Fragment 176-191 Monograph — Research Compound Reference

"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

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.