HGH Fragment 176-191: Research Overview

HGH Fragment 176-191 is a 16-amino-acid peptide corresponding to residues 176 through 191 at the C-terminus of human growth hormone (hGH). It was developed by researchers at Monash University and initially investigated under the designation AOD9604 as a potential obesity drug candidate. The peptide’s appeal in preclinical research stemmed from evidence that it could reproduce the lipolytic (fat-mobilizing) actions of full-length hGH without activating the GH receptor — a property that theoretically sidesteps the insulin resistance, edema, and carpal tunnel effects associated with supraphysiological GH levels. However, the compound failed to demonstrate efficacy in human obesity trials, and no published human dose-ranging study exists for the fragment in its subcutaneous form as sold by research-chemical vendors.

What is HGH Fragment 176-191?

HGH Fragment 176-191 (also labeled as hGH Frag 176-191, AOD9401, or simply Frag 176-191) is a 16-residue peptide with a molecular weight of approximately 1817 Da. It spans the C-terminal helical domain of human GH that is implicated in regulating fat metabolism, and it is often described as a “lipolytic fragment.” Research-chemical vendors sell it as a lyophilized powder in 2 mg, 5 mg, or 10 mg vials under various label names; the underlying sequence is identical across these formulations when verified by certificate of analysis (COA). The compound is not approved by the FDA, EMA, TGA, or any other major drug regulatory authority for human therapeutic use.

Mechanism of Action

The C-terminal region of hGH (residues 176–191) is structurally distinct from the receptor-binding domains of the full-length protein. Unlike full-length GH, which binds the GH receptor (GHR) and activates the JAK2/STAT5 axis to promote anabolism and IGF-1 production, HGH Fragment 176-191 does not bind GHR at pharmacologically relevant concentrations. Instead, it is proposed to interact with adipocyte surface receptors linked to adenylate cyclase, increasing intracellular cAMP and activating the lipolytic enzyme cascade (protein kinase A → hormone-sensitive lipase → adipose triglyceride lipase).

Preclinical work also showed that HGH Fragment 176-191 downregulates lipogenic enzymes such as acetyl-CoA carboxylase (ACC), suggesting a dual mechanism: accelerated lipolysis plus reduced lipid synthesis. Critically, while the lipolytic effects of full-length hGH partly depend on β3-adrenergic receptor (AR) signaling, Heffernan et al. (2001, PMID 11713213) demonstrated that the lipolytic actions of both hGH and AOD9604 persist in β3-AR knockout mice — indicating that the fragment’s mechanism operates largely independently of the β3-AR pathway.

What the Research Shows

The strongest preclinical evidence comes from Heffernan et al. (2001, PMID 11673763), which demonstrated that chronic treatment with HGH Fragment 176-191 significantly reduced adipose accumulation and increased fat oxidation in obese mice, matching the effect of full-length hGH while avoiding the growth-promoting and insulin-desensitizing properties of the full molecule. A follow-up paper (Heffernan et al., Endocrinology 2001, PMID 11713213) confirmed that the lipolytic mechanism is β3-AR-independent.

Early human metabolic research using an oral formulation of the synthetic fragment was reported by Ng et al. (J Endocrinol, 2000; PMID 10950816), who observed dose-dependent alterations in lipid metabolism. However, subsequent randomized controlled trials of the oral AOD9604 formulation in adults with obesity failed to achieve the co-primary weight-loss endpoint required for FDA approval, and the obesity drug development program was discontinued. No published human dose-ranging study exists for subcutaneously administered HGH Fragment 176-191 using the lyophilized form sold by research vendors. The human evidence base is therefore limited to early-phase oral-formulation research and preclinical studies.

Pharmacokinetics

Human pharmacokinetic data for subcutaneously administered HGH Fragment 176-191 are not available in the published literature. Preclinical data in rodents indicate a short plasma half-life (approximately 30 minutes or less) following intravenous or subcutaneous administration, consistent with rapid proteolytic clearance of a small peptide without any half-life-extending modifications. Peak plasma concentrations after SC injection in rodent models are reached within 15–30 minutes. The absence of GH receptor binding means there is no prolonged receptor-mediated effect analogous to what is seen with GH or GHRH analogs.

Common Research Dose Ranges

Not medical advice. These are ranges reported in research literature, not personalized recommendations. Consult your physician.

No published human dose-ranging study exists for subcutaneously administered HGH Fragment 176-191 in its lyophilized research-chemical form. The literature from preclinical murine lipolysis studies (Heffernan et al., 2001; PMID 11673763) and early-phase human lipid-metabolism research (Ng et al., 2000; PMID 10950816) reports dose ranges of approximately 250–1000 mcg, with daily subcutaneous administration evaluated in preclinical studies and oral formulations in the early human research. These figures derive from preclinical or oral-route data and cannot be directly translated to subcutaneous use in humans.

Storage

Lyophilized HGH Fragment 176-191 should be stored at −20 °C, protected from moisture and light. Once reconstituted with bacteriostatic water, the solution should be kept at 2–8 °C and used within 28 days. As with other small peptides, repeated freeze-thaw cycles are inadvisable.

What HGH Fragment 176-191 Is NOT

HGH Fragment 176-191 is not full-length human growth hormone. It does not bind the GH receptor, does not elevate IGF-1, and does not produce the anabolic, growth-promoting, or insulin-desensitizing effects of exogenous rhGH. It is also distinct from AOD-9604, which refers to a slightly modified version of the fragment (sometimes with a Tyr at the N-terminus or different acetylation) used in the Monash drug development program; the two share overlapping sequence but are not identical across all vendor preparations. Additionally, HGH Fragment 176-191 is not the same compound as ipamorelin, sermorelin, or CJC-1295 — none of those peptides derive from the GH sequence, and all operate through completely different receptor pathways.

References

Citations for this guide are listed below. All PubMed links resolve to the NCBI abstract page for the referenced article.