HGH Fragment 176-191 Explained: The Fat-Burning Tail of Growth Hormone

HGH Fragment 176-191, often shortened to HGH frag, is the last 16 amino acids of the 191-amino-acid growth hormone molecule. That small tail is the part tied to growth hormone's effects on fat. The rest of the molecule, which drives growth signals and IGF-1, is left out. That split is why the fragment keeps turning up in fat-metabolism research.

This guide covers what the peptide is, what the studies actually found, the molecular data that matter, and how it compares with AOD-9604 and full HGH 191AA. Everything here is for research and laboratory use only.

Key Takeaways

• HGH Fragment 176-191 is the tail end of human growth hormone (amino acids 176 to 191): a 16-amino-acid peptide with the sequence Phe-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe.
• CAS number 66004-57-7, formula C78H123N23O22S2, molecular weight about 1799 g/mol (a little more as the acetate salt).
• In animal studies, this region of growth hormone cut fat gain and raised fat burning without acting on the growth hormone receptor, and without the rises in IGF-1, insulin or blood sugar that full HGH brings.
• AOD-9604 is a close relative (amino acids 177 to 191 with a tyrosine added), with the larger research record, including human trials.
• Full HGH 191AA is the whole hormone, with both the fat and the growth parts, so it behaves very differently from the fragment.
• Lyze Labs supplies HGH Fragment 176-191 third-party HPLC tested at 99%+ purity with a published COA, shipped free and discreetly worldwide in 7 to 14 days.

What Is HGH Fragment 176-191?

Human growth hormone is a single chain of 191 amino acids made by the pituitary gland. Decades of work showed that its many effects are not spread evenly along the chain. The effect on fat sits near the tail end, while the parts that drive cell growth and IGF-1 sit elsewhere. HGH Fragment 176-191 takes that tail, amino acids 176 to 191, as a short lab-made peptide.

The fragment does not act on the growth hormone receptor, so studying it shows growth hormone's fat effects without the rest of the hormone's signals (Heffernan, 2001). That is why it is grouped with peptides studied for fat metabolism rather than with growth compounds like HGH 191AA. It is a targeted tool, not a hormone replacement.

In the lab it arrives as a freeze-dried white powder, sensitive to heat and to repeated freezing and thawing. Handling matters for the data; see the peptide storage and stability guide.

Mechanism of Action in Research Models

The evidence here deserves care, because a lot of what is said online goes beyond it. Here is what the published studies found:

• It blocks fat formation. In rats, the 177-191 part of growth hormone blocked new fat formation (lipogenesis) as strongly as the whole hormone did. In that study it did not measurably raise fat breakdown in fat tissue (Wu, 1993).
• It raises fat burning in obese mice. AOD-9604, the close relative, cut weight gain in obese mice, raised fat burning (fat oxidation) and raised glycerol in the blood, a sign of fat breakdown (Heffernan, 2001).
• Beta-3 receptors are involved, but not as the direct target. Growth hormone and AOD-9604 both raised the number of beta-3 adrenergic receptors in fat, the main fat-releasing receptor. In mice without beta-3 receptors, long-term treatment lost its effect on weight. But the authors concluded the fat effects do not run directly through beta-3 receptors (Heffernan, 2001). Claims that the fragment simply "binds beta-3 receptors" go further than the data.

Most of this work used AOD-9604 or the 177-191 piece, not the 176-191 fragment itself, and the fragment has few dedicated studies of its own. Treat it as a promising lab and animal-model tool for fat metabolism, not a proven human treatment.

The IGF-1 and Glucose Question

The main reason researchers care about this fragment is what it does not do. Full growth hormone raises blood sugar and drives IGF-1, and those effects come mostly from other parts of the hormone, not the tail.

Because the tail does not act on the growth hormone receptor, studies of this region found fat effects without the growth hormone receptor's downstream signals. In obese rats, AOD-9604 cut weight gain without harming insulin sensitivity (Ng, 2000). For researchers, that is the appeal: a way to study fat metabolism without the blood sugar and growth factor effects that complicate full HGH experiments. It also sets the fragment apart from the GLP-1 class compounds.

HGH Fragment 176-191 vs AOD-9604 vs HGH 191AA

The three are often confused because they share a family tree. The table sets them apart.

AOD-9604 comes from the same tail of growth hormone, with a tyrosine added to the front. It has the longer research history, including human trials for obesity, though those trials did not lead to approval as a weight-loss drug. HGH 191AA is the whole hormone and brings all the growth and blood sugar effects the fragment leaves out. The right choice depends on the research question. All three are available: HGH Fragment 176-191, AOD-9604 and HGH 191AA.

Molecular Profile and Reconstitution

For accurate lab work, the identity data should match the COA exactly.

The peptide is mixed with bacteriostatic water and kept cold once in solution, since a short peptide like this breaks down over time. The guide to reconstituting research peptides covers the method step by step. It lasts only a short time in the blood in animal models, so careful handling and accurate measuring matter for reliable results.

Sourcing and Purity Verification

A fat-metabolism peptide is only as good as the molecule in the vial. Mislabeled or impure material is the fastest way to ruin a dataset, and the unregulated end of this market is full of it. That is why every batch of HGH Fragment 176-191 from Lyze Labs is third-party HPLC tested and shipped with a published certificate of analysis confirming 99%+ purity. Identity and purity should always be verified before any research begins, a process detailed in our COA and purity verification guide.

Lyze Labs is trusted by researchers in 150+ countries, with 10,000+ orders shipped. Each kit is ten 5 mg vials from one batch. Orders paid before the daily batch closes are processed that day, shipping is free and tracked, most orders arrive in 7 to 14 days, and delivery is guaranteed. You can pay by Visa, Mastercard, Amex, PayPal, Apple Pay, Google Pay, bank transfer, local wallets and bank apps in your region, or crypto (USDT, USDC, BTC). New to ordering research compounds from abroad? Read the international peptide shipping guide first.

Frequently Asked Questions

What is HGH Fragment 176-191 used for in research?

It is used in lab and animal models to study fat metabolism: blocking new fat formation and raising fat burning. Researchers value it because it carries growth hormone's fat effects without acting on the growth hormone receptor. It is supplied for research and laboratory use only and is not for human use.

How is HGH frag 176-191 different from full HGH 191AA?

HGH 191AA is the complete 191-amino-acid growth hormone, about 22,100 g/mol, with both growth and fat effects. HGH Fragment 176-191 is only the last 16 amino acids, about 1799 g/mol, and it does not act on the growth hormone receptor, so in research models it lacks the IGF-1 and blood sugar effects of the full hormone. The fragment is a targeted tool; full HGH affects the whole growth hormone system.

Does HGH 176-191 affect IGF-1 or blood glucose?

Not in the way full growth hormone does. This tail region does not act on the growth hormone receptor, and in obese rats its relative AOD-9604 cut weight gain without harming insulin sensitivity. The IGF-1 and blood sugar effects of growth hormone come from other parts of the molecule.

Is HGH Fragment 176-191 better than AOD-9604?

Neither is better everywhere. AOD-9604 is the same tail with a tyrosine added, and it has the larger research record, including human trials. HGH Fragment 176-191 is the plain fragment, with few studies of its own. Researchers weigh AOD-9604's evidence against the fragment's simplicity and cost.

What is the CAS number and molecular weight of HGH Fragment 176-191?

The CAS number is 66004-57-7, the molecular formula is C78H123N23O22S2, and the free-base molecular weight is approximately 1799 g/mol, with the acetate salt form running slightly higher. These values should match the certificate of analysis supplied with any research-grade batch. Always confirm identity data against the COA before beginning work.

How can I verify HGH frag 176-191 purity before ordering?

Reputable suppliers provide a third-party HPLC certificate of analysis showing purity, identity, and batch number. Lyze Labs publishes a COA confirming 99%+ purity for every HGH Fragment 176-191 batch and supports batch verification on request. Reviewing the COA and checking for HPLC and mass spectrometry data is the single most reliable step, as outlined in our peptide purity verification guide.

Order Research-Grade HGH Fragment 176-191

For researchers who need verified, HPLC-tested material with a published COA at 99%+ purity, HGH Fragment 176-191 is in stock now with free discreet worldwide shipping in 7 to 14 days. A person confirms your order and sends payment options, day or night.

Studies Cited

• Wu Z, Ng FM (1993). Antilipogenic action of synthetic C-terminal sequence 177-191 of human growth hormone. Biochemistry and Molecular Biology International.
• Ng FM, et al. (2000). Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone. Hormone Research.
• Heffernan MA, et al. (2001). Increase of fat oxidation and weight loss in obese mice caused by chronic treatment with human growth hormone or a modified C-terminal fragment. International Journal of Obesity.
• Heffernan M, et al. (2001). The effects of human GH and its lipolytic fragment (AOD9604) on lipid metabolism following chronic treatment in obese mice and beta3-AR knock-out mice. Endocrinology.