AOD9604 is a synthetic 16-amino-acid peptide corresponding to residues 177–191 of the C-terminal region of human growth hormone (hGH) with an N-terminal tyrosine added — written Tyr-hGH(177–191). In laboratory research it is studied as a tool for investigating lipid metabolism and lipolytic signaling in adipocyte and animal models, and it is of interest because published studies report that it retains hGH's lipolytic-associated activity in these systems without binding the growth hormone receptor or measurably raising insulin-like growth factor 1 (IGF-1). This compound is supplied strictly for in-vitro and laboratory research use only, and is not for human or animal consumption.
Research Background
AOD9604 (sometimes written AOD-9604 or referred to as "hGH fragment 176–191") emerged from work at Monash University in Australia in the 1990s and early 2000s that sought to isolate the specific region of human growth hormone responsible for its effects on fat metabolism. Full-length hGH influences both growth-related pathways and lipid metabolism, and researchers were interested in whether a short C-terminal fragment could reproduce the lipolytic-associated signaling seen in laboratory systems while separating it from the receptor-mediated growth and glucose effects of the intact hormone. AOD9604 is the fragment that came out of that line of investigation, and it has since been used as a model compound in metabolic, adipose-tissue, and — more recently — cartilage research.
As of 2026, AOD9604 remains an actively referenced compound in the peptide research literature, and it continues to appear in laboratory studies and reviews concerned with adipocyte signaling, lipolysis assays, and mitochondrial and connective-tissue models. Its relatively well-characterized safety and pharmacokinetic profile in preclinical testing is one reason it is frequently chosen as a research tool.
Structure and Chemistry
AOD9604 is a 16-amino-acid peptide comprising hGH residues 177–191 with a tyrosine added at the N-terminus (Tyr-hGH 177–191). Because position 176 of native hGH is a phenylalanine, the same molecule is sometimes described equivalently as the 176–191 fragment with the N-terminal residue changed to tyrosine — hence the common informal name "hGH fragment 176–191." Because it corresponds to the lipolytic domain of hGH rather than the whole protein, it is a small, defined peptide rather than a full-length hormone. This is central to how it is studied: researchers use it to probe which downstream pathways are engaged by the C-terminal domain in isolation, independent of the somatogenic (growth-promoting) and receptor-binding activity associated with intact hGH.
Mechanism of Action (Studied Pathways)
The mechanisms of AOD9604 are still being characterized, but several themes recur across the published literature. A major focus is its relationship to the beta-3 adrenergic receptor (β3-AR) pathway, the dominant lipolytic receptor system in fat cells. In a 2001 study in Endocrinology, both hGH and AOD9604 increased the expression of β3-AR messenger RNA in obese mice and raised the repressed β3-AR levels toward those seen in lean animals. Notably, in β3-AR knock-out mice, chronic treatment failed to reproduce the changes in body weight and lipolysis observed in wild-type controls, indicating that β3-AR expression contributes to the lipolytic sensitivity seen in these models — although the authors concluded the acute lipolytic actions were not mediated directly through the β3-AR itself.
At the cellular level, the C-terminal hGH domain has been associated in laboratory work with stimulation of hormone-sensitive lipase (HSL) and inhibition of acetyl-CoA carboxylase, enzymes involved in triglyceride breakdown and fatty-acid synthesis respectively. A frequently cited distinguishing feature is that, in the reported studies, AOD9604 did not compete for the hGH receptor and did not elevate IGF-1, which separates its studied metabolic effects from the growth-signaling arm of the full hormone.
Published Research Overview
Metabolic and lipolysis studies
One of the foundational reports, published in Hormone Research in 2000 by Ng and colleagues, examined AOD9604 in obese Zucker rats. In that study, an oral dose of 500 µg/kg body weight administered daily for 19 days reduced body-weight gain by more than 50% (15.8 ± 0.6 g versus 35.6 ± 0.8 g in controls), and adipose tissue from treated animals showed increased lipolytic activity. Importantly, and in contrast to chronic treatment with intact hGH, AOD9604 produced no adverse effect on insulin sensitivity as measured by euglycemic clamp — a data point that has shaped how the peptide is framed in subsequent research.
The 2001 Endocrinology study by Heffernan and colleagues extended this work into obese and β3-AR knock-out mice, linking the compound's effects on body weight and fat oxidation to β3-AR expression while dissociating the acute lipolytic response from direct β3-AR activation, as described above.
Cartilage and connective-tissue research
More recent laboratory interest has explored AOD9604 outside of pure metabolic contexts. A 2015 study by Kwon and Park in Annals of Clinical & Laboratory Science evaluated intra-articular AOD9604, with and without hyaluronic acid (HA), in a collagenase-induced knee osteoarthritis model in rabbits. Gross morphological and histopathological scores were significantly higher (worse) in the control group than in the treatment groups, and the combination of AOD9604 with HA was more effective than either agent alone in that model — an example of how the peptide is now used as a research tool in connective-tissue systems as well.
Safety and pharmacokinetic characterization
A 2014 report by Moré and Kenley in the Journal of Endocrinology and Metabolism summarized genotoxicological, toxicological, and pharmacokinetic testing. In that work AOD9604 was reported to be generally well tolerated after chronic oral administration in rats and cynomolgus monkeys, with no evidence of genotoxicity across an Ames test, a chromosomal aberration assay, and a bone-marrow micronucleus assay; orally administered peptide in pigs was absorbed and showed rapid degradation kinetics. These characterizations are part of why AOD9604 is commonly selected as a defined, reproducible research peptide.
How AOD9604 Differs From Full-Length hGH
The distinction most consistently drawn in the literature is that AOD9604 represents only the lipolytic C-terminal domain of hGH. In the reported laboratory systems it did not bind the growth hormone receptor, did not raise IGF-1, and — unlike intact hGH — did not impair insulin sensitivity in the clamp studies. For researchers, this makes AOD9604 useful as a way to study the fat-metabolism-associated signaling of the hGH C-terminus without the confounding growth and glucose effects of the whole hormone.
Storage & Handling
AOD9604 (99%+) is typically supplied as a lyophilized (freeze-dried) powder. For long-term preservation, store the lyophilized peptide at -20°C, protected from light and moisture. Reconstitute immediately prior to use following established laboratory protocols, and avoid repeated freeze-thaw cycles, which can degrade the peptide and compromise its integrity. Reconstituted peptide is generally kept refrigerated and used within a limited window per standard peptide-handling practice.
Conclusion
AOD9604 is a well-studied synthetic fragment of the human growth hormone C-terminus used as a research tool in lipid-metabolism, adipose-tissue, and connective-tissue models. Its interest in the literature stems from reports that it retains hGH-associated lipolytic signaling in laboratory systems without receptor-mediated growth signaling, IGF-1 elevation, or the insulin-sensitivity effects seen with the full hormone. Its mechanisms and downstream targets are still being defined. This product is for research use only and is not intended for human or animal consumption, diagnosis, or treatment.
Frequently Asked Questions
What is AOD9604?
AOD9604 is a synthetic 16-amino-acid peptide (Tyr-hGH 177–191) — residues 177–191 of the C-terminal domain of human growth hormone with an N-terminal tyrosine added; it is also informally called "hGH fragment 176–191." It is studied in laboratory settings as a tool for investigating lipolytic and lipid-metabolism signaling.
Why is AOD9604 studied instead of full human growth hormone?
In published animal and cell studies, AOD9604 reproduced lipolytic-associated activity of hGH without binding the growth hormone receptor or raising IGF-1, allowing researchers to isolate the fat-metabolism signaling of the hGH C-terminus from the hormone's growth-related effects.
What research models has AOD9604 been used in?
Reported models include obese Zucker rats and obese and β3-AR knock-out mice for metabolic work, a collagenase-induced rabbit knee osteoarthritis model for cartilage research, and rat, monkey, and pig systems for safety and pharmacokinetic characterization.
How should AOD9604 be stored?
It is generally supplied lyophilized and stored at -20°C away from light and moisture, reconstituted immediately before use, and protected from repeated freeze-thaw cycles, per standard laboratory peptide-handling protocols.
Is AOD9604 approved for human use?
No. AOD9604 is offered strictly for in-vitro and laboratory research use only. It is not a drug or supplement and is not intended for human or animal consumption, diagnosis, or treatment.