What is HGH frag 176-191?
HGH fragment 176-191 is the last 16 amino acids of human growth hormone, sold as a research peptide for fat loss. The fragment itself has never been tested in people, and data on this exact sequence come from animal studies. The fat-loss claims borrow from the closely related AOD-9604, which failed in a trial of 502 adults with obesity. The fragment is not authorised as a medicine anywhere, and sport bans it at all times.
At a glance
- What it is
- Residues 176-191 of human growth hormone: 16 amino acids (FLRIVQCRSVEGSCGF), one disulfide bridge
- Status in the EU
- Not authorised as a medicine in the EU or any other country; research material only
- Status in the US
- Not approved; FDA advisers voted 12–0 against compounding its analogue AOD-9604 (2024)
- Research
- Rat and mouse studies, mostly of related fragments; no human study of this exact peptide
- Sport
- Prohibited at all times; named in WADA class S2.2.3 (growth hormone fragments)
- Human evidence
- Animal data only; the analogue AOD-9604 failed in human trials
HGH frag 176-191 dosage snapshot
- Route
- subQ
- Dose range
- 250-500 mcg
- Frequency
- daily
- Duration
- 8-12 weeks
Based on reported research sources; not a dosing instruction.
Origin and structure
Human growth hormone is a chain of 191 amino acids. HGH fragment 176-191 is its last 16: Phe-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe, with a disulfide bridge between the two cysteines that closes part of the chain into a loop. Its formula is C78H123N23O22S2 and its molar mass 1,799.1 g/mol (CAS 66004-57-7).
The idea that separate pieces of growth hormone carry separate effects comes from a long Australian line of research. In the 1970s Frank Ng, J. Bornstein and colleagues tested a series of synthetic fragments from the end of the hormone (172-191, 176-191, 177-191 and shorter ones) for effects on blood sugar and insulin. In the 1990s Ng's group at Monash University in Melbourne recast the 177-191 piece as the hormone's fat-regulating domain. Adding a tyrosine to its front end gave AOD-9604, which the Australian company Metabolic Pharmaceuticals took into human trials for obesity.
The unmodified 176-191 fragment has never been tested in a human trial. It circulates as a research chemical, under a name that is often used loosely (see the comparison below).
How it is thought to work
The case for the fragment is an argument by division: if the end of the growth hormone chain carries the hormone's action on fat tissue on its own, a short piece of it might reproduce that action while leaving growth and blood sugar alone. The supporting data come from neighbouring peptides, not from 176-191 itself. In rat fat tissue, hGH 177-191 blocked the formation of new fat as strongly as intact growth hormone but did not increase fat breakdown (Wu and Ng, 1993). In obese mice, AOD-9604 increased fat breakdown and fat burning, and in cell tests it did not bind the growth-hormone receptor or make cells divide (Heffernan et al., 2001).
For 176-191 itself the evidence points the other way: in the 1978 rat study it briefly raised blood glucose and insulin, the insulin-opposing effect typical of growth hormone. Studies of AOD-9604 in obese rats and mice, lasting 14 to 19 days, reported no loss of insulin sensitivity and no rise in blood sugar, and in the AOD-9604 human trials IGF-1 and glucose tolerance did not change. No study has measured how long either peptide lasts in the human body; the FDA found no human pharmacokinetic data for AOD-9604.
Is HGH fragment 176-191 approved?
No. No medicines regulator has authorised it, in the EU or elsewhere. In the Netherlands it is not a registered medicine, so it may not be sold or promoted for use in people; it is available only as research material.
In the United States it is not an approved drug either. The FDA has looked at its closest relative instead. In a 2024 review of AOD-9604 for pharmacy compounding, the agency found a lack of evidence that it works for obesity, no human data at all for injection under the skin, and possible safety signals in animal studies. On 4 December 2024 the FDA's Pharmacy Compounding Advisory Committee voted 12 to 0 against adding AOD-9604 to the list of substances US pharmacies may compound.
In sport it is prohibited at all times. The WADA Prohibited List for 2026 names hGH 176-191 and AOD-9604 as examples of growth hormone fragments in class S2.2.3, as non-specified substances. The 2026 list was published in the Dutch Tractatenblad and has applied in the Netherlands since 1 January 2026.
What the research shows
The record falls into three parts: one old rat study of the exact sequence, rodent studies of its neighbours, and human trials of AOD-9604. The human trials were all funded by the developer and run in Australia between 2001 and 2006, and their efficacy results were never published in full. No trial of hGH 176-191 or AOD-9604 is registered on ClinicalTrials.gov.
- hGH 176-191 itself (Ng and Bornstein, 1978): given to normal rats, 176-191, like 172-191, 177-191 and 178-191, caused a short rise in blood glucose and a longer rise in insulin; the shorter 179-191 and 180-191 were inactive. Fragments containing residues 178-191 also reduced insulin sensitivity.
- hGH 177-191 in rats (Wu and Ng, 1993): it blocked fat formation in fat tissue as strongly as intact growth hormone, without a significant effect on fat breakdown.
- AOD-9604 in rodents (2000-2001): given by mouth for 19 days, it held weight gain in obese Zucker rats to 15.8 g against 35.6 g in controls, less than half, without the loss of insulin sensitivity seen with intact growth hormone. In obese mice, 14 days of infusion reduced weight gain and raised fat burning.
- AOD-9604 in people, short studies: four small placebo-controlled studies in 15 to 36 men gave single intravenous or oral doses or one week of oral dosing. According to the FDA's summary, the three that looked at weight found no significant loss against placebo.
- AOD-9604, 12-week trial (METAOD005): 300 adults with obesity took 1, 5, 10, 20 or 30 mg by mouth daily, or placebo. A 2005 conference abstract reported about 0.22 kg of weight loss a week on 1 mg against 0.07 kg on placebo, with the largest effect at the lowest dose. The full results were never published, and the FDA called the differences small and of unclear meaning.
- AOD-9604, 24-week trial (METAOD006): 536 adults with obesity enrolled and 502 were randomised to 0.25, 0.5 or 1 mg tablets daily or placebo, alongside a supervised diet and exercise programme. Weight loss at 12 weeks, the primary endpoint, and at 24 weeks did not differ significantly from placebo, and on 21 February 2007 Metabolic Pharmaceuticals ended development for obesity.
HGH fragment 176-191 versus AOD-9604
The two differ by a single amino acid. The natural 176-191 fragment starts with phenylalanine. AOD-9604 is residues 177-191 with a tyrosine added to the front, which its developers described as stabilising the peptide: YLRIVQCRSVEGSCGF, 1,815.1 g/mol. Nearly all the research, animal and human, used AOD-9604 or the bare 177-191 piece, and its results are often attributed to 176-191.
The names are used loosely, even in journals. A 2022 cell study with hGH fragment 176-191 in its title gives the tyrosine sequence of AOD-9604 for the peptide it modelled, and a 2026 review in Frontiers in Endocrinology lists AOD9604 as "hGH 176-191". WADA names them as two separate examples. What tells them apart is the sequence and the measured mass: about 1,799 g/mol for the natural fragment, about 1,815 g/mol for AOD-9604.
Neither has shown a benefit in people. AOD-9604 at least has safety data from six controlled trials; the unmodified fragment has none.
Potential benefits
- Less fat formation in rat fat tissue, as hGH 177-191 (animals)
- Less weight gain in obese rats and mice, as AOD-9604 (animals)
- Weight loss in obesity, as AOD-9604: trials found no significant effect
- The unmodified fragment: never studied in humans
Safety profile
Unknown risk- CautionNo human safety data exist for the unmodified fragment. In the 1978 rat study it briefly raised blood glucose and insulin.
- CommonIn six placebo-controlled trials of the related peptide AOD-9604 (893 participants, oral or intravenous, up to 24 weeks), headache was the most common adverse event and adverse events were about as frequent as on placebo; IGF-1 and glucose tolerance did not change, and no antibodies against the peptide were found.
- Less commonIn one intravenous AOD-9604 study, 5 of 23 men reported mild to moderate euphoria while on the peptide and none on placebo; one had severe chest tightness judged possibly related.
- SeriousIn the 12-week AOD-9604 trial, five people on the peptide and none on placebo had a serious adverse event, four of them cancers (three of the skin, one of the breast). The investigators judged none related, but a trial of 300 people over 12 weeks cannot settle the question.
- CautionThe FDA's 2024 review of AOD-9604 noted possible bone effects in rats and possible liver toxicity in monkeys in oral toxicity studies, equivocal genotoxicity results, and a risk of immune reactions from aggregates and impurities in injectable products.
Frequently asked questions
- Is HGH fragment 176-191 legal in the Netherlands?
- It is not a registered medicine in the Netherlands or anywhere else, so it may not be sold, advertised or supplied for use in people. Buying and selling it as research material is a different status, which our guide on research-use-only products in the Netherlands explains. For athletes under anti-doping rules it is prohibited regardless of how it was obtained.
- Is HGH fragment 176-191 the same as AOD-9604?
- Almost, but not quite. The natural fragment starts with phenylalanine; AOD-9604 has a tyrosine in that position (residues 177-191 plus an added tyrosine). Their masses differ by 16 g/mol, about 1,799 versus 1,815. The names are often mixed up, even in published papers, so only the sequence shows which one a sample is. Almost all the research was done with AOD-9604.
- Does HGH fragment 176-191 burn fat?
- That has never been tested in people. The fat-loss idea comes from rodent studies of the related peptides hGH 177-191 and AOD-9604, which reduced weight gain in obese rats and mice. When AOD-9604 was tested in people, a 24-week trial in 502 adults with obesity found no significant weight loss against placebo, and the developer abandoned it for obesity in 2007.
- Does it raise IGF-1 or blood sugar like growth hormone?
- For the fragment itself there are no human data. In a 1978 rat study of this exact sequence, it briefly raised blood glucose and insulin. In the human trials of AOD-9604, IGF-1 and glucose tolerance did not change over 12 to 24 weeks, but those results apply to AOD-9604 taken by mouth, not to an injected fragment.
- Is HGH fragment 176-191 banned in sport?
- Yes, at all times, in and out of competition. The 2026 WADA Prohibited List names hGH 176-191 and AOD-9604 in class S2.2.3, growth hormone fragments, as non-specified substances. The list has applied in the Netherlands since 1 January 2026. See our guide on peptides and the doping list.
Storage and handling
Store according to product-label instructions and batch handling notes. Lyophilized research peptides are commonly kept dry, protected from light, and handled with clean laboratory technique.
References
Checked against these sources on 28 October 2026.