AOD 9604: The hGH Fragment Studied for Fat Metabolism

AOD 9604 is a synthetic peptide made from the C-terminal end of human growth hormone, amino acids 176 to 191, with an extra tyrosine added for stability. It was developed at Monash University and by Metabolic Pharmaceuticals in Melbourne as an anti-obesity drug (the name stands for Anti-Obesity Drug 9604) on the theory that this small fragment carries the fat-metabolising activity of growth hormone without its growth-promoting effects. Mouse studies supported the idea; a large phase 2b obesity trial in the mid-2000s did not meet its primary weight-loss endpoint and development stopped. In the UK, AOD 9604 has no MHRA marketing authorisation and is sold only as a research chemical.

This guide explains where AOD 9604 came from, what the animal and human research reported, why it is still of interest to laboratories despite the failed obesity programme, and what UK researchers should check before buying it.

What is AOD 9604?

Human growth hormone is a 191-amino-acid protein with many effects, including stimulating IGF-1 production, promoting tissue growth, raising blood glucose and increasing the breakdown of stored fat (lipolysis). In the 1990s a group led by Frank Ng at Monash University set out to isolate the region of the molecule responsible for the lipolytic effect. Their candidate was the C-terminal region, residues 176 to 191, which they synthesised as a short peptide and modified with an N-terminal tyrosine to make it more stable. The resulting 16-amino-acid sequence is AOD 9604, sometimes written AOD9604 or referred to as hGH fragment 176-191.

The important design point is what the fragment does not do. Because it lacks the parts of growth hormone that bind the growth hormone receptor in the usual way, it was expected to have no effect on IGF-1, blood glucose or cell proliferation. That expectation was later borne out in the human safety data, and it is the reason the compound is of continuing interest as a research tool: it separates one activity of growth hormone from the rest.

What the animal research reported

The preclinical literature comes mainly from the Monash group in the late 1990s and early 2000s. Ng and colleagues, in a 2000 paper in Hormone Research, described the metabolic effects of the synthetic lipolytic domain of growth hormone in obese rodents. Heffernan and colleagues followed in 2001 with work in obese (ob/ob) mice, published in Endocrinology and the International Journal of Obesity, reporting that chronic treatment with either full-length growth hormone or the fragment increased fat oxidation and reduced weight gain, and that the fragment did so without raising IGF-1 or impairing glucose handling.

The same group proposed a mechanism. In beta3-adrenergic receptor knockout mice the fragment lost its effect on fat oxidation, which suggested it acts at least partly through beta3-adrenergic signalling in fat tissue rather than through the growth hormone receptor. This is a plausible route, since beta3 receptors are involved in lipolysis and thermogenesis in rodents, though it is worth remembering that beta3-adrenergic pharmacology translates poorly from mice to humans, which may be one reason the clinical results looked different.

What the human trials reported

Metabolic Pharmaceuticals took AOD 9604 into clinical development in the early 2000s. A 12-week phase 2a study in obese adults, announced by the company in 2004, reported a modest average weight loss on the lowest dose compared with placebo, which was enough to justify a larger trial. The pivotal phase 2b study, a randomised, placebo-controlled trial in over 500 obese adults at several doses, then failed to show a statistically significant weight-loss difference from placebo at its primary endpoint. The company announced in 2007 that it would not take the obesity programme forward, and the full phase 2b results were never published in a peer-reviewed journal.

What did get published was the safety data. Stier, Vos and Kenley pooled results from six clinical trials, covering more than 900 participants, in a 2013 paper in the Journal of Endocrinology and Metabolism. They reported that AOD 9604 was well tolerated, that the adverse-event profile was similar to placebo, and that there was no evidence of increased IGF-1, altered glucose tolerance or antibody formation. On the strength of that data the compound was self-affirmed as GRAS (generally recognised as safe) as a food ingredient in the United States in 2013, a regulatory route that is unrelated to medicines licensing and has no equivalent in the UK.

Why AOD 9604 is still studied

A failed obesity drug might seem an odd thing for a laboratory to want, but AOD 9604 has three properties that keep it useful. It is a clean tool for asking which effects of growth hormone are separable from IGF-1 signalling. It has an unusually large human safety dataset for a research peptide. And the cartilage work opened a second line of enquiry: Kwon and Park reported in 2015 that intra-articular injection of AOD 9604, alone or with hyaluronic acid, improved cartilage histology in a rabbit model of osteoarthritis, and later small animal studies have looked at tendon and joint tissue.

• Adipocyte and fat-tissue models examining lipolysis, beta3-adrenergic signalling and fat oxidation independently of the growth hormone receptor.
• Comparative studies against growth hormone secretagogues such as CJC-1295, ipamorelin and tesamorelin, which act upstream by raising endogenous growth hormone.
• Cartilage, tendon and joint models following the osteoarthritis work.
• Analytical and stability work, since the short sequence is easy to characterise by HPLC and mass spectrometry.

Is AOD 9604 legal in the UK?

AOD 9604 is legal to buy, sell and possess in the UK as a research chemical. It is not a controlled substance under the Misuse of Drugs Act 1971. It has no marketing authorisation from the MHRA, so it cannot lawfully be supplied for human medicinal use or marketed with medicinal claims under the Human Medicines Regulations 2012. The GRAS status it holds in the United States does not carry over to the UK and does not make it a food or a supplement here.

Anyone involved in competitive sport should also know that AOD 9604 is prohibited by the World Anti-Doping Agency under the category of peptide hormones, growth factors and related substances. It became widely known in the UK and Australia through the 2013 Essendon Football Club supplements case, which is where much of the public awareness of the compound comes from.

AOD 9604 vs growth hormone secretagogues

Researchers sometimes group AOD 9604 with CJC-1295, ipamorelin and tesamorelin because all four are connected to growth hormone. The mechanisms are different. The secretagogues act on the pituitary to increase the release of the body's own growth hormone, which in turn raises IGF-1. AOD 9604 is a piece of the growth hormone molecule itself, engineered so that it does not raise IGF-1 at all. In a study design, that makes it the control for growth-hormone-independent fat effects rather than a substitute for the secretagogues. Our guide to CJC-1295, ipamorelin and tesamorelin covers the secretagogue side in detail.

What to check before buying AOD 9604 in the UK

AOD 9604 is a short, unmodified peptide and therefore relatively cheap to make, which means it is widely available and quality varies. A 20mg research pen from a UK supplier typically costs in the region of £65. Because it is inexpensive, corners are more likely to be cut on testing than on synthesis, so the certificate of analysis is the main thing to look at.

1. Ask for a batch-specific certificate of analysis with HPLC purity and mass spectrometry identity. Calibre pens are tested by Janoshik Analytical and COAs are published on the site's COA page.
2. Check that the sequence on the COA includes the N-terminal tyrosine; hGH 176-191 without it is a different compound.
3. Confirm the purity target is above 99% and the stated quantity is peptide content, not gross pen weight.
4. Choose a pre-filled, precision-made pen if your protocol needs consistent volumes rather than reconstitution.
5. Store refrigerated and away from light; read our guide to storing peptide pens for the practical details.

Summary

AOD 9604 is a 16-amino-acid fragment of human growth hormone that was designed to carry the lipolytic activity of the parent hormone without affecting IGF-1 or glucose. Rodent studies supported the concept, human trials confirmed it was well tolerated, and the largest obesity trial failed to show a significant effect on weight. It remains a useful research tool for separating growth hormone activities and for joint-tissue models. In the UK it is legal as a research chemical, has no MHRA authorisation, and should be bought only with a batch-specific certificate of analysis.