HGH Fragment 176-191

Overview

HGH Fragment 176-191 is a 16-amino-acid peptide corresponding to residues 176–191 of the C-terminus of human growth hormone. It emerged from work in the 1990s by Frank Ng, Michael Waters, and colleagues who mapped the lipolytic activity of hGH to its carboxyl-terminal region. The fragment was shown to retain fat-metabolism effects of the parent molecule while lacking the growth-promoting, IGF-1-inducing, and insulin-antagonizing actions mediated by the full-length protein.

Research on this fragment was central to the development of AOD-9604, an analog with a tyrosine added to the N-terminus to improve chemical stability. The two compounds share the same core sequence and largely similar pharmacology, though AOD-9604 was advanced through formal clinical development while HGH Fragment 176-191 itself remained primarily a research compound.

The fragment is popular in peptide research communities interested in fat loss research, though the clinical evidence in humans is limited and the compound is not approved for clinical use.

Structure / Chemistry

• Parent: Human growth hormone (191 amino acids)
• Fragment sequence: Residues 176–191 of hGH
• Length: 16 amino acids
• Molecular formula: approximately C78H125N23O23S2
• Molecular weight: approximately 1817 g/mol
• Class: Linear synthetic peptide, typically unmodified

AOD-9604 differs from HGH Fragment 176-191 by the addition of an N-terminal tyrosine residue, improving oxidative stability and manufacturing handling. The core biology is attributed to the shared downstream sequence, which lies outside the GH receptor-binding region of the parent molecule.

Mechanism of Action

The lipolytic actions of HGH Fragment 176-191 are proposed to occur through GH-receptor-independent mechanisms:

• Activation of hormone-sensitive lipase in adipocytes, mobilizing stored triglycerides
• Inhibition of lipogenic enzymes including acetyl-CoA carboxylase
• Stimulation of beta-3 adrenergic-like signaling pathways, though direct beta-3 agonism is not established
• Preservation of lean mass through apparent lack of antagonism of insulin signaling

Unlike full-length GH, HGH Fragment 176-191 does not activate hepatic IGF-1 production or produce hyperglycemia at typical research concentrations, which is the basis of its positioning as a "selective lipolytic" research peptide.

Research Summary

Clinical studies of HGH Fragment 176-191 itself are limited; most human data come from its AOD-9604 analog.

Pharmacokinetics

Research-grade HGH Fragment 176-191 is administered subcutaneously. Plasma half-life is short (estimated under an hour) due to rapid proteolysis and renal clearance. AOD-9604's N-terminal tyrosine modestly improves chemical stability but both compounds behave as short-duration peptides in vivo.

Distribution is broad, with uptake into adipose tissue contributing to the pharmacodynamic effect. Clearance is via peptide-typical proteolytic fragmentation and renal elimination of free amino acids and small fragments.

Common Discussion Topics

• Relationship between HGH Fragment 176-191 and AOD-9604
• Evidence level in humans vs rodents
• Claims of selective lipolysis without GH-typical side effects
• Research-grade purity and authenticity variability
• Positioning relative to full-length somatropin

Related Compounds

• AOD-9604 — N-terminal-tyrosine-stabilized analog
• Somatropin — full-length parent growth hormone
• IGF-1 LR3 — downstream GH axis effector
• CJC-1295 — upstream GHRH analog
• Ipamorelin — GH secretagogue on ghrelin pathway

Educational information only. HGH Fragment 176-191 is a research peptide not approved for clinical use. This article does not constitute medical, performance, or dosing advice.