Search for HGH Fragment 176-191 and you will find animal fat-loss data, a human clinical programme, and a finding that it does not affect blood sugar. None of that belongs to it. All of it belongs to AOD-9604, a different molecule.
The two differ by one amino acid and 16 daltons. AOD-9604 was developed at Monash University and taken through six placebo-controlled human trials; the unmodified fragment has no human research of its own, and the only original studies ever conducted on it reported a hyperglycaemic action — the opposite of the claim usually made for it. This article separates them, inside the weight loss and metabolic peptides category.
What is the difference between HGH Fragment 176-191 and AOD-9604?
One oxygen atom and sixteen daltons. HGH Fragment 176-191 is the native hGH(176–191) sequence beginning with phenylalanine — CAS 66004-57-7, 1,799.08 Da. AOD-9604 is Tyr-hGH177-191, the same region with that phenylalanine swapped for tyrosine — CAS 221231-10-3, 1,815.08 Da. Both carry a Cys7–Cys14 disulfide. The tyrosine was added deliberately, for stability and to allow radioiodination in binding assays. That single substitution separates a molecule with six human trials from one with none.
HGH Fragment 176–191 | AOD-9604 | |
|---|---|---|
First residue | Phe (native — residue 176 of hGH) | Tyr (substituted) |
Formal name | hGH(176–191) | Tyr-hGH177-191 |
CAS | 66004-57-7 | 221231-10-3 |
Formula | C₇₈H₁₂₃N₂₃O₂₂S₂ | C₇₈H₁₂₃N₂₃O₂₃S₂ |
Molecular weight | 1,799.08 Da | 1,815.08 Da |
Disulfide | Cys7–Cys14 | Cys7–Cys14 |
Human trials | None | Six, ~893 subjects |
Residue 176 of mature human growth hormone is phenylalanine, verifiable directly from the UniProt P01241 sequence, whose mature chain ends ...VETF·LRIVQCRSVEGSCGF. The compound page is HGH Fragment 176-191.
One extra oxygen atom. Sixteen daltons. That is the entire chemical difference, and it separates a molecule with a full clinical programme from one with essentially no research at all.
What did AOD-9604's human trials actually find?
AOD-9604 was tested properly and did not work well enough to develop. Stier et al. (2013) documents six randomised, double-blind, placebo-controlled trials — roughly 893 subjects, from a Phase 1 intravenous study of 15 people to Phase 2b trials of 300 and 502 participants — with safety described as indistinguishable from placebo. A 12-week trial produced 1.8 kg more weight loss than placebo. The programme was discontinued in 2007.
Study | What it tested | Population | Result |
|---|---|---|---|
Ng et al. (Hormone Research, 2000) | AOD-9604 500 µg/kg/day orally, 19 days | Obese Zucker rats (animal) | More than a 50% reduction in body-weight gain |
Stier et al. (J Endocrinol Metab, 2013) | Six randomised, double-blind, placebo-controlled trials | Phase 1 IV n=15 through Phase 2b n=300 and n=502; ~893 total | Safety indistinguishable from placebo |
12-week trial (within that programme) | AOD-9604 vs placebo | Adults with obesity (human RCT) | 1.8 kg more weight loss than placebo |
24-week trial (within that programme) | AOD-9604 vs placebo | Adults with obesity (human RCT) | Poor efficacy — development halted |
The Monash group, led by Frank Ng, developed AOD-9604 to isolate growth hormone's lipolytic signal from its growth-promoting and glucose-affecting actions. The preclinical work is real, and so is the outcome. As an independent review put it, "after a phase IIB clinical trial, the results did not support the commercial viability of the drug as a treatment for obesity" (Pharmaceuticals, 2010).
That is the honest headline for this compound class: the molecule with human data was tested properly, and it did not work well enough to develop.
What does the unmodified fragment's own literature say?
It reports the opposite of the claim usually made for it. A PubMed search for the native fragment returns six records, none a human efficacy trial, and the earliest original work describes a hyperglycaemic action — "Hyperglycemic action of synthetic C-terminal fragments of human growth hormone" (American Journal of Physiology, 1978) and a follow-up mechanism paper in Biochimica et Biophysica Acta (1982). The confident "no impact on blood glucose" claim is AOD-9604's trial finding, not the fragment's.
That is not a subtle distinction for anyone with impaired glucose tolerance. The marketing takes a reassurance generated in human trials of one molecule and applies it to a second molecule whose own small literature points the other way.
Does HGH Fragment 176-191 work through a β-adrenergic mechanism?
No — the researchers who studied it ruled that out. The common explanation holds that the fragment acts through β-adrenergic-like signalling: cAMP, hormone-sensitive lipase, free fatty acid release. Heffernan et al. (Endocrinology, 2001) concluded that "the lipolytic actions of both hGH and AOD9604 are not mediated directly through the beta(3)-AR". The standard mechanism story therefore describes a pathway the original investigators specifically excluded, for a molecule they were not studying.
Both faults compound. A mechanism explanation is supposed to be the part of a product description that is hardest to fake, because it has to connect to a literature. Here it connects to a literature that says no.
Which HGH Fragment 176-191 claims belong to another molecule?
Six of ten. Of the ten claims routinely made for HGH Fragment 176-191, six describe results that belong to AOD-9604 — the animal fat-loss data, the glucose neutrality, the IGF-1 finding, the six safety trials, the human weight loss, and the tyrosine substitution itself. Three have no source in either compound's literature. One, glucose neutrality for the native fragment, is contradicted by the fragment's own papers.
Claim | Evidence | Verdict — whose result is this? |
|---|---|---|
Reduces visceral fat in obese animals | Real — 500 µg/kg/day oral, 19 days | AOD-9604 |
Does not raise blood glucose | Demonstrated in human trials | AOD-9604 |
Does not raise IGF-1 | Demonstrated | AOD-9604 |
Six human safety trials | Real — ~893 subjects | AOD-9604 |
Human weight loss | ~1.8 kg over placebo; programme discontinued 2007 | AOD-9604 |
Tyrosine substitution for stability | Real — it is what defines AOD-9604 | AOD-9604 |
β-adrenergic mechanism | Explicitly ruled out by the original researchers | Neither |
Waist-circumference and body-composition results in humans | No source exists | Neither |
Spot reduction via localised injection | No study in either compound's literature | Neither |
The native fragment is glucose-neutral | 1978 and 1982 papers report hyperglycaemic action | Contradicted |
Read down the verdict column and the shape of the problem is obvious: not one row resolves to HGH Fragment 176-191.
Is HGH Fragment 176-191 approved or legal to use?
Neither compound is approved for human use by the FDA, the EMA or the TGA. On US compounding, AOD-9604 was placed in 503A Category 2 in September 2023, and at the Pharmacy Compounding Advisory Committee meeting of December 4, 2024 the committee voted against adding AOD-9604 free base and acetate to the 503A bulks list — 0 in favour, 12 against, 0 abstentions. Both are prohibited at all times under WADA S2.2.3.
That unanimity is worth noting. The same committee structure that in July 2026 narrowly advanced BPC-157, TB-500, KPV and MOTS-c had, eighteen months earlier, rejected AOD-9604 without a single supporting vote. AOD-9604 was not on the July 2026 agenda and no re-review is pending. The unmodified fragment has never been separately nominated, which means it has not been rejected either — it has simply never been considered.
The WADA entry names both explicitly: S2.2.3 covers "growth hormone fragments, e.g. AOD-9604 and hGH 176-191", as non-specified substances on the 2026 Prohibited List. The TGA position is unapproved for human use, and the wider picture is in our FDA peptide regulation timeline.
What dose is used, and which two practices should be retired?
No human study has ever dosed the unmodified fragment, so no validated protocol exists. Community convention runs to 250–500 mcg per day subcutaneously, extrapolated from AOD-9604 material and from rodent dosing that used a different molecule at mg/kg scale. Two practices should be retired: localised injection for spot reduction, which neither programme tested, and subcutaneous administration itself — the AOD-9604 trials that produced the human record were oral.
Localised injection for spot reduction. The idea that injecting into the abdomen or thighs produces fat loss specifically there has no support in either compound's literature. Neither programme tested it, so there is no result to be sceptical of — there is nothing.
Subcutaneous administration as the assumed route. The entire human record for this compound class was generated orally. The gray market administers it by injection, which is the opposite of how the evidence was produced. Treat any protocol that cites AOD-9604's human data while specifying subcutaneous dosing as internally inconsistent. For reconstitution arithmetic on whatever is actually in the vial, use the peptide dosing calculator alongside the reconstitution calculator.
How do you tell which molecule is in the vial?
Mass spectrometry, and only mass spectrometry. HGH Fragment 176-191 returns 1,799 Da; AOD-9604 returns 1,815 Da. That 16-dalton gap is the entire identity test, because a vial can be 99% pure and still contain the other compound — HPLC purity measures how much of a single species is present, not which species. The CAS numbers differ too: 66004-57-7 for the fragment, 221231-10-3 for AOD-9604. Many vendors do not distinguish the two either.
Check | What it confirms | How | Red flag |
|---|---|---|---|
Mass spectrometry | Which molecule you have — 1,799 Da (fragment) vs 1,815 Da (AOD-9604) | Batch-matched CoA with MS | Only HPLC purity reported |
CAS on the label | Vendor knows which one it sells | 66004-57-7 vs 221231-10-3 | A CAS matching neither, or none given |
HPLC purity | Proportion of intended peptide | Third-party CoA, named lab | Vendor's own document only |
Net peptide content | Peptide versus salts and water | Net content or amino acid analysis | Purity quoted as if it were quantity |
Marketing consistency | Whether the vendor understands its own product | Does it cite AOD-9604 trials while selling "Fragment"? | Mixed citations for mixed products |
Peptigrity's own data audit demonstrated the problem at scale: AOD-9604 products were being filed under the fragment's entity because no separate compound page existed, contaminating both compounds' purity statistics until the entities were split. That is the conflation operating inside a database built by people paying attention, and it is why the AOD-9604 compound page now exists separately.
See mass spectrometry for peptides and how to read peptide lab test results. Peptigrity tracks 530 shops and 11,852 independent lab tests across 118 peptides, with 1,283 community reviews (verified August 2026). Trust scores weight community reviews and independently verified HPLC purity equally, at 50% each, with no financial relationship influencing the ranking. Per-compound purity and test counts are read live from the Purity Index, independent results from the lab test database, and per-milligram offers with shops-in-stock, median and lowest price from HGH Fragment price data. Those figures exclude shipping, taxes and customs, coupon codes, bulk tiers, multi-vial kits and account-gated pricing.
Compound | Mechanism | Human evidence | Status |
|---|---|---|---|
HGH Fragment 176-191 | GH lipolytic domain (proposed) | None | Unapproved; WADA S2.2.3 |
AOD-9604 | GH lipolytic domain | 6 trials, ~893 subjects; discontinued 2007 for insufficient efficacy | Unapproved; PCAC rejected 0–12 |
Tesamorelin | GHRH analogue | Phase 3 in HIV lipodystrophy | FDA-approved (Egrifta) |
Semaglutide | GLP-1 agonist | Large Phase 3 programme | FDA-approved |
The comparison that matters most is with tesamorelin: a GH-axis compound targeting visceral fat that went through proper trials and earned an approval. It is what success looks like in this category, and it shows the bar AOD-9604 failed to clear. For appetite-mediated alternatives, see semaglutide science and cagrilintide science.
What is still unknown, and what trial would settle it?
Everything about the unmodified fragment in humans is unknown: no human study has dosed it, no body-composition or waist-circumference result exists for it, and its only original literature reports a hyperglycaemic action rather than glucose neutrality. The trial that would settle it is a head-to-head comparison of the two molecules in the same protocol. None is planned — AOD-9604 was not on the July 2026 committee agenda, and the fragment has never been separately nominated.
The trial that would settle this.
Element | What it would have to be |
|---|---|
Question | Does the unmodified fragment do anything AOD-9604 does — and does it raise blood glucose? |
Design | Randomised, double-blind, placebo-controlled, all three arms inside one protocol |
Arms | HGH Fragment 176-191 vs AOD-9604 vs placebo |
Population | Adults with obesity, glucose tolerance measured at baseline |
Route | Both oral and subcutaneous — the human record is oral, the market injects |
Co-primary endpoints | Fat mass by DXA, and fasting and post-load glucose |
Identity control | Every batch confirmed by mass spectrometry, 1,799 vs 1,815 Da, before dosing |
Why it hasn't run | AOD-9604 was discontinued in 2007 and rejected 0–12 by the PCAC; the fragment has never been separately nominated |
Until such a study exists, treat every number attached to HGH Fragment 176-191 as AOD-9604's until proven otherwise. Check the mass first if a vendor cites trial data, because the citation and the vial may not describe the same molecule.
Frequently Asked Questions
Is HGH Fragment 176-191 the same as AOD-9604?
No. AOD-9604 is the 177–191 sequence with an added N-terminal tyrosine — 16 Da heavier, with its own CAS number and its own clinical record. Citations for one are not valid for the other.
Does it raise blood sugar?
For AOD-9604, human trials found no glucose effect. For the unmodified fragment there is no human data, and the only original research on C-terminal hGH fragments describes a hyperglycaemic action. The confident "no glucose impact" claim comes from the other molecule.
Is it better than growth hormone for fat loss?
AOD-9604 was designed to test that proposition and produced about 1.8 kg more weight loss than placebo before being discontinued for insufficient efficacy. That is not the conclusion the trial programme reached.
Does injecting into a fat area target fat there?
No study in either compound's literature tested localised injection for localised fat loss. There is no positive finding to weigh and no negative finding either — the question was never put.
Why do so many sources get this wrong?
Older papers sometimes wrote "HGH Fragment 176-191" when they meant AOD-9604, and commercial descriptions inherited the conflation. It has since been repeated so widely that the fragment's marketing consists almost entirely of another molecule's résumé.
How do I know which one I bought?
Mass spectrometry: 1,799 Da is the fragment, 1,815 Da is AOD-9604. Nothing else distinguishes them reliably, and a purity certificate will look identical for both.
There are two honest stories here, and neither supports the marketing. AOD-9604 is a real drug candidate that was properly developed, properly tested in nearly 900 people, and properly abandoned when the efficacy did not justify it. An advisory committee later rejected it 12–0.
HGH Fragment 176-191 is a molecule with no human research whose entire reputation is borrowed from that failed programme — and whose own small literature reports the opposite of its central selling point.
Browse the weight loss and metabolic peptides category, or our complete peptide guide with 118 compounds (verified August 2026). For reconstitution and per-injection volume, use the peptide dosing calculator alongside the reconstitution calculator. Compare shops through independent lab tests and community-verified shop reviews.
This article is for educational and informational purposes only and does not constitute medical advice. Peptides discussed may be investigational compounds not approved by the FDA (or equivalent regulators in your jurisdiction) for human use. Always consult a qualified healthcare provider before using any peptide or research compound. Peptigrity is an independent review platform and does not sell, endorse, or recommend specific products or vendors.
