Fragment 176-191

Fragment 176-191 is the C-terminal amino acid sequence spanning residues 176 through 191 of human growth hormone (hGH). This region of the hGH molecule was identified in early research as containing the domain responsible for the hormone's lipolytic activity, functionally separable from the N-terminal domain that binds the classical GH receptor and drives IGF-1 secretion.

Because Fragment 176-191 does not bind the classical GH receptor, it does not stimulate IGF-1 production, promote long-bone growth, or impair glucose metabolism — effects characteristic of exogenous full-length hGH. Its metabolic actions are therefore proposed to be more targeted than those of the parent hormone.

At the cellular level, studies in adipocyte preparations and rodent models attribute the fragment's lipolytic activity to two complementary enzymatic effects: • Stimulation of hormone-sensitive lipase (HSL), the primary enzyme responsible for hydrolysis of stored triglycerides in adipose tissue. • Inhibition of acetyl-CoA carboxylase (ACC), a rate-limiting enzyme in de novo lipogenesis, thereby suppressing new fat synthesis alongside promoting breakdown.

Research using beta-3 adrenergic receptor (beta-3 AR) knockout mice demonstrated that AOD9604 — a structurally analogous compound derived from the same region (see clinical section) — loses its chronic fat-reducing effect in the absence of functional beta-3 AR. Both peptides also upregulate beta-3 AR expression in obese animals toward levels seen in lean controls, suggesting a feedback amplification of lipolytic signaling. Diacylglycerol has been proposed as an intracellular second messenger in the downstream signaling cascade. The precise receptor that Fragment 176-191 engages upstream of these effects remains incompletely characterized.

A critical distinction must be established at the outset. Fragment 176-191, the native hGH sequence (CAS 66004-57-7), has not been studied in humans. The human clinical data commonly cited in reference to this peptide was generated using AOD9604, a structurally modified analog in which the phenylalanine at the N-terminus is replaced by tyrosine, rendering it a 16-amino acid peptide (residues 177-191 with a modified terminus) with greater plasma stability. The two compounds are frequently conflated in popular sources.

The foundational animal study by Heffernan and colleagues (Endocrinology, December 2001; PMID 11713213; DOI 10.1210/endo.142.12.8522) established that both full-length hGH and AOD9604 reduced body weight and adipose tissue mass in genetically obese (ob/ob) mice after 14 days of chronic intraperitoneal administration. In beta-3 AR knockout mice, chronic weight-reducing effects were abolished, though acute energy expenditure effects persisted, indicating involvement of both beta-3 AR-dependent and independent pathways.

Human clinical development of AOD9604 was conducted by Metabolic Pharmaceuticals Ltd. (Melbourne, Australia) across six randomized, double-blind, placebo-controlled trials collectively enrolling approximately 900 subjects. A 12-week Phase IIa trial in 300 obese adults testing six oral doses (0, 1, 5, 10, 20, and 30 mg/day) showed the 1 mg/day group lost a mean of 2.8 kg versus 0.8 kg in placebo, with accompanying modest improvements in cholesterol profiles. However, a subsequent 24-week Phase IIb trial (the OPTIONS study; n=536, 16 sites in Australia; oral doses of 0.25, 0.5, and 1 mg/day) failed to demonstrate statistically significant weight loss compared to placebo. Metabolic Pharmaceuticals discontinued development in 2007 on the basis of this result.

Safety data from across all six trials were summarized by Stier, Vos, and Kenley in the Journal of Endocrinology and Metabolism (2013; DOI 10.4021/jem157w). The overall tolerability profile was described as "indistinguishable from placebo." No elevation in IGF-1, no impairment of glucose tolerance, and no anti-AOD9604 antibodies were detected in any of the approximately 700 subjects treated with active drug. There is no comparable human clinical dataset for Fragment 176-191 itself.

A separate 2022 in vitro study (Habibullah et al.; PMID 35783198) explored Fragment 176-191 in combination with doxorubicin-loaded chitosan nanoparticles against MCF-7 breast cancer cells, reporting enhanced anti-proliferative activity. This study is exploratory and does not address the metabolic properties of the peptide.

Typical dosage: 250-500 mcg (daily).

No FDA-approved or officially recommended dosing protocol exists for Fragment 176-191 or AOD9604 for any indication. All dosing information below reflects research protocols or compounding/community practice and should not be used as a basis for self-administration.

In the human clinical trials of AOD9604, the oral route was employed at doses ranging from 0.25 to 30 mg once daily. The 1 mg/day oral dose produced the most favorable weight-loss signal in the Phase IIa trial; higher oral doses did not show superior efficacy and were associated with more gastrointestinal adverse events at 54 mg. Intravenous doses in earlier single-dose human pharmacokinetic studies ranged from 25 to 400 mcg/kg body weight.

In compounding and wellness clinic settings — where Fragment 176-191 is dispensed as a research peptide — subcutaneous injection is the dominant route. Community protocols typically describe: • 250 to 500 mcg administered subcutaneously once daily. • Injection commonly timed to the morning in a fasted state, on the premise that lipolytic signaling may be enhanced in the absence of elevated insulin. • Cycle lengths of 8 to 12 weeks are commonly reported, followed by a rest period.

These subcutaneous protocols are derived from extrapolation of animal data and clinical trial doses and have not been validated in controlled human studies for Fragment 176-191 or AOD9604.

This information is provided for educational reference only and does not constitute medical advice. Anyone considering use of this or any peptide compound should consult a qualified physician.

No compound-specific stability data has been identified for this peptide. The general lyophilized-peptide handling framework applies — see Storage & handling for temperature, reconstitution diluent, and beyond-use dating principles.

No controlled clinical trials have evaluated Fragment 176-191 in combination with any other peptide or drug. All combination strategies described below originate from community practice, wellness clinics, and speculative pharmacological reasoning; they are anecdotal.

The most frequently cited combination pairs Fragment 176-191 with CJC-1295 (a growth hormone-releasing hormone analog) and ipamorelin (a selective GH secretagogue). The stated rationale is pharmacological complementarity: CJC-1295 and ipamorelin are thought to amplify endogenous GH pulse amplitude and duration, while Fragment 176-191 is expected to contribute direct lipolytic activity without raising IGF-1. Proponents argue that endogenous GH stimulated by these secretagogues may synergize with the fragment's direct effects on adipocyte enzyme activity. This reasoning is mechanistically plausible but entirely unsupported by human trial data.

Fragment 176-191 is also anecdotally described in combination with sermorelin (another GHRH analog) for similar reasons. Some wellness protocols add the peptide to semaglutide or other GLP-1 receptor agonist regimens, with the unstated assumption that different mechanisms of reducing adiposity are additive; no evidence supports this in either direction.

The safety of these combinations in humans has not been evaluated in any published study.

Fragment 176-191 is not currently FDA-approved for any indication. It is generally classified as a research compound. Regulatory status varies by country.

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Reported side effects: Minimal reported side effects

The safety data available for this class of peptides derives from AOD9604, not from Fragment 176-191 directly. Fragment 176-191 has no published human safety or tolerability data.

From the AOD9604 human trials (Stier et al. 2013; approximately 900 subjects across six trials): • The overall adverse event profile was statistically indistinguishable from placebo across the study population. • Common adverse events were mild to moderate and included headache, fatigue, gastrointestinal symptoms (diarrhea, flatulence, nausea), dizziness, and injection-site reactions (redness, swelling, bruising). • Gastrointestinal adverse events increased at the highest oral dose tested (54 mg/day), suggesting a dose-dependent component. • In one Phase I study of intravenous dosing (15 healthy male subjects, 25-400 mcg/kg IV), 12 of 15 subjects reported a total of 29 adverse events; headache and fatigue were most common. • No IGF-1 elevation was detected at any dose, distinguishing it from full-length hGH administration. • No impairment of glucose tolerance or insulin sensitivity was observed. • No anti-AOD9604 antibodies were detected, indicating no immunogenicity. • No acceleration of long-bone growth, no organ hyperplasia, and no adverse cardiovascular signals were reported.

Injection-site reactions (erythema, induration, pruritus) are the most common adverse events reported in compounding/subcutaneous use. Rotating injection sites and using properly reconstituted bacteriostatic water are the standard mitigation measures cited in clinical protocols.

Contraindications and special populations have not been formally evaluated. Neither Fragment 176-191 nor AOD9604 is approved by the FDA for any use in humans. AOD9604 appears on the World Anti-Doping Agency (WADA) prohibited list and is therefore banned in competitive athletes. Individuals with active malignancy should exercise particular caution given the preliminary in vitro oncology research noted above and the absence of relevant human safety data in that context.