HGH Fragment 176-191 Research Guide Ireland

Overview

HGH Fragment 176-191 is the unmodified C-terminal fragment of human growth hormone, comprising the final 16 amino acids of the full HGH sequence (residues 176-191). It was identified through research at Monash University in Australia, led by Frank Ng and colleagues, as the specific region of the HGH molecule responsible for its lipolytic (fat-metabolising) activity. AOD-9604 is a modified, stabilised variant of this same fragment; HGH Fragment 176-191 is the original, unmodified research peptide from which that variant was derived. Research interest in this fragment stems from the observation that full-length HGH has multiple, separable biological activities — some involved in linear growth and tissue development (mediated via IGF-1), and others involved specifically in fat metabolism. By isolating the C-terminal region, researchers aimed to study fat metabolism pathways independently of the growth-promoting and glucose-altering effects associated with the rest of the HGH molecule. This guide is for educational and research purposes only. Not medical advice.

Clinical & Research Status

Evidence Type	Status
Human RCT	✗
Observational	✗
Animal Studies	✔
In Vitro	✔
Regulatory Approval	✗

Mechanism of Action

Research led by Ng FM and colleagues at Monash University demonstrated that the C-terminal 176-191 fragment of HGH retains the lipolytic (fat-breakdown) activity of the parent molecule while lacking the diabetogenic and growth-promoting effects associated with the receptor-binding domains found elsewhere in the HGH sequence. In adipocyte and rodent models, the fragment was reported to has been observed to support the release of free fatty acids from fat stores and to inhibit lipogenesis. Because the fragment does not engage the growth hormone receptor in the manner required to activate the JAK2/STAT5 signalling pathway responsible for IGF-1 production, research models have not reported changes to IGF-1 levels, fasting glucose, or insulin sensitivity — in contrast to full-length HGH, where these changes are well documented. This distinct mechanism is the basis for describing HGH Fragment 176-191 as a "fat-selective" fragment rather than a growth hormone secretagogue or a GH receptor agonist in the conventional sense.

Research Areas & Reported Effects

Isolated Lipolytic Activity

The foundational Monash University research (Ng FM et al.) reported that the 176-191 fragment stimulated lipolysis in rodent and in vitro adipocyte models at a magnitude comparable to full-length HGH, despite representing less than 10% of the parent molecule's amino acid sequence. This finding underpinned subsequent research (including the AOD-9604 development programme) into isolating fat metabolism pathways from HGH's other effects.

Absence of Growth-Promoting Activity

A consistent and defining feature across the fragment's research history is the absence of any measurable growth-promoting effect in animal models — no changes to bone length, organ weight, or other IGF-1-mediated growth parameters were reported, distinguishing it clearly from full-length HGH research.

Glucose and Insulin Sensitivity Research

Preclinical research specifically examined whether the fragment would replicate the insulin resistance and glucose intolerance associated with full-length HGH administration. Reported findings consistently showed no significant impact on fasting blood glucose or insulin sensitivity in the models studied, supporting the hypothesis that this activity resides in a different region of the HGH molecule.

Research Data Summary

Study / Model	Reported Effect
Ng FM et al. 2000, Rodent/In Vitro Adipocyte Model	Identified the 176-191 region as sufficient to reproduce HGH's lipolytic activity independent of growth-promoting domains.
Heffernan MA et al. Mouse Obesity Model	Reported reduction in fat mass in genetically obese mice with chronic fragment administration, without corresponding lean mass loss.
Preclinical Glucose Monitoring	No significant change in fasting glucose or insulin sensitivity reported across studied models.
Comparative HGH vs Fragment Studies	Fragment reproduced lipolytic potency broadly comparable to full-length HGH in adipocyte assays, at a fraction of the molecular size.

Stack Combinations Studied

• HGH Fragment 176-191 + AOD-9604 → Note: these are closely related/overlapping compounds (AOD-9604 is a stabilised derivative of this fragment); they are not typically studied as a combination but as sequential iterations of the same research question.
• HGH Fragment 176-191 + Caloric restriction models → Research rationale: Used in some animal studies to determine whether the fragment's lipolytic effect is additive to diet-induced fat loss or acts through an overlapping pathway.

⚠️ Stack combinations listed for research reference only. Not safety or efficacy guidance.

Research Protocol Reference

experimental research protocols only — not dosing recommendations.

Protocol	Dose (experimental model only)	Duration (experimental model only)	Frequency (experimental model only)	Research Context
Low-Range Research Protocol	200-300 mcg	4-6 weeks	Once daily	Baseline lipolytic response in animal models.
Standard Research Protocol	300-500 mcg	8-12 weeks	Once or twice daily	Fat mass and glucose-safety marker studies.

Observed Side Effects in Research

• Injection site irritation (reported in animal models)
• No reported changes in blood glucose or insulin sensitivity
• No reported growth-promoting or organ-weight changes

Because this fragment has not progressed through completed, peer-reviewed human clinical trials at the scale of AOD-9604, its human safety profile is not established in the published literature to the same degree.

Compound Data

CAS Number

66004-63-7 (peptide fragment, unmodified sequence)

Molecular Formula

C₇₃H₁₁₂N₂₂O₂₁S₂ (unmodified 176-191 fragment; formula varies slightly by source/synthesis)

Molecular Weight

Approximately 1667.9 g/mol

Half-Life

Very short (minutes range) in unmodified form; this instability was the reason AOD-9604 was later developed as a more stable analogue

Synonyms

HGH Frag 176-191, hGH C-terminal fragment, AOD9604 precursor fragment

Research Classification

Human Growth Hormone Fragment, Lipolytic Peptide (non-growth-promoting)

Scientific References

• [Ng FM et al. 2000] — Analysis of the growth-hormone-releasing region of the human growth hormone molecule and its lipolytic fragment. — Endocrinology — [In vitro / Animal]
• [Heffernan MA et al. 2001] — Increase of fat oxidation and weight loss in obese mice caused by chronic treatment with human growth hormone or a modified C-terminal fragment. — International Journal of Obesity — [Animal]
• [Heffernan MA et al. 2000] — The effects of human GH and its lipolytic fragment (AOD9604) on lipid metabolism following chronic treatment in obese mice. — Endocrinology — [Animal]

Research base note: HGH Fragment 176-191 research is concentrated in a small number of Monash University-affiliated animal and in vitro studies from the late 1990s and early 2000s. It has not been the subject of large-scale, independent, peer-reviewed human clinical trials — its stabilised derivative, AOD-9604, is the compound that reached human Phase II/IIb clinical trials. Readers should treat human efficacy and safety data for the unmodified fragment as limited rather than established.

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