HGH Fragment 176-191 is the final 16-amino-acid stretch of the human growth hormone molecule, corresponding to the part associated with fat breakdown. Unlike full growth hormone it lacks the receptor-binding regions, so it does not raise IGF-1 and produces no anabolic effect.
In mouse studies it reduced fat tissue, but the only published human trial found no significant difference. Where this peptide sits among the molecules that affect body weight is described in the pillar article on GLP-1 and incretins.
What is HGH Fragment 176-191?
The human growth hormone molecule consists of 191 amino acids. HGH Fragment 176-191 is its last 16 amino acids, the terminal stretch known as the lipolytic domain. That fragment on its own retains part of the growth hormone activity linked to fat breakdown and loses the remaining functions. It is traded as research material.
The idea behind the molecule is simple: take from growth hormone only the part responsible for burning fat and leave the rest. The same idea produced a modified version called AOD9604, developed as a candidate anti-obesity drug.
How does it differ from full growth hormone?
Full growth hormone binds to its receptor and triggers the pathway that leads to IGF-1 production in the liver. HGH Fragment 176-191 lacks the regions needed to bind the receptor, so it does not raise IGF-1 and gives neither the anabolic effect nor the effect on glucose metabolism typical of the complete molecule. What remains is the effect on fat metabolism alone.
That difference translates into expectations. The fragment is not a weaker version of growth hormone or a substitute for it. It is a separate molecule, from which no gain in muscle mass, no increase in strength and no action on connective tissue should be expected. Peptides that act on the growth hormone axis in a different way are covered in the article on growth hormone peptides.
What did the studies show?
In obese mice the fragment reduced fat tissue by 12 to 23 per cent. In humans the result was different. In the only published clinical trial, at a dose of 300 micrograms twice a day, no statistically significant difference was found between the groups in weight loss, body composition or metabolic parameters.
The modified version, AOD9604, went through wider clinical development but failed to meet the primary endpoint of its phase 2b trial. In 2007 the United States Food and Drug Administration rejected the marketing application. Clinical development of the molecule effectively ceased, and since then no study has appeared that would change this picture.
Why did the mouse result not repeat in humans?
That kind of divergence is the rule in obesity research, not the exception. An animal model is a simplification: the animals have a different hormonal balance, receive an identical diet and are observed for a short time. A human being lives in conditions no model reproduces.
There is also the question of effect size. A reduction in fat tissue of a dozen or so per cent in mice does not mean a dozen or so per cent in a human, because the baseline and the method of measurement are different. A review of peptides used in sport and injury, published in Sports Medicine in 2026, puts it plainly: many unapproved peptides look promising in animal models, while sound human safety data are scarce.
What is the status of HGH Fragment 176-191 in sport?
The modified version AOD9604 is on the prohibited list of the World Anti-Doping Agency in category S0, which covers substances not approved for human use. The agency confirmed this in a statement in 2013, noting that the ban has applied since 2011.
Category S0 operates regardless of whether a substance improves performance. It is enough that no authority has approved it for human use. That category is covered more broadly in the article on the ban on BPC-157 and TB-500 in sport.
Why does the solution lose potency quickly?
Once dissolved, the fragment undergoes predictable chemical breakdown, through deamidation and oxidation among other routes. Users report a drop in effectiveness after roughly two weeks of storage in a fridge. That is shorter than for many other peptides.
For this reason, storage conditions are worth watching particularly closely with this molecule: cold, darkness and no shaking. The rules for lyophilised powder and for the finished solution are collected in the article on storing peptides, and dissolving itself is described in the article on reconstituting a peptide.
What is its legal status and what is in the shop?
The fragment is not an approved medicine and remains a research compound. Clinical development effectively stopped after the failure of AOD9604, and the molecule has never been approved for any indication. The status of the whole group is set out in the article on the legal status of peptides.
In this shop it appears strictly as research material, in three variants from three manufacturers, listed on the HGH Fragment 176-191 page. The other molecules linked to body weight are collected in the weight loss peptides category. The terms of purchase are set out on the legal warning page.
Frequently asked questions
Does HGH Fragment 176-191 raise IGF-1?
It does not. The fragment lacks the receptor-binding regions through which full growth hormone triggers IGF-1 production.
Does the fragment work for weight loss in humans?
The only published clinical trial found no significant difference in weight loss or body composition. The data on fat reduction come from studies in mice.
Does the fragment build muscle mass?
No. Without binding the growth hormone receptor there is no rise in IGF-1, and that is the pathway responsible for the anabolic action of the complete molecule.
Why does an HGH Fragment solution spoil quickly?
It undergoes chemical breakdown through deamidation and oxidation. Users report a drop in effectiveness after roughly two weeks in a fridge.
Is AOD9604 banned in sport?
Yes. The World Anti-Doping Agency places AOD9604 in category S0, substances not approved for human use, and has stated that the ban has applied since 2011.
Is HGH Fragment 176-191 an approved medicine?
It is not. The modified version AOD9604 was never approved, and its application was rejected by the United States Food and Drug Administration in 2007.
Where this information comes from
The structure of the fragment, the absence of an effect on IGF-1, the mouse data (12 to 23 per cent) and the result of the only human trial come from material published by FormBlends, version of 30 May 2026. The same material gives the failure of AOD9604 in the phase 2b trial, the rejection of the application by the FDA in 2007, the stability problems of the solution and the research-compound status. The page was checked on 31 August 2026.
The S0 status of AOD9604 and the statement that the ban has applied since 2011 come from the World Anti-Doping Agency statement on that substance, published on wada-ama.org. The sentence about animal data outweighing human safety data comes from the review by Mendias CL and Awan TM, “Safety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance”, Sports Medicine 2026, PMID 41966639, read through Europe PMC. These pages were checked on 7 September 2026.