AOD-9604 peptide explained: what is it and what has research found?

AOD-9604 is often sold today as though its fat loss potential is still an open question. The unusual part of its history is that researchers already took that question into human obesity trials. Early animal work looked promising, several human studies were completed, and then a large phase 2b trial failed to prove that the oral drug worked well enough for obesity. The sponsor stopped that development programme in 2007. ¹

That does not make every piece of AOD-9604 research meaningless. It does mean that claims about human fat loss need to account for the largest clinical test rather than stopping at the earlier animal results.

What is AOD-9604?

AOD-9604 is a synthetic peptide based on amino acids 177 to 191 from the C terminal end of human growth hormone, with an extra tyrosine added at the front of the sequence. The resulting molecule contains 16 amino acids. The idea behind it was to separate some of growth hormone's effects on fat metabolism from the growth promoting effects associated with the intact hormone. ²

That is why AOD-9604 is sometimes described as a growth hormone fragment. It is not full length human growth hormone, and its developers did not intend it to act as a replacement for growth hormone.

The original development theory was attractive: if a short fragment could influence fat metabolism without substantially activating the growth hormone and IGF-1 system, perhaps it could become a weight loss medicine with a different safety profile from full length growth hormone.

Why did researchers think it might reduce body fat?

The case began with preclinical research. Studies in obese rodents reported changes in lipolysis, fat oxidation and body weight after exposure to AOD-9604 or closely related growth hormone fragments. One study in obese Zucker rats found that oral AOD-9604 reduced weight gain and increased lipolytic activity without the reduction in insulin sensitivity seen with intact growth hormone. Animal ³

Another study examined AOD-9604 in obese mice and in mice lacking the beta 3 adrenergic receptor. Chronic treatment reduced body weight and body fat in ordinary obese mice. The receptor knockout experiments suggested that the proposed mechanism was more complicated than simply activating beta 3 adrenergic receptors directly. Animal ⁴

Earlier work also examined the related fragment in obese rodents and isolated human fat tissue. The peptide increased lipolytic activity and reduced lipogenic activity under those experimental conditions. Animal In vitro ⁵

These experiments gave the developers a reason to move into human research. They did not prove that people with obesity would lose a useful amount of weight.

What human studies were carried out?

Between 2001 and 2006, six placebo controlled human studies were conducted as part of the AOD-9604 programme. A later sponsor connected publication reports that 893 adults took part across the six studies. Early trials examined intravenous or oral exposure, tolerability and metabolic markers. The two largest studies were longer oral phase 2b trials. Human ²

The final study, called METAOD006 in that publication, enrolled 502 adults with obesity and lasted 24 weeks. Participants were assigned to oral AOD-9604 tablets or placebo. Human ²

This is important because AOD-9604 was not abandoned before anyone tested it properly in people. It progressed far enough for hundreds of adults to enter a controlled obesity trial.

What did the large obesity trial find?

The decisive result was negative. Metabolic Pharmaceuticals later stated in an Australian Securities Exchange announcement that the large oral phase 2 trial was unable to prove efficacy as an obesity medicine. The company had already terminated the obesity programme in February 2007 because the phase 2b results did not support further clinical development. Human ¹

A later company update described the same programme as having failed to reach its chosen efficacy endpoint. ⁶

That is the most relevant human finding for anyone describing AOD-9604 as a proven fat loss treatment.

Animal studies can show that a mechanism deserves investigation. A large human efficacy study asks whether that mechanism produces a useful result in people. In this case, the programme did not establish the required obesity benefit.

Did an earlier trial look more promising?

There were earlier signs that encouraged continued development. The sponsor later described AOD-9604 as having shown early promise before the large phase 2b result. ⁷

This is a useful example of why later trials matter. Small or early studies can produce encouraging signals. Drug development then moves into larger studies designed to see whether those signals hold up across more people and longer follow up. When the larger trial fails its planned efficacy test, it should carry more weight than an earlier promising result.

That does not prove the molecule has no biological activity. It means the obesity treatment claim did not survive the clinical development programme that was designed to establish it.

Could the oral formulation have been the problem?

The sponsor itself raised that possibility after development stopped. Later company statements suggested that oral delivery of a peptide, changes in formulation and the trial's diet and exercise programme might have contributed to the failure. The company explored whether other routes might deserve investigation. ⁶

That is a hypothesis, not proof that another route works. This distinction matters because much of today's grey market AOD-9604 use involves injection, whereas the obesity programme that tested it used oral administration. A failed oral trial therefore cannot prove that an injectable version is ineffective, but neither can it be used as evidence that injection is effective. A different route requires its own human efficacy and safety evidence.

What do the human studies tell us about safety?

The 2013 safety paper pooled data from the six development studies. The authors reported no significant rise in IGF-1, no clear deterioration in glucose handling and no anti AOD-9604 antibodies in the tested participants. They concluded that the overall tolerability profile in the studied settings was similar to placebo. Human ²

There are reasons to read that reassuring conclusion carefully. Two authors were connected with Metabolic Pharmaceuticals, and the paper states that the company funded the six trials. The studies also do not provide long term exposure beyond the development period, and the substantial obesity trials used oral administration rather than the injectable route commonly discussed today.

The paper itself records adverse events during development, including a severe feeling of chest tightness that investigators considered possibly related during one intravenous study, and diarrhoea considered possibly related during an oral study. Several cancers occurred during one 12 week trial, but the investigators did not consider them treatment related. ²

The FDA later reviewed AOD-9604 for pharmacy compounding and reached a more cautious conclusion. It said available clinical safety information was limited, identified potential concerns involving immune reactions and peptide related impurities, and noted that it had not found human safety information for proposed subcutaneous use. ⁸

So the fairest summary is not that AOD-9604 has no human safety data. It has more human exposure than many grey market peptides. The problem is that the existing data do not establish the safety of the routes, formulations and long term use now promoted outside the original development programme.

What about AOD-9604 for joints and cartilage?

A separate line of research has investigated AOD-9604 in osteoarthritis models. A 2015 rabbit study examined injections into experimentally damaged knee joints. The researchers reported better cartilage and lameness measures with AOD-9604 than saline, with the combination of AOD-9604 and hyaluronic acid performing better than either treatment alone in that animal model. Animal ⁹

That is a real experimental finding, but it is not evidence that AOD-9604 repairs human cartilage. The study involved rabbits with chemically induced osteoarthritis, and the outcome belongs to a different research question from the original obesity programme.

A compound can fail one indication and still deserve investigation for another. Each proposed use has to build its own evidence.

Is AOD-9604 an approved medicine?

No FDA approved medicine contains AOD-9604. In its compounding review, the FDA said neither AOD-9604 free base nor AOD-9604 acetate is a component of an FDA approved drug and concluded that available information raised safety concerns for compounding. ⁸

In the UK, BioRx found no AOD-9604 marketing authorisation in the MHRA public medicines database as of September 2026. The MHRA explains that medicinal products require the appropriate regulatory route and publishes authorised medicine information through its Products service. ^{10 11}

It should therefore be described as an investigational or unapproved peptide, not as an established obesity medicine.

What about competitive sport?

AOD-9604 is explicitly named in the World Anti Doping Agency's 2026 Prohibited List under growth hormone fragments. That section applies at all times, both in and out of competition. ¹²

This status is separate from whether it is effective. A prohibited substance is not automatically a proven performance enhancer or weight loss drug.

Why is AOD-9604 still popular?

Partly because the biological story is easy to understand: take the part of growth hormone linked with fat metabolism, remove the parts associated with growth, and keep the metabolic benefit. It is an attractive idea. The early rodent studies also produced results that are simple to market, while the large negative human trial is less often mentioned because it was not published as a conventional peer reviewed efficacy paper.

That creates an information imbalance. The positive preclinical studies are easy to find in PubMed. The failed obesity result survives mainly in sponsor disclosures and in the later safety paper's description of the development programme.

For readers, the lesson is broader than AOD-9604: the easiest study to find is not always the most important one.

Frequently asked questions

Does AOD-9604 burn fat?

AOD-9604 changed fat metabolism and reduced weight gain in several rodent experiments. Animal ³ The larger human phase 2b obesity trial did not prove the efficacy needed to continue development, so clinically meaningful fat loss in humans has not been established. ¹

Is AOD-9604 the same as human growth hormone?

No. AOD-9604 is a short synthetic fragment derived from the C terminal region of human growth hormone, with an additional tyrosine residue. It does not contain the full growth hormone molecule. ²

Has AOD-9604 been tested in humans?

Yes. The development programme included six placebo controlled studies involving 893 adults according to the sponsor connected safety publication, including a 502 participant phase 2b obesity study. Human ²

Why was AOD-9604 development stopped?

Metabolic Pharmaceuticals stated that its large oral phase 2 obesity trial did not prove efficacy and that the obesity development programme was terminated in February 2007. ¹

Is AOD-9604 approved for weight loss in the UK?

No AOD-9604 marketing authorisation was identified in the MHRA public medicines database when BioRx checked it in September 2026. It should not be presented as an authorised UK weight loss medicine. ¹⁰

More peptide questions

The BioRx conclusion

AOD-9604 is not a peptide with no human research, which is what makes its story useful. Researchers moved from promising animal experiments into a substantial clinical development programme. Hundreds of people received the compound, and the decisive large obesity study did not demonstrate the efficacy needed to take the programme forward. ¹

The evidence therefore supports a more specific conclusion than either extreme. AOD-9604 has genuine biological activity and a real research history, but it has not been shown to be an effective approved human weight loss medicine.

Claims made for injected AOD-9604 today go beyond the route and evidence base of the obesity programme, so they require new human evidence rather than a reinterpretation of old mouse studies.

References

Studies marked "View study in BioRx" sit in the clinical studies index with their design and evidence grade.

1. Metabolic Pharmaceuticals ASX market update, 10 August 2009
2. Stier H, Vos E, Kenley D. Safety and Tolerability of the Hexadecapeptide AOD9604 in Humans
3. Ng FM, Sun J, Sharma L, Libinaka R, Jiang WJ, Gianello R (2000). Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone. Hormone Research.PubMed · DOI · View study in BioRx
4. Heffernan M, Summers RJ, Thorburn A, Ogru E, Gianello R, Jiang WJ, Ng FM (2001). 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.PubMed · DOI · View study in BioRx
5. Heffernan MA, Jiang WJ, Thorburn AW, Ng FM (2000). Effects of oral administration of a synthetic fragment of human growth hormone on lipid metabolism. American Journal of Physiology - Endocrinology and Metabolism.PubMed · DOI · View study in BioRx
6. Calzada shareholder update, 3 June 2011
7. Calzada update on AOD9604, 1 December 2010
8. FDA Pharmacy Compounding Advisory Committee briefing on AOD-9604, 4 December 2024
9. Kwon DR, Park GY (2015). Effect of Intra-articular Injection of AOD9604 with or without Hyaluronic Acid in Rabbit Osteoarthritis Model. Annals of Clinical and Laboratory Science.PubMed · View study in BioRx
10. MHRA Products database
11. MHRA guidance on borderline medicinal products, updated 2 July 2026
12. World Anti Doping Agency, 2026 Prohibited List