What Is AOD-9604?

Published August 2026 · Patriot Labs Research Team · ~15 min read

Growth hormone, minus the growth

Human growth hormone is a single protein of 191 amino acids that does many jobs at once. It promotes the growth of bone and soft tissue, largely through the messenger IGF-1; it influences how the body handles glucose; and, separately from both of those, it acts on fat, encouraging its breakdown. For a drug developer those overlapping activities are a problem. Anyone who wanted the fat-metabolizing action of growth hormone had to accept the growth-promoting and glucose-disturbing actions along with it. The premise behind AOD-9604 was that the activities might be separable — that a small piece of the hormone might carry the effect on fat and leave the rest behind.

AOD-9604 — the letters stand for “Anti-Obesity Drug,” the program name it was given, though as this guide will show that name promised more than the molecule delivered — is that small piece, with one modification. It is a synthetic fragment corresponding to the last stretch of the growth-hormone chain, the region long identified as the hormone’s lipolytic domain (lipolysis being the breakdown of stored fat). In cell and animal studies that fragment reproduced the lipid-metabolism activity of the whole hormone; in the same studies it did not meaningfully raise IGF-1 or blood glucose. Whether that clean separation translated into a useful clinical result is the harder question, and the honest answer is a qualified one that the rest of this guide builds toward. To place the molecule in the wider family, the site’s overview of what peptides are is the natural starting point, and its comparison of AOD-9604 against the GLP-1 class sets it beside the compounds it is most often measured against.

The chemistry: sixteen residues and a disulfide loop

AOD-9604 is a hexadecapeptide — sixteen amino acids — and in one-letter code the sequence is YLRIVQCRSVEGSCGF.¹ Fifteen of those residues are taken directly from the C-terminal region of human growth hormone; the sixteenth, the tyrosine (Y) at the very front, is not part of the natural hormone at all. It was added deliberately, and the reason it was added is the first thing worth understanding about the molecule.

The peptide carries the molecular formula C₇₈H₁₂₃N₂₃O₂₃S₂, an average molecular weight of roughly 1815 g/mol, and the CAS registry number 221231-10-3.¹ For scale, that is a small fraction of the mass of intact growth hormone, which is around 22,000 g/mol. The two sulphur atoms in the formula are the giveaway for the structural detail that matters most: the sequence contains two cysteine residues, and in the correctly folded molecule they are joined by an intramolecular disulfide bond. That bond pins the chain into a small loop, recreating the disulfide-bonded loop that exists at the C-terminus of the parent hormone. It is not incidental. The loop is part of the shape the molecule presents, and — as the handling section returns to — a vial in which that bond has been reduced or scrambled no longer contains the same structure, even if the amino-acid content on paper is unchanged.

The rest of the sequence is unremarkable in the useful sense: a short, mostly polar chain with a couple of basic arginines and no exotic modifications beyond the added tyrosine and the disulfide. That is exactly why it can be made reliably by standard solid-phase peptide synthesis, and why its identity and purity are straightforward to verify with routine analytical tools. Short, defined, and synthesizable is the combination that makes a peptide practical for laboratory work.

AOD-9604 versus “hGH fragment 176–191”

Search for this molecule and two labels come back interchangeably: AOD-9604 and hGH fragment 176–191 (often shortened to “HGH Frag”). They are related, they are frequently confused, and they are not the same thing — a distinction a research audience should be able to state precisely.

The numbers 176–191 refer to positions in the 191-residue growth-hormone chain; that stretch is the natural fragment long associated with the hormone’s effect on fat. AOD-9604 is a modified version of that region. The two differences are the ones already noted: the developers worked from the residues numbered 177–191 and added a tyrosine to the N-terminus, producing the sixteen-residue chain above. That added tyrosine is the whole point of the modification — it was introduced to improve the peptide’s stability relative to the unmodified fragment. So “hGH fragment 176–191” is a loose, popular name that AOD-9604 has inherited, and it is close enough that catalogues and articles use the terms as synonyms, but the accurate description is that AOD-9604 is a tyrosine-stabilized analogue of the growth-hormone C-terminal fragment rather than the unmodified fragment itself. The looseness of the “176 versus 177” numbering in the literature is a minor historical artefact; the tyrosine is the substantive change.

From a hormone’s side activity to a drug candidate

The scientific groundwork was laid in Australia. Researchers at Monash University, in a line of work associated with the biochemist F. M. Ng and colleagues, characterized the lipolytic activity residing in the C-terminal region of growth hormone and pursued the idea that this activity could be captured in a short synthetic peptide. That research was developed commercially by Metabolic Pharmaceuticals Ltd, an Australian company (later connected to the listed entity Calzada Ltd), which took AOD-9604 forward as a drug candidate for obesity.²

The logic of the program was the separation described above, now stated as a development thesis: full growth hormone was already known to act on fat, but its growth-promoting and glucose-related activities made it unattractive as a weight-management drug. If a fragment could reproduce only the lipid effect, it might sidestep those liabilities. Through the late 1990s and 2000s the company assembled the preclinical case — cell studies and rodent models — and then moved into human trials. The trials were catalogued under program codes that still appear in the literature: intravenous studies designated METAOD001 and METAOD002, and oral studies designated METAOD003 through METAOD006, reflecting an effort to develop the peptide in an orally dosed form as well as an injectable one.³ This is worth pausing on, because a peptide that could be taken by mouth would have been a notable achievement in itself; most peptides are digested before they can act, which is part of why the field relies so heavily on injection, a constraint the site’s peptide-versus-drug explainer unpacks.

The mechanism the studies pointed to

What AOD-9604 was studied to do, and how, comes mainly from preclinical work. In adipocyte (fat-cell) and rodent models the fragment was reported to stimulate lipolysis — the breakdown of stored triglyceride — and to inhibit lipogenesis, the laying-down of new fat. Those two directions together are what earned it the “fat-metabolism” description. Crucially, the same body of work reported that it did this without the somatotropic (growth-promoting) signalling of intact growth hormone, and without significantly raising IGF-1 or blood glucose.² That negative result — the things it did not do — is as much a part of its research identity as the lipolysis itself.

The most-cited mechanistic study is a 2001 paper in Endocrinology by Heffernan and colleagues from the Monash group, which examined the effects of growth hormone and of AOD-9604 on lipid metabolism after chronic treatment in obese mice and in mice genetically lacking the β3-adrenergic receptor (a receptor on fat cells involved in fat breakdown).² The result that made the paper a reference point: in the animals missing the β3-adrenergic receptor, the lipid effect was lost. That pointed to the β3-adrenergic pathway as central to how the fragment acts in these models, and later work has described associated changes such as increased expression of the β3-adrenergic receptor and effects on the enzyme machinery of fat storage. Even so, an honest account has to note the gap: the precise molecular target through which AOD-9604 initiates its effect — the receptor it binds first, if any single one — has never been fully pinned down in the published literature. It is a peptide whose downstream signature is better characterized than its first point of contact.

For readers placing this beside other growth-hormone-axis compounds the catalogue carries, the contrast is instructive. Secretagogues such as CJC-1295, ipamorelin, and tesamorelin work by prompting the body’s own release of growth hormone — and therefore raise IGF-1 as part of their studied action. AOD-9604 sits at the opposite end of the same axis: a fragment designed to avoid the IGF-1 arm entirely. Two research strategies aimed through the same hormone in different directions.

The clinical record: what the obesity trials showed

Here is where the story turns, and where a careful guide has to resist the marketing gravity that surrounds this molecule. AOD-9604 was not merely a bench curiosity; it went into human beings, in company-run clinical trials, with obesity as the target. That is more clinical development than many research peptides ever see. The problem is how the trials came out.

The compound advanced to Phase IIb, the stage at which a candidate is tested in a larger patient group to establish whether it produces a real, dose-related effect. In that trial AOD-9604 did not meet its primary efficacy endpoint — the pre-specified measure of weight reduction it needed to hit to justify moving forward. Development of the peptide as an obesity drug was discontinued in the second half of the 2000s, around 2007.³ Earlier and smaller studies had generated more encouraging signals, which is part of why the compound retains a following, but the larger, more rigorous test is the one that counts, and it was not passed. This is the single most important fact to hold onto when reading any enthusiastic description of AOD-9604: the definitive obesity trial was negative.

What the human program did establish is a safety and tolerability record, and that record was later summarized in the peer-reviewed literature. A 2013 paper in the Journal of Endocrinology and Metabolism by Stier and colleagues, titled “Safety and Tolerability of the Hexadecapeptide AOD9604 in Humans,” drew together data from the clinical studies and reported that the peptide was well tolerated across the doses tested, with no significant effect on IGF-1 or on glucose handling — consistent with the separation the molecule was designed around.⁴ So the human data tell a two-part story that is easy to garble: the fragment behaved in people much as its design predicted at the level of hormones and safety, and it nonetheless failed to demonstrate the weight-loss efficacy that would have made it a drug.

Beyond obesity: cartilage, cosmetics, and GRAS

A failed primary indication does not always end a molecule’s life, and AOD-9604 is a good example of a compound that found other roads after its main one closed. Three are worth noting, because they explain why the peptide remained in circulation and in the literature long after the obesity program stopped.

The first is a pivot toward cartilage and joint research. Once the systemic weight-loss route was abandoned, investigators examined whether the peptide had a role in local tissue repair. A representative study is Kwon, Park and Lee (2015) in Annals of Clinical & Laboratory Science, which looked at intra-articular injection of AOD9604, with and without hyaluronic acid, in a rabbit model of osteoarthritis.⁵ Work of this kind is preclinical and exploratory, and it should be read as such — an animal-model investigation of a possible tissue effect, not a demonstration of a treatment. But it marks a genuine second research direction distinct from the metabolic one.

The second is a move into food-ingredient and cosmetic regulation. Rather than pursue the difficult and expensive drug pathway, Metabolic Pharmaceuticals sought non-drug status for the peptide, and AOD-9604 was the subject of a GRAS (“generally recognized as safe”) determination for use as a food or beverage ingredient in the mid-2010s, as well as being used as a cosmetic ingredient.⁴ The distinction here matters and is easy to blur: a GRAS determination for a food-additive use is a regulatory category entirely separate from approval as a therapeutic drug, and it is separate again from the sale of the compound as a research chemical. Three different regulatory worlds, one molecule.

The through-line of these later chapters is that AOD-9604 is a well-travelled compound with a long paper trail, which is precisely what makes it a useful subject for a research programme: its chemistry is settled, its behaviour in several models is documented, and its history is unusually well recorded for a peptide of its class.

Regulatory status and anti-doping

Because AOD-9604 is discussed in so many different registers — failed drug, food ingredient, research chemical, sports-supplement controversy — its regulatory status is genuinely tangled, and it is worth laying out plainly. As a therapeutic drug it is not approved by the FDA for any indication; no marketing application was completed. In the anti-doping world it is treated as prohibited under the World Anti-Doping Agency framework, both as a non-approved substance and by virtue of its growth-hormone-related biology; laboratories and athletes operating under those rules should treat it as banned. Its anti-doping status became a matter of public record during the 2012–2013 investigation into supplement use at Australia’s Essendon Football Club, a saga in which the ambiguous classification of AOD-9604 was itself a point of contention.

The compound has also re-entered the regulatory conversation more recently. Peptides sold and used outside the approved-drug system have drawn increasing attention from the FDA, including a 2024–2026 review process examining which peptide substances should or should not be available through compounding, and AOD-9604 is among the many compounds named in that broader docket.⁶ None of that changes the footing on which a research supplier operates: whatever a compound’s regulatory trajectory, research-grade AOD-9604 is laboratory material, sold for in-vitro research use only, and the current attention on the category is a reason to be more precise about that framing, not less. The site’s guide to how peptides differ from drugs and biologics covers why these categories are drawn where they are.

Bench practice: characterizing a disulfide peptide

AOD-9604 is supplied as a lyophilised (freeze-dried) solid, and the analytical questions a laboratory should be able to answer about a vial follow directly from the chemistry. Two properties define the target: the correct sixteen-residue sequence, and the correct disulfide bond linking its two cysteines. A credible certificate of analysis should let a buyer confirm both.

Identity is established by mass spectrometry: the measured mass should match the expected value for the peptide (an average near 1815). Purity is established by reversed-phase HPLC, which separates the intended molecule from synthesis-related impurities such as deletion sequences and, importantly for this peptide, from forms in which the disulfide bond is missing (reduced) or mis-paired (scrambled). Because the disulfide loop is part of what defines the correct structure, disulfide integrity is a specific quality concern here in a way it is not for a simple linear peptide — two vials with identical amino-acid content can still differ if one has a properly formed bond and the other does not. Beyond identity and purity, a thorough COA reports net peptide content (how much of the vial’s mass is actually peptide rather than water and counter-ions), the counter-ion itself (commonly acetate or trifluoroacetate), and endotoxin levels for work where that matters.

Stability follows the general rules for the class rather than anything unique. As a dry, lyophilised solid stored cold and protected from light and moisture, the peptide is comparatively stable; once reconstituted it is far more vulnerable, and a disulfide-bonded molecule has the added consideration that reducing conditions can break the bond that holds its loop together. The site’s storage guide and its account of how peptides degrade cover the practical handling; none of that is a use instruction, only the analytical hygiene that lets a laboratory trust that what is in the vial matches the label.

What the evidence does not establish

AOD-9604 attracts more claims than its evidence supports, and the corrective is to state the boundaries directly. The defining clinical fact is negative: the Phase IIb obesity trial did not meet its primary endpoint, and the compound was not approved as a drug. The mechanistic and preclinical work — the lipolysis, the β3-adrenergic dependence, the sparing of IGF-1 and glucose — is real and peer-reviewed, but it describes what the fragment does in cells and animals and in short human studies of hormones and safety. It does not amount to a demonstrated weight-management effect in people, and it says nothing about outcomes for any individual.

The popular framing of AOD-9604 as a “fat-loss peptide” is exactly the kind of shorthand a research audience should hold at arm’s length: it collapses a nuanced record — promising early signals, a negative pivotal trial, a well-documented safety profile, and a pivot to entirely different uses — into a slogan the definitive trial did not earn. For placing the compound against the drug classes that did reach approval for metabolic indications, the comparisons with the GLP-1 class and with retatrutide are the honest reference points, and the broader survey of metabolism-related research peptides puts the whole category in context.

The honest summary is that AOD-9604 is a thoroughly characterized, well-travelled research peptide with a clear chemistry, an instructive mechanism, and a clinical history whose main lesson is caution. That combination is exactly what makes it a legitimate subject for laboratory investigation — and it is exactly why it belongs in a research setting and nowhere else.

Frequently asked questions

Is AOD-9604 the same as hGH fragment 176–191?

They are closely related but not identical. Both are short peptides taken from the C-terminal, fat-metabolizing region of human growth hormone. AOD-9604 is a modified version: it carries an extra tyrosine residue added to the front of the chain, a change its developers introduced to improve the molecule’s stability. So AOD-9604 is best described as a tyrosine-stabilized analogue of the growth-hormone C-terminal fragment that is loosely labelled 176–191 in the popular literature, rather than that unmodified fragment itself.

Why was AOD-9604 designed to leave IGF-1 and blood glucose alone?

Full-length human growth hormone does several things at once: it drives tissue growth through IGF-1, it can raise blood glucose, and it also acts on fat metabolism. The research idea behind AOD-9604 was to isolate only the last of those activities. In the published preclinical and clinical work the fragment was characterized as acting on lipid metabolism without significantly raising IGF-1 or blood glucose, which is the property that distinguished it from the parent hormone in the models studied. This is a description of research findings, not a benefit offered to any reader.

Did AOD-9604 succeed as an obesity drug in clinical trials?

No. AOD-9604 was taken through human trials for obesity by Metabolic Pharmaceuticals in the 2000s, but a Phase IIb study did not meet its primary efficacy endpoint, and development of the compound as an obesity drug was discontinued around 2007. It has never been approved by the FDA as a drug for any indication. That commercial outcome is an important part of reading the molecule honestly.

Is AOD-9604 banned in sport?

Yes. AOD-9604 is treated as prohibited under the World Anti-Doping Agency framework, both because it is a non-approved substance and because of its relationship to growth-hormone biology. Its status drew public attention during the 2012–2013 Australian sports-supplement investigation involving the Essendon Football Club. Any organization operating under anti-doping rules should treat it accordingly.

Is AOD-9604 approved for human use?

No. There is no approved AOD-9604 drug product. It reached a food-ingredient regulatory determination and has been used in cosmetics, but as a research chemical it is a different thing entirely. AOD-9604 supplied by Patriot Labs is sold strictly for in-vitro research and laboratory use only, is not for human or veterinary consumption, and nothing in this guide describes how to use it. For the practical side of sourcing verified material, see the guide on storing research peptides and the COA explainer.

References

All Patriot Labs products are sold strictly for in-vitro research and laboratory use only. Not for human or veterinary consumption. This guide is educational and describes peptide chemistry and published research in general terms; it is not medical advice, does not describe how to use any product, and the references cited do not constitute a product claim.