Fragment 176-191 research monograph — the hGH C-terminal fragment, its rodent lipid-metabolism record and its overlap with AOD-9604

"Fragment 176-191" ("HGH Frag 176-191") is a synthetic peptide named for residues 176–191 at the C-terminal end of human growth hormone (hGH), marketed for fat-metabolism research on the premise that hGH's lipid-related activity resides in this segment. This monograph covers what the C-terminal-fragment literature shows, how Fragment 176-191 relates to AOD-9604, and why human evidence for Fragment 176-191 itself is essentially absent. The AOD-9604 human trial record is covered in VialTalk's AOD-9604 monograph [20] and not repeated here.

Chemical identity and structure

The hGH C-terminal peptides studied since the 1970s are a family of overlapping synthetic sequences (172-191, 176-191, 177-191, 178-191 and shorter), not one molecule [1]. The best-characterised member, hGH 177-191, is reported as the 15-residue sequence Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe, with a disulfide bond between its two cysteines forming a cyclic peptide [10]. Two early papers print Arg-Val-Ser instead of Arg-Ser-Val mid-sequence [5][6].

Fragment 176-191 versus AOD-9604. AOD-9604 is described as hGH 177-191 with an added N-terminal tyrosine [13], whereas VialTalk's AOD-9604 monograph describes it as the 176–191 region with an added tyrosine [20]; Fragment 176-191 is the native hGH sequence one residue longer than 177-191. Naming in the literature is inconsistent: one 2026 review labels AOD9604 itself as "hGH 176-191" [14], while a 2026 anti-doping method lists "AOD9604" and "hGH 176-191" as separate analytes [18]. Vendor "Fragment 176-191" and AOD-9604 may be identical or near-identical; only the COA's stated sequence tells you which you have.

Mechanism of action

The working hypothesis is that hGH acts partly as a "pro-hormone" whose C-terminal region carries a distinct metabolic function [11]. The evidence is rodent and isolated-tissue work, mostly on 177-191 or AOD9604/AOD9401 rather than 176-191:

• Insulin/glucose effects (early work). In normal rats, 176-191 and related peptides containing the 178-191 core produced a short-lived rise in blood glucose and a more sustained rise in insulin, and reduced insulin sensitivity [1]. An insulin-antagonistic core was mapped to residues 178–190 [4]. In isolated islets, hGH 177-191 potentiated glucose-stimulated insulin release without stimulating release on its own [3]. Rat mechanism work followed [2].
• Lipid metabolism. hGH 177-191 showed antilipogenic activity in rat adipose tissue comparable to intact hGH, with no significant lipolytic effect in that assay [5], and it reduced glucose uptake in adipocytes from obese Zucker rats [6]. The later AOD9401 work reported stimulation of hormone-sensitive lipase and inhibition of acetyl-CoA carboxylase in rat adipose tissue [8].
• Receptor independence. AOD9604 did not compete for the hGH receptor and did not drive receptor-mediated cell proliferation in a transfected cell line [11]. Its lipolytic actions were not mediated directly through the β3-adrenergic receptor, although it increased β3-AR expression in obese mice [12].

Note the tension: early fragment studies reported hyperglycaemia and reduced insulin sensitivity [1][4], while later AOD-series studies reported no induced insulin resistance or hyperglycaemia [8][11]. Peptides, models and endpoints differ, so these cannot simply be merged.

What the research shows

Cell / in vitro. Islet and adipose studies are described above [3][5][6][8]. AOD-9401 increased lipolysis and decreased lipogenesis in isolated adipose tissue from obese rodents and humans [9] — an ex vivo result, not a human study. One 2022 study found chitosan nanoparticles co-loaded with hGH fragment 176-191 and doxorubicin more anti-proliferative in MCF-7 breast-cancer cells than doxorubicin-loaded particles alone [16]; that is a drug-delivery finding, not evidence of standalone anticancer activity.

Animal. hGH 177-191 reduced cumulative body-weight gain and adipose mass and inhibited lipogenesis in ob/ob mice [7]. AOD9401/AOD9604 reduced body-weight gain in obese Zucker rats and ob/ob mice, with increased fat oxidation and markers of lipolysis [8][9][11][12]. In β3-AR knock-out mice the chronic weight effect was lost [12]. LAT8881, a synthetic hGH C-terminal fragment of unstated exact sequence, improved outcomes in a mouse influenza model [19].

Human. No controlled human study of Fragment 176-191 under that name was found in the indexed library or in PubMed. Human trial data exist for AOD-9604, and VialTalk's AOD-9604 monograph covers them: the obesity trials did not demonstrate the hoped-for weight-loss benefit [20]. The LAT8881 authors mention clinical trials in obesity and neuropathy but do not report them [19]. Otherwise, the human record for "Frag 176-191" is reviews of non-medical use and one adverse-event report:

• Two 2026 reviews include it among unregulated performance/physique peptides (one under the label "AOD9604 (hGH 176-191)"), stressing limited clinical evidence and uncertain or mislabelled product composition [14][15].
• A French case report describes necrotising soft-tissue infection, requiring surgical debridement, in a person who had been using, without medical supervision, an internet-purchased product labelled HGH frag 176-191 [17].

Evidence quality

Low for Fragment 176-191 as a distinct compound. The record is preclinical, largely from one Monash University lineage [5][6][7][8][9][11][12], and mostly concerns 177-191 or AOD-series analogues. The only human efficacy data belong to AOD-9604, and those trials were negative on their primary aim [20]. Any claim that Fragment 176-191 is an established fat-loss agent goes beyond the evidence.

Research context

Fragment 176-191 sits in VialTalk's GH/IGF class next to AOD-9604 [20]; the AOD analogue does not act through the GH receptor [11]. AOD9604 is banned by the World Anti-Doping Agency [13], and hGH 176-191 is included in a 2026 doping-control screening method [18].

Storage and handling

Supplied as a lyophilized powder. Keep sealed vials refrigerated or frozen, dry and protected from light, and avoid repeated temperature cycling. No preparation guidance is given here.

Quality and COA considerations

• The COA should report the full sequence, including whether an N-terminal tyrosine is present, plus mass-spectrometry identity, HPLC purity and the intramolecular disulfide where applicable [10][13].
• Brand names such as "Frag 176-191", "AOD-9604" or "hGH fragment" are not interchangeable identity statements [14][18].
• Reviews flag uncertain composition, mislabelling and contamination in this supply chain [14][15], and the case report above involved an unregulated internet product [17]. A batch-specific COA and, for any sterile-use research work, sterility/endotoxin data are the minimum bar.

Key references

[1] Ng & Bornstein, Am J Physiol 1978 — https://pubmed.ncbi.nlm.nih.gov/645904/
[2] Ma et al., Biochim Biophys Acta 1982 — https://pubmed.ncbi.nlm.nih.gov/6810951/
[3] Weerasinghe & Bornstein, Am J Physiol 1978 — https://pubmed.ncbi.nlm.nih.gov/206156/
[4] Wade et al., Acta Endocrinol 1982 — https://pubmed.ncbi.nlm.nih.gov/6751009/
[5] Wu & Ng, Biochem Mol Biol Int 1993 — https://pubmed.ncbi.nlm.nih.gov/8358331/
[6] Wijaya & Ng, Biochem Mol Biol Int 1993 — https://pubmed.ncbi.nlm.nih.gov/8118430/
[7] Natera et al., Biochem Mol Biol Int 1994 — https://pubmed.ncbi.nlm.nih.gov/7987248/
[8] Ng et al., J Mol Endocrinol 2000 — https://pubmed.ncbi.nlm.nih.gov/11116208/
[9] Heffernan et al., Am J Physiol Endocrinol Metab 2000 — https://pubmed.ncbi.nlm.nih.gov/10950816/
[10] Ogru et al., J Pept Res 2000 — https://pubmed.ncbi.nlm.nih.gov/11152298/
[11] Heffernan et al., Int J Obes 2001 — https://pubmed.ncbi.nlm.nih.gov/11673763/
[12] Heffernan et al., Endocrinology 2001 — https://pubmed.ncbi.nlm.nih.gov/11713213/
[13] Cox et al., Drug Test Anal 2014 — https://pubmed.ncbi.nlm.nih.gov/25208511/
[14] Dominikowski et al., Front Endocrinol 2026 — https://pubmed.ncbi.nlm.nih.gov/42395176/
[15] Coutinho et al., J Sports Med Phys Fitness 2026 — https://pubmed.ncbi.nlm.nih.gov/41880199/
[16] Habibullah et al., Drug Des Devel Ther 2022 — https://pubmed.ncbi.nlm.nih.gov/35783198/
[17] Case report (French) — https://www.semanticscholar.org/paper/398a7019e946d3d57f588a9913c82e29519441d9
[18] Mazzarino et al., Analyst 2026 — https://pubmed.ncbi.nlm.nih.gov/42328738/
[19] Harpur et al., Clin Transl Immunology 2023 — https://pubmed.ncbi.nlm.nih.gov/36969366/
[20] VialTalk — https://vialtalk.com/forum/peptide-research-library/aod-9604-research-monograph-hgh-fragment-obesity-trials

Research-use note: Educational summary of published research on the hGH C-terminal fragment. The evidence is preclinical (rodent and isolated-tissue) and largely concerns 177-191 or AOD-series analogues. There are no controlled human studies of Fragment 176-191 under that name, and the related compound AOD-9604 did not show meaningful efficacy in its human obesity trials. Fragment 176-191 is not approved for human use in any major jurisdiction known to VialTalk. Nothing here is medical advice or a usage recommendation.