named in class S2.2.3 of the 2026 Prohibited List, alongside AOD-9604, as an example of growth hormone fragments. All S2 substances are prohibited in and out of competition and are non-Specified Substances (WADA 2026 Prohibited List).
  • Detection. A 2026 doping-control method detects hGH 176–191 among 54 prohibited compounds in dried blood spots, serum and plasma, with detection limits of 0.05–1.25 ng/mL across the panel (Mazzarino et al., 2026).
  • United States. Not an approved drug. It is not a named anabolic steroid under 21 CFR 1308.13. FDA’s list of compounding substances that may present significant safety risks names AOD-9604 but does not list hGH 176–191 separately (FDA, 2026).

Key takeaways

  • One name, two peptides. The natural hGH 176–191 starts with phenylalanine; AOD-9604, also sold under this name, starts with tyrosine. Labels and even some papers mix them up.
  • No human studies of the natural peptide. Every human result quoted for “Fragment 176-191” comes from AOD-9604, which failed to produce significant weight loss in a 24-week trial.
  • The original rat data point the other way on blood sugar. In 1978 the natural 176–191 peptide raised blood glucose and insulin in normal rats. The “no blood sugar effect” claim comes from AOD-9604 studies.
  • The fat-loss evidence is animal and lab work. It mostly used the shorter hGH 177–191, which blocked fat formation in rat tissue but did not significantly increase fat breakdown.
  • Unknown kinetics and safety. No half-life, dose-response or safety data exist for the natural peptide in people, and product identity and purity are uncertain.
  • Banned in sport. WADA names hGH 176–191 under S2.2.3, prohibited at all times.

Sources

  1. Wade JD, Pullin CO, Ng FM, et al. The synthesis and hyperglycaemic activity of the amino acid sequence 172-191 of human growth hormone. Biochem Biophys Res Commun. 1977;78(2):827–832. PubMed.
  2. Ng FM, Bornstein J. Hyperglycemic action of synthetic C-terminal fragments of human growth hormone. Am J Physiol. 1978;234(5):E521–E526. PubMed.
  3. Wade JD, Ng FM, Bornstein J. Diabetogenic action of human growth hormone. Synthesis and activity of C-terminal fragments. Int J Pept Protein Res. 1979;13(2):195–200. PubMed.
  4. Ma GY, Macaulay SL, Maggs JA, et al. The mechanism of the hyperglycaemic action of synthetic peptides related to the C-terminal sequence of human growth hormone. Biochim Biophys Acta. 1982;716(3):400–409. PubMed.
  5. Wade JD, Ng FM, Bornstein J, et al. Effect of C-terminal chain shortening on the insulin-antagonistic activity of human growth hormone 177–191. Acta Endocrinol (Copenh). 1982;101(1):10–14. PubMed.
  6. Wu Z, Ng FM. Antilipogenic action of synthetic C-terminal sequence 177-191 of human growth hormone. Biochem Mol Biol Int. 1993;30(1):187–196. PubMed.
  7. Wijaya E, Ng FM. Effect of an antilipogenic fragment of human growth hormone on glucose transport in rat adipocytes. Biochem Mol Biol Int. 1993;31(3):543–552. PubMed.
  8. Natera SH, Jiang WJ, Ng FM. Reduction of cumulative body weight gain and adipose tissue mass in obese mice: response to chronic treatment with synthetic hGH 177-191 peptide. Biochem Mol Biol Int. 1994;33(5):1011–1021. PubMed.
  9. Heffernan MA, Jiang WJ, Thorburn AW, Ng FM. Effects of oral administration of a synthetic fragment of human growth hormone on lipid metabolism. Am J Physiol Endocrinol Metab. 2000;279(3):E501–E507. PubMed.
  10. Heffernan MA, Thorburn AW, Fam B, et al. Increase of fat oxidation and weight loss in obese mice caused by chronic treatment with human growth hormone or a modified C-terminal fragment. Int J Obes Relat Metab Disord. 2001;25(10):1442–1449. PubMed.
  11. Habibullah MM, Mohan S, Syed NK, et al. Human growth hormone fragment 176-191 peptide enhances the toxicity of doxorubicin-loaded chitosan nanoparticles against MCF-7 breast cancer cells. Drug Des Devel Ther. 2022;16:1963–1974. PubMed.
  12. Dominikowski A, Rękoś Z, Olejarz M, et al. The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration. Front Endocrinol (Lausanne). 2026;17:1822475. PubMed.
  13. Coutinho LFD, De Oliveira Neves LF, Camilo RP. A new era of doping? Use of peptide and peptide-analog drugs in recreational and professional sport and bodybuilding: a critical review. J Sports Med Phys Fitness. 2026;66(7):880–885. PubMed.
  14. Stier H, Vos E, Kenley D. Safety and tolerability of the hexadecapeptide AOD9604 in humans. J Endocrinol Metab. 2013;3(1-2):7–15. doi:10.4021/jem157w. Journal.
  15. Moré MI, Kenley D. Safety and metabolism of AOD9604, a novel nutraceutical ingredient for improved metabolic health. J Endocrinol Metab. 2014;4(3):64–77. doi:10.14740/jem213w. Journal.
  16. Mazzarino M, Colpaert T, Deventer K, Van Eenoo P. Rapid and harmonized analytical workflow for the determination of peptidic and non-peptidic doping agents in dried and liquid blood matrices. Analyst. 2026;151(15):4398–4413. PubMed.
  17. World Anti-Doping Agency. The 2026 Prohibited List. In effect January 1, 2026. WADA 2026 Prohibited List.
  18. Food and Drug Administration. Certain bulk drug substances for use in compounding that may present significant safety risks. FDA.
  19. Code of Federal Regulations. 21 CFR 1308.13, Schedule III. 21 CFR 1308.13.
  20. National Center for Biotechnology Information. PubChem compound summary for CID 16131230, Somatotropin (176-191). PubChem.
  21. National Center for Biotechnology Information. PubChem compound summary for CID 71300630, AOD-9604. PubChem.
  22. UniProt Consortium. P01241, Somatotropin (Homo sapiens). UniProt.