Fragment 176-191 — a peptide studied for fat metabolism and growth hormone–related effects.
Also known as: HGH Fragment
Fragment 176-191, sometimes called HGH Fragment, is a short synthetic peptide derived from the C-terminal region of human growth hormone — specifically the last sixteen amino acids of the full hormone. Researchers isolated this region after discovering that the fat-mobilizing activity of growth hormone appears to be concentrated in its tail end, while the muscle-building and blood-sugar-raising activities are distributed elsewhere along the molecule.
The interest in Fragment 176-191 comes from this apparent separation of functions. By using only the C-terminal fragment, researchers hoped to capture the lipolytic — fat-breakdown — effects of growth hormone without triggering the full hormonal cascade. Early structure-activity work mapped out exactly which residues were required for biological activity and showed that the peptide needed to be in the correct three-dimensional configuration to work at all.
More recent investigations have moved in unexpected directions, including the use of Fragment 176-191 as a targeting peptide in cancer-drug delivery systems. It remains one of the more frequently discussed growth-hormone-derived peptides in performance and physique communities, though the published research base is narrower than its popularity suggests.
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The foundational work on Fragment 176-191 dates to the late 1970s, when researchers synthesized a series of C-terminal fragments of human growth hormone to identify which portion of the molecule was responsible for specific biological effects. A 1978 study tested six overlapping peptides spanning residues 172-191 through 180-191 and found that activity required at minimum the sequence from residue 178 onward — fragments shorter than this were inert (2).
The biologically active peptides, including Fragment 176-191, produced a short-lived rise in blood glucose followed by a more sustained increase in circulating insulin. They also reduced insulin sensitivity in tolerance testing. This is notable because it tracks with one of the known actions of intact growth hormone, suggesting the C-terminal region carries the hormone's effects on glucose and insulin handling rather than only its fat-mobilizing properties as is sometimes claimed (2).
The same study also established a structural principle that has held up: biological activity requires not just the right amino acid sequence but the correct physical configuration. Fragments with the right residues but the wrong folding were inactive. This helps explain why synthetic Fragment 176-191 quality varies considerably depending on how it's manufactured and stored.
A more recent and unexpected line of research has explored Fragment 176-191 as a targeting component in cancer drug delivery. A 2022 study loaded chitosan nanoparticles with both doxorubicin — a widely used chemotherapy agent — and Fragment 176-191, then tested the dual-loaded particles against MCF-7 breast cancer cells (1).
The rationale comes from the fact that many cancer cells overexpress growth hormone receptors, which means peptide fragments derived from growth hormone may preferentially bind to tumor tissue. Molecular docking simulations suggested that Fragment 176-191 enhances doxorubicin's binding affinity to several breast cancer protein targets, essentially acting as a chemical chaperone that helps the chemotherapy drug attach more strongly where it's needed (1).
In cell viability testing, the dual-loaded nanoparticles showed greater anti-proliferative activity against breast cancer cells than doxorubicin-loaded particles without the peptide. The dual particles also had favorable physical characteristics — size, charge, and dispersion — suggesting they could work as a delivery vehicle. This is early laboratory work rather than clinical evidence, but it points to a potential role for Fragment 176-191 well outside its original metabolic context (1).
Fragment 176-191 has developed a substantial reputation in fitness and physique communities as a fat-loss peptide, based largely on the original observation that the C-terminal region of growth hormone carries its lipolytic activity. A 2026 critical review of peptide use in sport and bodybuilding names Fragment 176-191 explicitly among the synthetic fragments promoted for fat metabolism (3).
The review notes that the published clinical evidence supporting peptide use for performance or body composition purposes is limited, with most controlled studies examining therapeutic rather than physique-oriented dosing. The authors also flag that supraphysiological dosing protocols common in bodybuilding communities carry potential metabolic risks, including effects on insulin sensitivity — which aligns with the insulin-related findings from the original 1978 structure-activity work (2, 3).
Fragment 176-191 has not been formally banned by major anti-doping authorities as a named substance, but the review notes that growth-hormone-related peptides generally face increasing scrutiny from detection programs, and that the unregulated supply chain for peptides marketed online creates additional uncertainty about what users are actually receiving (3).
Reported adverse effects specific to Fragment 176-191 in the published research are minimal, though the body of evidence is narrow. The original structure-activity work noted that biologically active C-terminal fragments reduced insulin sensitivity and produced short-lived rises in blood glucose, which is worth keeping in mind for anyone with existing metabolic concerns (2). The 2026 sport-medicine review flags general risks associated with peptide use including cardiovascular strain, insulin resistance, and supply-chain issues where products may be mislabeled or contaminated (3).
The body of Fragment 176-191 evidence comes primarily from preclinical and laboratory work, with no substantial human clinical data available.
Fragment 176-191 falls within the broader category of growth-hormone-related peptides that face increasing attention from anti-doping authorities — relevant context for competitive athletes.
All information on this site is for research and educational purposes only. The compounds discussed are not approved by the FDA and are not intended to diagnose, treat, cure, or prevent any disease.