What is HGH Fragment 176-191?
HGH Fragment 176-191 (also written HGH Frag 176-191, hGH 176-191 or somatotropin 176-191) names a 16-residue peptide matching the last 16 amino acids of human growth hormone (hGH), residues 176 to 191. PubChem records the native sequence as FLRIVQCRSVEGSCGF, closed by a disulfide bond between its two cysteines (CID 16131230). The name is not used consistently: some papers and catalogs apply it to the tyrosine-substituted sequence YLRIVQCRSVEGSCGF (Habibullah et al., 2022), which the anti-doping literature identifies as AOD-9604 (Cox et al., 2015).
Published work on this end of the hormone comes mainly from rat studies of synthetic C-terminal fragments in the late 1970s and early 1980s, adipose tissue work on the closely related 177-191 sequence in the 1990s, and recent analytical chemistry. Disguised Alpha supplies HGH Frag 176-191 as a lyophilized powder for laboratory research use only. Nothing on this page is guidance for use in people.
HGH Fragment 176-191 reference data
| Property | Value |
|---|---|
| Name | HGH Frag 176-191 |
| Aliases | HGH Fragment 176-191, hGH (176-191), somatotropin (176-191) (PubChem CID 16131230) |
| Sequence | Phe-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe (FLRIVQCRSVEGSCGF), with a 7 to 14 disulfide bond (PubChem CID 16131230) |
| Peptide class | C-terminal fragment of human growth hormone, residues 176 to 191 |
| Molecular formula | C₇₈H₁₂₃N₂₃O₂₂S₂ (PubChem CID 16131230) |
| Molecular weight | 1799.1 g/mol (PubChem CID 16131230) |
| CAS number | 66004-57-7 (PubChem CID 16131230) |
| Acetate salt record | C₈₀H₁₂₇N₂₃O₂₄S₂, 1859.1 g/mol (PubChem CID 172966176) |
| Tyrosine analog, for comparison | AOD-9604, YLRIVQCRSVEGSCGF, C₇₈H₁₂₃N₂₃O₂₃S₂, 1815.1 g/mol, CAS 221231-10-3 (PubChem CID 71300630) |
| Form | Lyophilized powder |
| Testing | Third-party tested, certificate published on the product page and in the COA portal |
The Compound Information panel on the product page does not print a sequence, formula, molecular weight or CAS number for this listing, so every identity value above comes from PubChem. One size is listed, and the certificate panel on the product page records the label mass and the measured content for the lot being shipped. Because the name covers two sequences that differ by one residue, confirm identity against your lot's certificate rather than from the name.
What the research covers
Published work relevant to HGH Fragment 176-191 falls into five areas. Each summary below states the model used and, where it matters, which sequence was tested.
Identity and naming
Three related sequences appear under similar names. Native hGH 176-191 begins with phenylalanine. The 15-residue hGH 177-191 sequence lacks that first residue; its cyclic form was called AOD in a structural study, and a 177-191 peptide was designated AOD9401 in rat work (Ogru et al., 2000; Ng et al., 2000).
AOD-9604 adds a tyrosine to the start of 177-191, so it is also 16 residues long and differs from native 176-191 only at position one (Cox et al., 2015). A 2026 review lists AOD9604 and hGH 176-191 as a single entry (Dominikowski et al., 2026), while a 2026 doping-control method reports them as two separate analytes (Mazzarino et al., 2026).
Glucose and insulin studies in rats
The earliest work compared synthetic C-terminal fragments of different lengths in normal rats. hGH 172-191, 176-191, 177-191 and 178-191 produced a short-lived rise in blood glucose and a more sustained rise in plasma insulin, while 179-191 and 180-191 were inactive, and the authors concluded that activity needed both the core sequence and the correct physical configuration (Ng and Bornstein, 1978).
In isolated rat islets, hGH 177-191 potentiated glucose-induced insulin release without stimulating release on its own (Weerasinghe and Bornstein, 1978). Chain-shortening experiments in normal rats, using reduced and S-carbamidomethylated peptides, placed the insulin-antagonistic core within residues 178 to 190 (Wade et al., 1982).
Adipose tissue models built on the 177-191 sequence
Work in the 1990s moved to fat metabolism. In rat adipose tissue, synthetic hGH 177-191 showed antilipogenic activity matching intact growth hormone, with no significant change in glycerol release (Wu and Ng, 1993). AOD9401 stimulated hormone-sensitive lipase and inhibited acetyl-CoA carboxylase in isolated rat adipose tissue and, over 20 days in obese Zucker rats, did not induce insulin resistance or glucose intolerance (Ng et al., 2000).
For the tyrosine analog, a mouse and cell study found that the peptide neither competed for the growth hormone receptor nor induced proliferation in receptor-transfected cells (Heffernan et al., 2001). These adipose results come from 177-191 or AOD-9604, not the native phenylalanine sequence, and they differ from the early rat studies in peptide form, duration and animal model, so the two sets of findings are not directly comparable.
Structure
Two-dimensional NMR of cyclic hGH 177-191 found type I beta-turns at Ser8-Val9-Glu10-Gly11 and Ser12-Cys13-Gly14-Phe15 of the peptide, and the authors reported partial structural similarity to the same region in the crystal structure of intact growth hormone (Ogru et al., 2000). The native 176-191 sequence carries the same two cysteines, recorded in PubChem as a ring between positions 7 and 14 (CID 16131230).
Cell culture, formulation and analytical work
A 2022 study loaded a peptide it called hGH fragment 176-191, specified as YLRIVQCRSVEGSCGF, into chitosan nanoparticles together with doxorubicin. Docking simulations predicted changes in doxorubicin binding to several breast cancer protein targets, and the dual-loaded particles showed greater antiproliferative activity against MCF-7 cells than particles carrying doxorubicin alone (Habibullah et al., 2022). That is one delivery study in one cell line, run with the tyrosine sequence.
Doping-control laboratories screen for hGH 176-191 as an analyte separate from AOD9604: a 2026 liquid chromatography and high-resolution mass spectrometry method for 54 prohibited compounds found hGH 176-191 extensively degraded after one week in serum and plasma at 4 and 22 degrees Celsius, stable for at least two months at -20 degrees Celsius, and detectable throughout the study in dried blood matrices (Mazzarino et al., 2026).
Key studies
- Ng FM, Bornstein J. "Hyperglycemic action of synthetic C-terminal fragments of human growth hormone." Am J Physiol. 1978. PMID 645904. DOI 10.1152/ajpendo.1978.234.5.E521. Normal rats: blood glucose, plasma insulin and insulin tolerance across six fragment lengths, including 176-191.
- Weerasinghe C, Bornstein J. "Effect of synthetic C-terminal fragments of hGH on insulin release by isolated islets." Am J Physiol. 1978. PMID 206156. DOI 10.1152/ajpendo.1978.234.5.E527. Isolated rat islets: glucose-induced insulin release and cAMP.
- Wade JD, et al. "Effect of C-terminal chain shortening on the insulin-antagonistic activity of human growth hormone 177--191." Acta Endocrinol (Copenh). 1982. PMID 6751009. DOI 10.1530/acta.0.1010010. Normal rats: chain-shortened, reduced peptides.
- Wu Z, Ng FM. "Antilipogenic action of synthetic C-terminal sequence 177-191 of human growth hormone." Biochem Mol Biol Int. 1993. PMID 8358331. Rat adipose tissue: lipogenesis and glycerol release.
- Ng FM, et al. "Molecular and cellular actions of a structural domain of human growth hormone (AOD9401) on lipid metabolism in Zucker fatty rats." J Mol Endocrinol. 2000. PMID 11116208. DOI 10.1677/jme.0.0250287. Isolated rat adipose tissue and a 20-day Zucker rat study.
- Ogru E, et al. J Pept Res. 2000. PMID 11152298. DOI 10.1034/j.1399-3011.2000.00771.x. Structural chemistry: two-dimensional NMR of cyclic hGH 177-191.
- Heffernan MA, et al. Int J Obes Relat Metab Disord. 2001. PMID 11673763. DOI 10.1038/sj.ijo.0801740. Obese and lean mice over 14 days, plus growth hormone receptor binding in transfected cells.
- Habibullah MM, et al. Drug Des Devel Ther. 2022. PMID 35783198. DOI 10.2147/DDDT.S367586. Molecular docking and MCF-7 cell culture with chitosan nanoparticles, tyrosine sequence.
- Mazzarino M, et al. "Rapid and harmonized analytical workflow for the determination of peptidic and non-peptidic doping agents in dried and liquid blood matrices." Analyst. 2026. PMID 42328738. DOI 10.1039/d6an00455e. Analytical chemistry: detection and storage stability in serum, plasma and dried blood.
Handling and storage of lyophilized HGH Frag 176-191
General laboratory practice for this material:
- Store the lyophilized powder at -20°C, protected from light, until use (storage guidance on the product page).
- Let the sealed vial reach room temperature before opening so moisture does not condense on the powder.
- The peptide carries a disulfide bond between Cys7 and Cys14 (PubChem CID 16131230), and early structure-activity work found that configuration affected activity (Ng and Bornstein, 1978), so keep reducing agents such as dithiothreitol and 2-mercaptoethanol out of stock solutions unless the experiment calls for them.
- In a 2026 method study, hGH 176-191 degraded within a week in serum and plasma at 4 and 22 degrees Celsius but held for at least two months frozen (Mazzarino et al., 2026), so keep liquid holding times short.
- After reconstitution, keep solutions at 2 to 8°C and protected from light, and split stock into single-use aliquots to avoid freeze/thaw cycles.
- Record the lot number and keep its certificate with your notes. For quantitative work, use the measured content and molecular weight on the certificate rather than the label mass.
Frequently asked questions
What is HGH Fragment 176-191?
A synthetic 16-residue peptide matching residues 176 to 191 of human growth hormone, FLRIVQCRSVEGSCGF, cyclized by a disulfide bond (PubChem CID 16131230). Its main published record is early rat work on glucose and insulin (Ng and Bornstein, 1978) and recent analytical chemistry.
Is HGH Frag 176-191 the same as AOD-9604?
Not by definition. Native hGH 176-191 starts with phenylalanine (1799.1 g/mol, CID 16131230), while AOD-9604 starts with tyrosine (1815.1 g/mol, CID 71300630), a difference of one oxygen atom. The names are still used interchangeably in some papers and catalogs (Habibullah et al., 2022; Dominikowski et al., 2026), so the measured mass on the certificate settles which one a lot contains. See our AOD-9604 listing and its research guide.
Is HGH Frag 176-191 a peptide or a hormone?
It is a peptide: 16 amino acids taken from the 191-residue growth hormone protein. For the closely related tyrosine analog, receptor assays in transfected cells found no competition for the growth hormone receptor (Heffernan et al., 2001). We did not find comparable receptor data for the native sequence in PubMed.
Why do sources list different molecular weights?
They describe different species. The native cyclic peptide is 1799.1 g/mol (CID 16131230), the acetate salt record is 1859.1 g/mol (CID 172966176), and the tyrosine analog is 1815.1 g/mol (CID 71300630). Some listings print CAS 221231-10-3 and about 1815 g/mol under the 176-191 name; those values belong to AOD-9604. For quantitative work, use the formula and measured content on your lot's certificate.
How should HGH Frag 176-191 powder be stored?
Keep the lyophilized powder at -20°C and protected from light. After reconstitution, store the solution at 2 to 8°C, protected from light, and avoid freeze/thaw cycles, as listed on the product page.
Where can researchers buy HGH Frag 176-191?
Disguised Alpha sells it for laboratory research, third-party tested with the certificate published on the product page: HGH Frag 176-191.
Related compounds and guides
- AOD-9604 and its research guide: the tyrosine analog of this fragment
- Tesamorelin and its research guide: a GHRH analog rather than a growth hormone fragment
- Sermorelin Acetate and CJC-1295 No DAC
- Ipamorelin and its research guide: a growth hormone secretagogue studied through a different receptor
- IGF1-LR3 and its research guide
- COA portal: every published certificate, by lot
This product is for research use only. It has not been evaluated for safety or effectiveness in humans. Not for human consumption. All products are intended for laboratory research purposes only.