hGH Fragment 176-191

Overview

hGH Fragment 176-191 is the C-terminal 16-amino-acid segment of mature human growth hormone. The identity protected on this page is the native F-start peptide FLRIVQCRSVEGSCGF, not the modified Y-start analog AOD-9604.

The distinction matters because commercial pages, papers and product labels sometimes use “hGH 176-191” for the Y-start molecule. Results cannot be transferred between the two identities merely because the names are used interchangeably.

Verified identity

PubChem records native somatotropin (176-191) as CID 16131230, CAS 66004-57-7, formula C78H123N23O22S2 and computed molecular weight 1799.1 g/mol. Its IUPAC record and the terminal sequence of UniProt human growth hormone support the 16-residue sequence:

FLRIVQCRSVEGSCGF

The two cysteines form a disulfide bond between positions 7 and 14. This structural loop is part of the identity; a loose name without sequence or analytical confirmation is not enough to establish which substance was tested.

Not the same molecule as AOD-9604

FDA defines AOD-9604 as hGH residues 177-191 with an additional N-terminal tyrosine. Equivalently, it is the F176Y analog of hGH 176-191. The anti-doping literature uses the same Y-start definition. AOD-9604 is therefore a close analog, but not a synonym for native hGH 176-191.

Direct biological evidence

The clearest primary study located for the native fragment was published in 1978. Researchers administered synthetic hGH fragments, including 176-191, to normal rats. The fragments spanning 172-191 through 178-191 produced a short-lived rise in blood glucose and a more sustained rise in plasma insulin. A single animal dose of fragments containing the 178-191 sequence also reduced insulin sensitivity in intravenous insulin-tolerance testing.

This result does not demonstrate fat loss, safety or clinical benefit in humans. It also cautions against carrying AOD-9604 marketing claims such as “no glucose effect” over to the native fragment.

Human evidence and registry search

No human clinical study of the unmodified native fragment was located in the bounded PubMed and ClinicalTrials.gov review completed on 21 August 2026. The combined ClinicalTrials.gov search did identify three completed later studies of the Y-start molecule under the code LAT8881; those are AOD-9604 studies and are not evidence for native hGH 176-191.

The search result is not proof that no human exposure has ever occurred. It means this review found no registered clinical program supporting a human indication, dose or benefit for the native fragment.

Mechanism claims and limits

The native fragment is often marketed as the “lipolytic part” of growth hormone. The source set reviewed here does not establish that claim as a human effect of the native F-start peptide. The historical rat study measured glucose, insulin and insulin sensitivity; it did not establish human weight loss.

Positive fat-metabolism studies commonly cited in this area concern AOD-9604, the Y-start analog, in rodents. Even AOD-9604 later failed to show significant weight loss versus placebo in its larger obesity program. Mechanistic similarity is therefore not a substitute for molecule-specific clinical evidence.

Safety boundaries

No human pharmacokinetic, pharmacodynamic or controlled safety dataset for native hGH Fragment 176-191 was identified. The animal glucose and insulin findings cannot be converted into a quantitative human risk estimate, but they prevent a “metabolically neutral” or “side-effect free” conclusion.

Peptide products also carry identity, aggregation, impurity and immunogenicity uncertainties. These product-level risks are separate from the intrinsic biology of a correctly identified peptide.

Russian-language evidence and product identity

The Russian-language sources reviewed did not add verified human evidence for native hGH 176-191. A 2014 analytical study tested three internet products sold as “HGH 176-191.” It reported a Y-start sequence, YLRIVQCRSVEGSCGF, and a mass around 1815.9 Da—an AOD-9604-like identity rather than the native F-start peptide—and found impurity compounds in all three samples.

Small Russian rat abstracts likewise used commercial material labelled “HGH(176-191).” Without independent analytical verification, those results cannot be assigned to native hGH 176-191. This is evidence of nomenclature and product-quality confusion, not independent human efficacy evidence.

Regulatory and sport status

This page does not provide a country-by-country legal conclusion. Regulatory status depends on the product, intended use and jurisdiction; lack of a specifically named ban would not make a product approved or lawful for human use.

For sport, the distinction is explicit: the 2026 WADA Prohibited List names AOD-9604 and hGH 176-191 separately as growth-hormone fragments under S2.2.3. They are prohibited at all times for athletes subject to the World Anti-Doping Code.

What the evidence supports

• Verified: native hGH 176-191 is the F-start 16-mer FLRIVQCRSVEGSCGF.
• Verified: AOD-9604 is the distinct Y-start analog YLRIVQCRSVEGSCGF.
• Preclinical only: located native-fragment studies are animal or laboratory work; the rat experiment reported glucose, insulin and insulin-sensitivity effects.
• Not established: human fat loss, a human mechanism, pharmacokinetics, safety, dose or treatment benefit.
• Product-quality signal: some products and papers labelled “hGH 176-191” actually describe an AOD-like Y-start peptide and may contain impurities.
• Sport: both separately named molecules are prohibited under WADA S2.2.3 in 2026.