AOD 9604: Research, Mechanism of Action & Scientific Overview

What Is AOD 9604?

AOD 9604 ("Anti-Obesity Drug 9604") is a synthetic 16-amino-acid peptide corresponding to the C-terminal fragment of human growth hormone (residues 177-191) with an additional tyrosine residue added at the N-terminus for stability. It retains the small disulfide loop of the native hormone. It is closely related to, but not identical with, the parent peptide known as hGH fragment 176-191.

Foundational research established that the fat-metabolizing activity of full-length growth hormone resides in a discrete C-terminal structural domain that can be reproduced by a short synthetic peptide. AOD 9604 was built around that finding to isolate the lipolytic (fat-reducing) activity of hGH while leaving behind the anabolic, growth-promoting, and IGF-1-inducing actions that require the intact hormone. AOD 9604 is a research compound and was never approved as a drug.

Key Identifier

Peptide Profile

Full Name: AOD 9604 (Tyr-hGH 177-191)
Structure: Synthetic C-terminal fragment of hGH with an added N-terminal tyrosine; Cys-Cys disulfide loop
Molecular Formula: C₇₈H₁₂₃N₂₃O₂₃S₂ (oxidized form)
Molecular Weight: ~1,815 g/mol
CAS Number: 221231-10-3
Classification: Growth-hormone C-terminal fragment analog

Mechanism of Action

AOD 9604's defining research rationale is that it reproduces the fat-metabolism activity of growth hormone's C-terminus while remaining uncoupled from the hormone's growth and glucose effects.

Lipolytic Activity Uncoupled From Growth Signaling

Foundational work established that the fat-metabolizing activity of full-length hGH is carried by a discrete C-terminal domain, and that a synthetic peptide reproducing that domain retains the activity in isolation. AOD 9604 was designed to mimic this fat-reducing region without reproducing the anabolic, growth-promoting, or IGF-1-inducing actions that require the intact hormone and its receptor.

Stimulation of Lipolysis and Inhibition of Lipogenesis

In vitro and in animal adipose-tissue studies, the C-terminal fragment increased the breakdown of stored lipid (lipolysis) and suppressed the synthesis of new fat (antilipogenic action) in fat cells. The parent synthetic sequence was shown to have antilipogenic activity essentially identical to that of the intact hormone in rodent adipose tissue.

Relationship to the Beta-3 Adrenergic Receptor

A central mechanistic question has been whether the fragment acts through the beta-3 adrenergic receptor (beta-3-AR), the principal lipolytic receptor of fat cells. Research in obese mice found AOD 9604 raised depressed beta-3-AR expression toward lean-animal levels, but knock-out-mouse work concluded the acute lipolytic action is not mediated directly through the beta-3-AR. The peptide's primary molecular target remains formally undefined in the literature.

Metabolic Neutrality (IGF-1 and Glucose)

A repeatedly observed feature is that, unlike full-length hGH, AOD 9604 did not impair carbohydrate metabolism in animal studies and was not associated with the increases in IGF-1 or the insulin resistance seen with growth-hormone administration. This uncoupling of the fat-metabolism effect from the diabetogenic and IGF-1 effects of hGH is the compound's most-cited scientific rationale.

Research Overview

AOD 9604 has a modest but focused peer-reviewed literature spanning adipose biology, animal body-composition work, a human obesity trial program, and later cartilage research. The table below summarizes key areas.

Research Area	Key Findings	Study Type
Lipolysis / Fat Metabolism	The synthetic hGH C-terminal sequence reproduces the antilipogenic activity of intact hGH and stimulates fat breakdown in adipose tissue	In vitro / ex vivo (rodent)
Body Composition	Chronic administration of hGH or its modified C-terminal fragment increased fat oxidation and produced fat loss in obese mice	In vivo (mouse)
Human Obesity Trials	Oral AOD 9604 was advanced through Phase I and Phase II obesity trials; later-stage studies did not reach the efficacy required for drug approval	Randomized controlled trials (human)
Cartilage / Osteoarthritis	Intra-articular AOD 9604, especially combined with hyaluronic acid, enhanced cartilage regeneration in a rabbit osteoarthritis model	In vivo (rabbit)
Metabolic Safety	AOD 9604 did not raise IGF-1 or impair glucose tolerance, contrasting with full-length growth hormone	Animal + human safety data
Oral Bioavailability	Effects on lipid metabolism were observed following oral administration of the synthetic fragment in animals, motivating an oral-formulation path	In vivo (oral dosing)

Research Context

AOD 9604's most robust and distinctive finding is its metabolic neutrality, that it reproduced hGH-like fat effects without the IGF-1 and glucose consequences of the intact hormone. Its human obesity program, however, did not demonstrate the magnitude of weight loss required for approval, and drug development was discontinued. Much of the primary literature comes from a single research program at Monash University and Metabolic Pharmaceuticals.

Common Areas of Research Interest

Research interest in AOD 9604 clusters around fat metabolism and a smaller set of connective-tissue and formulation questions.

Adipose-tissue lipid metabolism, the original and best-characterized focus: lipolysis and inhibition of lipogenesis as an IGF-1-sparing action of the hGH C-terminus
Body-composition and energy-metabolism models, animal studies of fat mass, body-weight trajectory, and fat oxidation under chronic dosing
Metabolic-safety profiling, glucose tolerance, IGF-1 neutrality, and insulin sensitivity as points of contrast with full-length growth hormone
Joint and cartilage research, intra-articular studies of cartilage regeneration, including combination with hyaluronic acid in osteoarthritis models
Delivery and formulation science, oral versus injectable bioavailability, peptide stability, and the role of the N-terminal tyrosine modification
Receptor-pathway biology, the unresolved question of the peptide's primary molecular target and its indirect relationship to beta-3 adrenergic signaling

Pharmacokinetics

AOD 9604 clears from plasma rapidly, yet its metabolic effects in animal models outlasted its circulating half-life, a duration-versus-exposure pattern noted across the research.

~3 min

IV Half-Life (porcine)

1,815

Molecular Weight (Da)

No change

IGF-1 / Glucose

Oral

Route Studied

After intravenous administration the peptide's plasma half-life has been reported at roughly 3 minutes in pig studies, versus about 20 minutes for full-length growth hormone, with clearance proceeding largely through sequential removal of N-terminal residues. Despite this rapid clearance, measurable effects on fat metabolism and body weight in animal models persisted well beyond the circulating half-life, suggesting downstream or adaptive effects rather than sustained plasma exposure.

The development program specifically pursued an oral route, and animal studies demonstrated effects on lipid metabolism after oral dosing. The engineered N-terminal tyrosine and the retained disulfide loop were intended to support peptide stability relative to the unmodified native fragment.

Comparison to Similar Peptides

AOD 9604 is best understood against its parent hormone and the related peptides that act on the growth-hormone axis.

Feature	AOD 9604	Full-Length hGH	Tesamorelin
Origin	Synthetic hGH C-terminal fragment (Tyr-177-191)	Recombinant 191-residue growth hormone	Synthetic GHRH (44-residue) analog
Primary Research Focus	Isolated fat metabolism; also cartilage	Broad growth, anabolism, metabolism	Visceral-fat / lipodystrophy research
Effect on IGF-1	No meaningful increase reported	Raises IGF-1	Raises IGF-1 via the GH axis
Effect on Glucose	Neutral in studies	Can impair glucose tolerance	Can affect glucose via GH axis
Mechanism	Mimics hGH lipolytic domain; IGF-1-sparing	Binds GH receptor; full signaling	GHRH-receptor agonist upstream of hGH

Frequently Asked Questions

What is AOD 9604, and how does it differ from hGH fragment 176-191?

AOD 9604 is a synthetic peptide reproducing the C-terminal lipolytic domain of human growth hormone (residues 177-191) with an added N-terminal tyrosine for stability. The parent fragment 176-191 is the closely related native sequence without that tyrosine. They are near-identical in concept; the tyrosine is the deliberate engineering distinction.

Why was it studied for fat metabolism specifically?

Research established that hGH's fat-reducing activity resides in a discrete C-terminal domain that can be separated from the hormone's growth and IGF-1 effects. AOD 9604 was built to isolate that fat-metabolism activity.

Does it raise IGF-1 or affect blood sugar like growth hormone does?

In the published research it did not raise IGF-1 and did not impair glucose tolerance, a key point of contrast with full-length hGH. This metabolic neutrality is its most-cited scientific feature.

Does it act through the beta-3 adrenergic receptor?

The relationship is indirect and debated. Studies showed AOD 9604 increases beta-3-AR expression, but knock-out-mouse work indicated its acute lipolytic action is not directly mediated by that receptor. Its primary molecular target remains formally undefined.

Is there research beyond fat metabolism?

Yes. The most notable is joint and cartilage research: a rabbit osteoarthritis study found intra-articular AOD 9604, especially combined with hyaluronic acid, enhanced cartilage regeneration.

Was AOD 9604 ever approved as a drug?

No. It reached human obesity clinical trials but did not achieve the efficacy needed for pharmaceutical approval, and development as an anti-obesity drug was discontinued. It is handled today as a research-use-only compound.

Sources & References

Wu Z, Ng FM. "Antilipogenic action of synthetic C-terminal sequence 177-191 of human growth hormone." Biochem Mol Biol Int. 1993;30(1):187-96. PubMed
Ng FM, Jiang WJ, Gianello R, et al. "Molecular and cellular actions of a structural domain of human growth hormone (AOD9401) on lipid metabolism in Zucker fatty rats." J Mol Endocrinol. 2000;25(3):287-98. PubMed
Ng FM, Sun J, Sharma L, et al. "Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone." Horm Res. 2000;53(6):274-8. PubMed
Heffernan MA, Jiang WJ, Thorburn AW, Ng FM. "Effects of oral administration of a synthetic fragment of human growth hormone on lipid metabolism." Am J Physiol Endocrinol Metab. 2000;279(3):E501-7. PubMed
Heffernan MA, Thorburn AW, Fam B, et al. "Increase of fat oxidation and weight loss in obese mice caused by chronic treatment with human growth hormone or a modified C-terminal fragment." Int J Obes Relat Metab Disord. 2001;25(10):1442-9. PubMed
Heffernan M, Summers RJ, Thorburn A, et al. "The effects of human GH and its lipolytic fragment (AOD9604) on lipid metabolism following chronic treatment in obese mice and beta(3)-AR knock-out mice." Endocrinology. 2001;142(12):5182-9. PubMed
Kwon DR, Park GY. "Effect of Intra-articular Injection of AOD9604 with or without Hyaluronic Acid in Rabbit Osteoarthritis Model." Ann Clin Lab Sci. 2015;45(4):426-32. PubMed
Wilding J. "AOD-9604 Metabolic." Curr Opin Investig Drugs. 2004;5(4):436-40. PubMed

Explore AOD 9604

Available for research purposes. Third-party tested for purity and identity.

View AOD 9604 — $80

This product is intended for research and laboratory use only. It is not intended for human consumption.

Disclaimer: This content is provided for educational and informational purposes only. It is not intended as medical advice, nor does it constitute a recommendation for the treatment, cure, or prevention of any disease or condition. AOD 9604 is sold for research purposes only and is not intended for human consumption. Always consult a qualified healthcare professional before making decisions about your health. Somata Peptides does not claim that any products treat, cure, or prevent any disease.

AOD 9604: Growth Hormone Lipolytic Fragment