# AOD-9604: The Tyrosine-Extended Growth Hormone Fragment in Metabolic Research > A 16-residue C-terminal hGH fragment built to separate fat metabolism from the IGF-1 axis, and an honest look at what the evidence does and does not show. Web page: https://peptidemedixeu.com/en/learn/what-is-aod-9604/ · Peptide Medix EU · 6 min read · Updated: 2026-04-17 AOD-9604 is a 16-amino-acid synthetic peptide taken from the tail end of human growth hormone, residues 176 to 191, with one additional tyrosine placed at the N-terminus. The design rested on a hypothesis: that growth hormone's action on fat could be uncoupled from its growth-promoting and glucose-related effects. This fragment covers the stretch that published work links to fat metabolism while missing the binding surfaces required to drive the IGF-1 axis. Our [research-grade AOD-9604](https://peptidemedixeu.com/en/products/aod-9604/) ships as lyophilized powder in sealed vials, for laboratory use only. ## A precise definition The full hormone runs to 191 residues. From the 1990s onwards, papers reported that its adipose-tissue effects could be recreated using only a short C-terminal stretch, and that this stretch worked without the whole hormone and without the receptor dimerisation that generates IGF-1. AOD-9604, whose name abbreviates "anti-obesity drug", is the engineered form of that stretch: hGH(177-191) plus an N-terminal tyrosine, 16 residues in all. That extra tyrosine makes the peptide easier to synthesise and supplies a UV chromophore, a real analytical benefit because the molecule then absorbs at 280 nm. The native fragment's two cysteines remain joined by a disulfide bridge, closing the small loop on which the reported activity depends. This is a genuine fragment peptide rather than an analogue of the intact hormone, and functionally it is not growth hormone at all. ## Origin and structure - Source sequence. The C-terminal segment of human growth hormone, residues 177-191. - Added residue. A tyrosine at the N-terminus, which is what separates AOD-9604 from plain HGH Fragment 176-191. - Disulfide loop. An internal Cys-Cys bond creating the ring the reported activity requires, shown by the two sulfur atoms in the formula. - Identifiers. CAS 221231-10-3, formula C78H123N23O23S2, mass 1815.08 Da. Around 1.8 kDa makes this a small molecule by metabolic-peptide standards, with three practical results: it goes into aqueous buffer without difficulty, it tolerates handling better than a bulky acylated peptide, and it is eliminated fast, because nothing binds it to albumin and nothing slows glomerular filtration. ## Proposed mechanism The mechanism is considerably less certain than promotional copy about this peptide implies, and a research page ought to say as much. Preclinical publications describe the fragment promoting lipolysis and suppressing lipogenesis in fat tissue, with data from isolated adipocytes and from rodent [obesity](https://peptidemedixeu.com/en/learn/research-catalog-obesity/) models. Beta-3 adrenergic signalling in adipose tissue features in several papers, but the connection is characterised as permissive or indirect rather than as direct agonism, and beta-3 knockout experiments muddied the picture instead of settling it. Better supported is the negative property the molecule was engineered for: in contrast to intact growth hormone, AOD-9604 has not been reported to elevate IGF-1 or to produce the growth effects that follow growth hormone receptor activation. That separation is the genuinely interesting feature of the compound and the reason it shows up in adipose research as a probe of lipolytic signalling independent of growth hormone. ## Research to date - Adipocyte work. Isolated adipocyte and cell culture experiments tracking glycerol and free fatty acid output, lipogenic enzyme activity and lipolytic signalling. This forms the backbone of the evidence. - Rodent work. Adiposity and body composition in obese mice and rats, with the absence of IGF-1 elevation reported repeatedly as an endpoint. - Clinical trials. Early-phase studies were run, and the published outcomes failed to show the weight effects the preclinical data had implied. This part of the story is regularly left out, yet the gap between rodent adipocyte findings and human results is exactly why the compound never reached approval. - Joint and cartilage studies. A smaller preclinical literature has tested the fragment in cartilage and osteoarthritis models, quite separate from its metabolic origins. Our article on the growth hormone lipolytic fragment gives a fuller account of the two fragments and what distinguishes them. Reading this literature properly means keeping two propositions apart. One is biological: that a short C-terminal region of growth hormone carries lipolytic information, a claim with genuine in vitro backing. The other is therapeutic: that this produces meaningful change in an intact organism, which human trials did not support. Preclinical papers often cite the first as if it settled the second. Using this peptide as a probe of adipocyte signalling is defensible; treating it as a validated metabolic intervention is not. ## Formats and sizes Vials for injection are listed on the AOD-9604 product page, and a sublingual presentation appears as [AOD-9604 troches](https://peptidemedixeu.com/en/products/aod-9604-troches/). Both belong to the fat-loss and metabolic peptides collection. Format carries more weight for a small unmodified peptide than for the acylated [incretins](https://peptidemedixeu.com/en/glossary/incretin/). Something of 1.8 kDa with no albumin-binding chain clears quickly and crosses mucosal surfaces poorly, so [sublingual](https://peptidemedixeu.com/en/glossary/sublingual-troche/) and oral versions of this molecule are better regarded as delivery experiments than as substitutes for a reconstituted vial. Where a design depends on knowing how much compound is present, only the injectable lyophilized format allows that quantity to be derived from first principles. Our note on oral and sublingual peptide formats explains why bioavailability sets the limit. ## Reconstitution and storage in the lab The calculation is simple: 5 mg reconstituted in 2 mL of bacteriostatic water produces 2.5 mg/mL, that is 2,500 mcg/mL, so 0.1 mL of the solution carries 250 mcg of peptide. Small unmodified peptides of this kind [go into solution](https://peptidemedixeu.com/en/learn/ph-and-solubility-of-peptides/) readily and survive handling better than acylated analogues, but the disulfide bridge is a genuine vulnerability: reducing environments, long spells in alkaline buffer and stray thiols in an ill-chosen diluent can each break the loop open. Keep sealed lyophilized powder at minus 20 degrees Celsius, away from light and moisture, and hold reconstituted solution at 2 to 8 degrees Celsius for use within the study period. Split it into aliquots at reconstitution to avoid [repeated freezing and thawing](https://peptidemedixeu.com/en/glossary/freeze-thaw-cycle/). See our reconstitution guide. ## Purity and reading the COA Expect a certificate carrying an HPLC chromatogram with main-peak area percentage, mass spectrometry identity against the theoretical 1815.08 Da, net peptide content, lot number and date of analysis. Two checks matter especially. The disulfide state comes first: an open-loop form differs by just two mass units, which a low-resolution spectrum will miss, yet pharmacologically it is another molecule. The second is discrimination from the unmodified fragment, since AOD-9604 and [HGH Fragment 176-191](https://peptidemedixeu.com/en/learn/what-is-hgh-fragment-176-191/) sit about two daltons apart in our catalogue figures, so a substitution of one for the other would slip past a purity percentage unnoticed. Insist on a mass result with sufficient resolution; see mass spectrometry identity. One further practical point concerns detection. Thanks to the added tyrosine, AOD-9604 absorbs measurably at 280 nm, which the unmodified fragment essentially does not, so a laboratory quantifying the peptide by UV can use a wavelength with far less interference than the 214 nm peptide-bond band. Buffers, solvents and plasticware all absorb strongly around 214 nm, and almost nothing absorbs at 280 nm. Wherever recovered peptide has to be measured rather than assumed, as in stability testing, uptake experiments or any assay dependent on actual concentration, that single residue is a considerable methodological gain. ## Regulatory position AOD-9604 is not an authorised medicine in the European Union, the United States or anywhere else. It has been assessed as a food ingredient in certain jurisdictions, a fact sometimes presented as therapeutic approval, which it is not. Research-grade AOD-9604 is supplied as a laboratory reference chemical, and the compound also features on sports anti-doping prohibited lists. ## Related compounds and comparisons The natural comparison is AOD-9604 vs HGH Fragment 176-191, its unmodified parent. Laboratories studying metabolic signalling independent of growth hormone frequently look at 5-Amino-1MQ as well. ## Frequently asked questions ### What is the meaning of the name AOD-9604? It abbreviates "anti-obesity drug 9604", the development code used by the programme that created it. The label records the original research aim rather than any demonstrated property, and it should not be taken as a statement about activity in people. ### What separates AOD-9604 from HGH Fragment 176-191? One residue. AOD-9604 is hGH(177-191) with a tyrosine added at the N-terminus, making 16 residues, whereas the unmodified fragment is hGH(176-191). The tyrosine eases synthesis and introduces a UV chromophore at 280 nm, which simplifies analytical detection. ### Does AOD-9604 increase IGF-1 as growth hormone does? Preclinical reports say it does not. The fragment lacks the surfaces needed for growth hormone receptor dimerisation and the IGF-1 response that follows, which is exactly the separation the molecule was built to achieve and why it serves as a probe of lipolytic signalling independent of growth hormone. ### What came out of the human trials? Early-phase clinical studies were completed, and their published results did not reproduce the weight changes seen in rodent and adipocyte experiments. That failure to translate is the principal reason the compound never gained approval, and it is a material part of the evidence that promotional descriptions tend to omit. ### Is the mechanism settled? It is not. Preclinical data describe increased lipolysis and reduced lipogenesis in fat tissue, with beta-3 adrenergic signalling implicated only indirectly, and knockout work has complicated rather than confirmed that link. The mechanism should be presented as proposed and unresolved, not as established pharmacology. ### What should an AOD-9604 certificate confirm? Main-peak area by HPLC, net peptide content, lot number, analysis date and a mass spectrometry identity result resolved well enough to confirm both the correct mass and an intact disulfide bridge. The open-loop form is only two mass units away, and the unmodified 176-191 fragment is close in mass too. ### Is AOD-9604 approved anywhere? No jurisdiction has authorised it as a medicine. Its review as a food ingredient in some countries is occasionally portrayed as therapeutic approval, which it is not. Research-grade material is sold as a laboratory reference chemical, and the peptide is listed by anti-doping authorities as prohibited. ## Related products - [AOD-9604](https://peptidemedixeu.com/en/products/aod-9604/): from €63 --- For laboratory research use only. This page is provided for scientific and educational information. Materials referenced here are sold strictly for in-vitro laboratory research by qualified professionals — not for human or veterinary use, and nothing on this page is medical advice.