Full Name: Human Growth Hormone Fragment 176–191, abbreviated as HGH Frag 176-191
CAS Number: 66004-57-7 (Free base form; CAS numbers for acetylated/amidated variants differ slightly)
Molecular Formula (typical unmodified version): C₇₈H₁₂₃N₂₃O₂₃S
Molecular Weight: Approximately 1815–1817 Da (Very close to AOD9604, AOD9604 has an additional Tyr, hence slightly larger by a few Da)
Sequence: FKDLS (Phe-Lys-Asp-Leu-Ser), i.e., hGH The last six amino acids at the C-terminus; some manufacturers offer variants with N-terminal acetylation or C-terminal amidation to improve stability.
Appearance: White to off-white lyophilized powder
Purity: Research grade typically labeled ≥98% (HPLC)
Solubility: Soluble in dilute acetic acid/sterile water/antibacterial water; solubility in pure water is low, it is recommended to use water containing 0.1% acetic acid or BAC to aid dissolution.
Storage: Unreconstituted, -20℃, protected from light and moisture; reconstituted, refrigerate at 2-8℃, best used within 24-72 hours. Repeated freeze-thaw cycles will cause the hydrophobic short peptides to aggregate and become inactive.
HGH Frag extracts the six amino acids from positions 176 to 191 of the full-length HGH molecule's C-terminus-this region has been shown to be the smallest functional unit for HGH to bind to specific sites on adipocytes, exerting its anti-lipogenesis and lipolytic effects.
Physical Mechanism:
It acts directly on the GH binding site on the adipocyte membrane (non-classical GH receptor, does not activate the JAK2-STAT pathway).
It activates hormone-sensitive lipase (HSL) in adipocytes, promoting the breakdown of triglycerides into free fatty acids for excretion.
It inhibits lipoprotein lipase (LPL) activity → reducing the reuptake and storage of circulating triglycerides by adipocytes.
It does not stimulate IGF-1 production or activate downstream GH receptor signaling → thus lacking the systemic anabolic effects, blood glucose interference, and bone/soft tissue hyperplasia effects of HGH.
In short: It only takes the small portion of HGH that "helps break down fat and prevents new fat from entering," discarding the rest.
Does not increase IGF-1: Does not negatively suppress the pituitary gland, avoiding the risk of acromegaly and visceral enlargement.
Glycemic Friendly: Does not affect insulin sensitivity; insulin resistance/hyperglycemia caused by HGH does not occur.
No Systemic Anabolic Effects: Suitable for those who want to target fat specifically without the water and sodium retention or carpal tunnel syndrome caused by HGH.
Extremely Small Molecular Weight: Rapid subcutaneous absorption; freeze-dried peptides are easy to store and transport.
Impressive Animal Experiments: Obese mouse models show significant reduction in visceral and subcutaneous fat, with effects approaching those of the lipolysis fraction of an equivalent amount of HGH.
Weak Evidence for Human Fat Reduction: Shares the fate of AOD9604-effective in animals, but its independent fat reduction efficacy in humans has not been proven superior to placebo in RCTs. Large-scale clinical trials failed before studies shifted to joint-related areas (AOD9604), unlike HGH. Frag has never been approved for any indication.
Common local irritation: Redness, swelling, itching, and occasional mild burning sensation at the injection site. Short peptides easily induce the release of local inflammatory mediators.
Dose-effect ambiguity: There is no authoritative consensus on the effective dose range for humans. The commonly circulated 500-1000 μg/day divided doses are based on forum experience rather than clinical practice.
No muscle gain: Don't expect it to replace HGH for anabolism promotion or recovery; it's purely a lipid metabolism regulator.
Significant batch-to-batch variation: The purity and sequence accuracy of unregistered raw materials are inconsistent (whether it's truly 176-191 or fully HGH-cleaved impurities).
In conjunction with a strict diet and training regimen, as a metabolic peptide to assist in reducing stubborn localized fat (lower abdomen/back and waist) (low expected management level).
For researchers or advanced enthusiasts who want to experience the lipolysis effect of GH but are concerned about its impact on blood sugar/IGF-1/water retention.
Research Uses: Localization of GH lipolysis functional domains, research on GH binding sites in adipocytes, in vitro models of lipid metabolism.
Not a substitute for weight loss drugs, not for the treatment of obesity.
Absolute Contraindications: Allergy to peptides, history of malignant tumors (theoretically, there is controversy regarding its effect on the tumor microenvironment through promoting adipocyte metabolism; avoid for safety reasons), pregnant or breastfeeding women, minors.
WADA Status: Belongs to growth hormone-related fragments and is listed on the World Anti-Doping Agency's prohibited list-prohibited for participating athletes.
Reconstitution Recommendation: 10mg/vial plus 1-2mL of antibacterial water containing 0.1% acetic acid → concentration 5-10mg/mL, gently roll, do not vortex vigorously. Literature/forums typically recommend a subcutaneous dose of 300-1000 μg twice daily (morning + before exercise), but this is empirical usage without clinical endorsement.
Storage Notes: Store at low temperature for a short period after reconstitution; discard immediately if cloudy or discolored; lyophilized powder clumping upon contact with moisture indicates degradation.
Ingredient Warning: Commercially available products are unregistered and labeled "For Research Use Only." Always check the Certificate of Authorization (COA) before purchasing (HPLC+MS confirmation of 176-191 hexapeptide, not a mixture of all HGH fragments). Counterfeit products are common.
Expectations Management: Relying solely on it for "effortless weight loss" is likely to be disappointing. It's best used as a supplementary component of a strict weight loss program, not the main ingredient.
In short: HGH 176-191 fragment is the smallest active fragment for HGH lipolysis, with a wide safety window and no impact on IGF-1 or blood sugar. However, its efficacy for weight loss in humans alone lacks strong evidence-it's essentially related to AOD9604. Animal data looks good, but expectations for human use should be lowered; it only has some effect when combined with diet and exercise.
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