HGH Fragment 176-191 — Research Overview
Chemical Name: Human growth hormone C-terminal fragment, amino acids 176 to 191 Also Known As: HGH Frag 176-191, GH Fragment 176-191, hGH 176-191, the lipolytic fragment Peptide Sequence: Tyr-Leu-Ala-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe Molecular Formula: C78H125N23O23S2 Molecular Weight: 1817.12 daltons Structure: 16-amino acid synthetic peptide corresponding to the native C-terminal sequence of human growth hormone, residues 176 through 191 Relationship to AOD-9604: HGH Fragment 176-191 is the direct native C-terminal sequence of human growth hormone. AOD-9604 is a closely related analog derived from this sequence, distinguished by the addition of a tyrosine residue at the N-terminus to improve stability and potency. The two share the same core lipolytic mechanism but are structurally distinct compounds. Published research exists specifically for HGH Fragment 176-191 as the native sequence, most notably the 1993 antilipogenic characterization study, as well as the broader body of research on its derivative AOD-9604. Category: Human growth hormone C-terminal fragment / selective lipolytic research peptide / fat metabolism research compound
Research Use Only — Disclaimer
The scientific literature on this page is provided strictly for educational and informational purposes. All Rogue Compounds products are intended for in-vitro laboratory research use only and are not approved by the FDA for human or animal consumption. The studies referenced below are independent third-party peer-reviewed publications. Rogue Compounds makes no claims that any product diagnoses, treats, cures, or prevents any disease or condition. Researchers are responsible for compliance with all applicable local, state, and federal regulations.
What Is HGH Fragment 176-191?
HGH Fragment 176-191 is a synthetic peptide corresponding precisely to the native C-terminal sequence of the 191-amino acid human growth hormone molecule, spanning residues 176 through 191. It represents the structural domain of human growth hormone that research has identified as responsible for the molecule’s lipolytic and anti-lipogenic metabolic effects, operating through pathways that are mechanistically independent of the growth-promoting, IGF-1-stimulating, and insulin-antagonizing effects that reside in other regions of the full hGH molecule.
Research into the structural basis of human growth hormone’s diverse biological activities identified that the intact hGH molecule functions, in effect, as a pro-hormone — different functional regions of the 191-amino acid chain mediate distinct biological effects. The N-terminal region of hGH is primarily responsible for its anabolic, growth-promoting, and insulin-antagonizing properties, acting through binding to the classical growth hormone receptor. The C-terminal domain — particularly the sequence spanning roughly residues 176 to 191 — was identified through systematic fragment studies as containing the structural elements responsible for the molecule’s fat metabolism activity, specifically its ability to promote lipolysis (fat breakdown) and inhibit lipogenesis (new fat synthesis).
By synthesizing just this C-terminal sequence, researchers created a tool for studying adipose tissue metabolism, lipolysis pathways, and energy balance in isolation from the broader endocrine effects of full hGH — without the growth promotion, IGF-1 elevation, insulin resistance, bone and organ enlargement risk, and glucose dysregulation associated with full growth hormone administration.
A critical honesty note for researchers: no human clinical trials have been published specifically for the unmodified HGH Fragment 176-191 sequence. The clinical trial data in this class — including Phase 2a and Phase 2b obesity trials — was conducted using AOD-9604, the N-terminally tyrosine-modified derivative. While the two compounds share the same mechanistic basis and target pathways, it is accurate to state that direct human pharmacokinetic, efficacy, and safety data for the unmodified 176-191 sequence as a standalone compound does not exist in the published clinical literature.
How HGH Fragment 176-191 Differs from Full hGH
This comparison is central to why HGH Fragment 176-191 is studied as a distinct research compound rather than as a proxy for full growth hormone.
Full human growth hormone (191 amino acids) binds the growth hormone receptor, stimulates IGF-1 production, promotes growth of bone and soft tissue, increases lean muscle mass, stimulates protein synthesis, antagonizes insulin action, raises blood glucose, and promotes lipolysis. These effects are not separable when using full hGH — they occur as a package.
HGH Fragment 176-191 (16 amino acids, residues 176-191) does not bind the classical growth hormone receptor. It does not stimulate IGF-1. It does not promote bone growth, organ growth, or soft tissue growth. It does not cause insulin resistance or raise blood glucose. It does not promote lean muscle mass through anabolic pathways. It preserves the lipolytic and anti-lipogenic effects of hGH while removing all of the above. This makes it valuable as a research tool for studying fat metabolism specifically, in the absence of confounding systemic hormonal effects.
Mechanism of Action
Beta-3 adrenergic receptor (ADRB3) pathway: The primary documented mechanism of HGH Fragment 176-191’s lipolytic activity involves the beta-3 adrenergic receptor, the major lipolytic receptor in adipose tissue. Research has demonstrated that the fragment increases ADRB3 expression in obese animals, restoring beta-3-AR RNA levels to those seen in lean controls. This receptor upregulation increases adipose tissue sensitivity to lipolytic signaling. Crucially, genetically modified mice lacking ADRB3 do not respond to the lipolytic effects of HGH fragment 176-191 or full hGH, directly confirming the pathway requirement.
Intracellular signaling cascade: ADRB3 activation triggers adenylyl cyclase stimulation, raising intracellular cyclic AMP (cAMP). Elevated cAMP activates protein kinase A (PKA), which phosphorylates and activates hormone-sensitive lipase (HSL) — the key enzyme that hydrolyzes stored triglycerides in fat cells into free fatty acids and glycerol released for oxidation. This is measurable as increased plasma glycerol, a direct quantitative index of lipolysis.
Anti-lipogenic activity: HGH Fragment 176-191 inhibits lipogenesis — the synthesis of new fatty acids and triglycerides from dietary carbohydrates — through actions on acetyl-CoA carboxylase, the rate-limiting enzyme for de novo fat synthesis. The 1993 published study of the closely related hGH 177-191 sequence specifically characterized the antilipogenic activity of the C-terminal domain. This dual mechanism — promoting fat breakdown while simultaneously inhibiting new fat formation — distinguishes the fragment’s effects from simple lipolysis stimulation.
Obesity-selective effect: Preclinical research consistently found that the lipolytic effects of HGH Fragment 176-191 were observed in obese animals but not in lean animals with normal body weight. This suggests that secondary regulatory pathways governing energy homeostasis modulate or override ADRB3-mediated lipolysis when body fat levels are at or near normal — an observation that has implications for understanding energy homeostasis regulation and opens questions for further research.
No GH receptor interaction: HGH Fragment 176-191 does not compete with full hGH for growth hormone receptor binding and does not induce cell proliferation, directly confirming that its activity does not operate through the classical GH receptor pathway.
Glycogen metabolism: Research in rodent muscle tissue has also identified potential effects of the C-terminal hGH fragment on glycogen synthase phosphatase inactivation, which may alter intracellular glycogen synthase activity and influence glucose metabolism at the muscle level. The implications of this effect require further investigation and have not been characterized in human subjects.
Published Research
Study 1 — Antilipogenic Activity of the C-Terminal Sequence hGH 177-191 (Foundational Characterization)
Authors: Wu ZH, Ng FM et al. Year: 1993 Journal: Biochemistry and Molecular Biology International PMID: 8358331 Full text: https://pubmed.ncbi.nlm.nih.gov/8358331/
This 1993 publication is the primary research directly characterizing the antilipogenic activity of the native C-terminal hGH sequence — the closest published literature specifically to the unmodified fragment rather than the AOD-9604 derivative. It examined the closely related hGH 177-191 sequence in rat adipose tissue.
The synthetic C-terminal peptide fragment of human growth hormone hGH 177-191 was shown to have antilipogenic activity identical with that of the intact molecule of human growth hormone.
No significant direct lipolytic effect of hGH 177-191 was found as determined by the rate of glycerol release from epididymal fat pads of peptide-treated rats under the specific assay conditions used.
The results support the hypothesis that the functional domain responsible for the antilipogenic activity of hGH resides in the C-terminal region of the molecule, and that a primary physiological effect of hGH in lipid metabolism operates at the level of lipogenesis rather than lipolysis alone.
This study established the antilipogenic characterization of the C-terminal domain and identified it as the structural basis for the fat metabolism activity of the full hGH molecule — providing the scientific foundation for all subsequent research on HGH Fragment 176-191 and its derivatives.
Study 2 — Hyperglycemic Effects of Synthetic C-Terminal Fragments: Mapping the Active Sequence
Authors: Ng FM, Bornstein J Year: 1978 Journal: American Journal of Physiology PMID: 645904 Full text: https://pubmed.ncbi.nlm.nih.gov/645904/
This early mapping study from the group that first identified the biologically active C-terminal sequences of hGH examined six different C-terminal fragments — residues 172-191, 176-191, 177-191, 178-191, 179-191, and 180-191 — for their in vivo biological effects in normal rats.
Four of the peptides (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 the other two (hGH 179-191 and 180-191) were inert in the systems tested.
A single dose of the peptides containing the 178-191 sequence significantly reduced insulin sensitivity in intravenous insulin tolerance tests.
These findings were important for establishing the minimum informational sequence required for biological activity in the C-terminal domain, and for identifying that hGH 176-191 specifically is among the active sequences — while also flagging early metabolic considerations that subsequent research and clinical work addressed through the AOD-9604 modification and longer-term tolerance data.
Study 3 — Oral Administration and Lipid Metabolism: Fragment Effects in Rodent and Human Adipose
Authors: Heffernan MA, Jiang WJ, Thorburn AW, Ng FM Year: 2000 Journal: American Journal of Physiology — Endocrinology and Metabolism Full text referenced via published literature on the C-terminal hGH fragment series
This study examined the effects of oral administration of synthetic C-terminal hGH fragment on lipid metabolism, using both rodent models and ex vivo human adipose tissue, providing cross-species mechanistic data.
The fragment stimulated lipolysis in isolated human adipocytes in vitro, confirming direct action on human fat cells and establishing the relevance of rodent mechanistic findings to human adipose tissue biology.
The fragment reduced lipogenesis and fat accumulation in obese animal models following chronic administration, with body weight gain reduced by approximately 50% in obese animals over a three-week treatment period compared to controls.
Effects on weight gain were observed in obese animals but not in lean controls with normal body weight — directly demonstrating the obesity-selective profile that has been consistently reproduced across the fragment research series.
IGF-1 levels were unaffected, blood glucose homeostasis was not disrupted, and insulin sensitivity was not altered — confirming clean metabolic separation from full hGH effects.
Study 4 — Beta-3 Adrenergic Receptor as Required Mediator: Knockout Confirmation
Authors: Heffernan M et al. Year: 2001 Journal: Endocrinology PMID: 11713213 Full text: https://pubmed.ncbi.nlm.nih.gov/11713213/
This mechanistic study used genetic knockout mouse models to establish that the beta-3 adrenergic receptor is not merely correlated with but mechanistically required for the lipolytic effects of the C-terminal hGH fragment.
The fragment increased beta-3-AR RNA expression in obese mice to levels comparable with lean controls, demonstrating restoration of adipose lipolytic receptor sensitivity suppressed in obesity.
In beta-3-AR knockout mice — animals genetically engineered to lack functional beta-3 adrenergic receptors — chronic treatment with the C-terminal hGH fragment produced no change in body weight and no increase in lipolysis, proving the pathway requirement definitively.
Fat oxidation as measured by indirect calorimetry increased in wild-type obese animals treated with the fragment, directly linking the receptor upregulation to increased energy expenditure through fat oxidation in vivo.
Study 5 — Selective Fat Metabolism: C-Terminal Fragment vs Full hGH in Obese Mice
Authors: Heffernan M et al. Year: 2001 Journal: Endocrinology PMID: 11673763 Full text: https://pubmed.ncbi.nlm.nih.gov/11673763/
This study directly compared the metabolic effects of the C-terminal hGH fragment with intact full-length human growth hormone side by side in obese mouse models, establishing the mechanistic profile that defines the fragment as a distinct research tool.
Both intact hGH and the C-terminal fragment significantly reduced body weight gain in obese mice, with associated increases in plasma glycerol levels confirming active lipolysis, and increased in vivo fat oxidation measured by indirect calorimetry.
Unlike intact hGH, the C-terminal fragment did not induce hyperglycemia or reduce insulin secretion — directly confirming the dissociation of lipolytic from diabetogenic activity within the hGH molecule.
The fragment does not compete for hGH receptor binding and does not induce cell proliferation — mechanistically establishing that fat metabolism activity of the C-terminal domain is independent of classical GH receptor signaling.
The authors concluded that fragments of hGH can act through mechanisms novel to traditional hGH-stimulated pathways, further establishing the concept that the 191-amino acid hGH molecule is a pro-hormone whose distinct biological activities are encoded in structurally separable domains.
Research Context and Honest Limitations
The published research base directly on HGH Fragment 176-191 as the unmodified native sequence is primarily preclinical — rodent models and isolated adipocyte studies. The 1993 antilipogenic characterization (PMID 8358331) is the most directly relevant primary publication for the specific 176-191 sequence.
The more extensive research program — including Phase 2a and Phase 2b human clinical trials — was conducted using AOD-9604, the N-terminally modified derivative that produced more consistent in vivo stability. Those clinical trials confirmed that the C-terminal hGH sequence class produces its lipolytic effects in humans without IGF-1 elevation, glucose disruption, or insulin sensitivity changes, and established GRAS safety status for the compound class. However, these trial findings derive from AOD-9604 specifically, not from the unmodified 176-191 sequence.
The Phase 2b obesity trial of AOD-9604 produced modest but real weight loss (approximately 1.8 kg greater than placebo over 12 weeks) and an excellent safety profile, but insufficient magnitude for regulatory obesity drug approval. Development for that indication was discontinued in 2007. Research interest subsequently expanded to cartilage repair and osteoarthritis applications based on emerging data from intra-articular models — a second research direction distinct from fat metabolism.
HGH Fragment 176-191 is classified as a prohibited substance by WADA.
Current Research Status
HGH Fragment 176-191 is not FDA-approved for any indication. No human clinical trials have been published using the unmodified 176-191 sequence specifically. It is studied as a research tool for investigating fat metabolism pathways, lipolysis mechanisms, beta-3 adrenergic receptor biology, and energy homeostasis — with secondary research interest in cartilage and connective tissue applications.
Reconstitution Note
HGH Fragment 176-191 is a water-soluble peptide. Bacteriostatic water is the standard reconstitution solvent. The fragment dissolves readily in bacteriostatic water without requiring acidic solvents. Always confirm the recommended solvent against the specific lot datasheet before reconstitution.
In-Use Period and Storage
Before Reconstitution — Lyophilized Powder
Rogue Compounds stores all products refrigerated prior to shipping to maintain compound integrity from production through to delivery. Upon receipt researchers should store vials at 2 to 8 degrees Celsius immediately. Keep vials sealed, dry, and away from direct light until ready for use. Do not freeze. Repeated freeze-thaw cycling has been documented in peer-reviewed pharmaceutical formulation literature to accelerate structural degradation even in dry powder form, potentially compromising molecular integrity and experimental reproducibility.
Why We Refrigerate Instead of Freeze
Freezing and thawing introduces mechanical and osmotic stress at the molecular level. Published pharmaceutical research identifies freeze-thaw cycling as a significant risk factor for loss of structural integrity in peptides and protein-based compounds. To protect compound quality at every stage of handling and fulfillment, Rogue Compounds maintains refrigerated rather than frozen cold chain storage throughout the entire process.
After Reconstitution — Liquid Solution
Store reconstituted solutions refrigerated at 2 to 8 degrees Celsius immediately after preparation. Protect from light at all stages of storage and handling. Avoid repeated freeze-thaw cycles of reconstituted solutions regardless of the diluent used. Use within the timeframe recommended for the individual compound. Label each aliquot with the compound name, concentration, date of reconstitution, and diluent used. Discard any solution that shows visible particulate matter, discoloration, or signs of contamination.
Note: Storage and in-use recommendations on this page are provided as general laboratory guidance based on standard peptide handling practices documented in peer-reviewed pharmaceutical literature. Researchers should always refer to the individual compound’s published research literature and datasheet for any specific requirements. All products sold by Rogue Compounds are intended strictly for in-vitro laboratory research use only.
Available from Rogue Compounds
View the HGH Fragment 176-191 product page: https://roguecompounds.com/hgh-frag-176-191/