Category: Research Summaries

What This Article Covers

AOD-9604 is a synthetic peptide fragment based on the C-terminal region of human growth hormone. It was studied because researchers wanted to separate one part of growth hormone biology – fat metabolism – from the broader growth-promoting and IGF-1-linked effects of the full hormone.

The useful question is not simply whether AOD-9604 has been studied. It has. The better question is: what was actually tested, in which models, and what did the results show?

Bottom Line

The human record for AOD-9604 is mixed in a very specific way. Safety and tolerability looked generally favorable in the published clinical safety summary, especially for the endpoints that matter when comparing it with full-length growth hormone: IGF-1, glucose handling, insulin-related measures, antibodies, vital signs, ECGs, and standard laboratory markers. But the human efficacy story is much weaker. Small early studies showed short-term fat-metabolism marker changes, but larger obesity studies did not establish a clear, clinically meaningful weight-loss effect versus placebo.

That makes AOD-9604 a good example of a compound where the animal and mechanistic evidence is interesting, but the human outcome evidence does not support broad claims.

What Was Tested in Humans?

The main published clinical safety paper summarized six randomized, double-blind, placebo-controlled human trials involving AOD-9604. According to that paper, approximately 900 adults participated across the program. Most were adults with obesity, although the earliest trial included healthy adult male volunteers. The study designs included single-dose IV studies, single-dose oral studies, a short 7-day oral multiple-dose study, and two longer oral studies in adults with obesity.

1. Single-dose IV studies

In early IV studies, AOD-9604 was tested as single infusions in healthy men and in men with obesity. The doses ranged from 25 mcg/kg to 400 mcg/kg in the healthy-volunteer study, and 25, 50, and 100 mcg/kg in the obese-subject study. These were safety and tolerability studies, not mature weight-loss trials.

The safety findings were relatively clean. The published summary reported no clinically significant changes in vital signs, physical examination findings, clinical laboratory parameters, ECG, glucose, or IGF-1. In the obese-subject IV study, headache was common, and a few adverse events were rated severe, including one chest-tightness event considered possibly related to treatment. Mild or moderate euphoria was also reported during AOD-9604 periods in some subjects, but the overall adverse-event pattern did not show a clear dose trend.

The FDA’s 2024 briefing document summarized an early IV obesity study slightly differently from a clinical-effectiveness angle: 23 adults with obesity had a short-term increase in non-esterified fatty acids, a marker related to fat metabolism, but the average weight change over three weeks was not statistically different from placebo.

2. Single-dose and short oral studies

A small oral study tested single oral doses of 9, 27, and 54 mg AOD-9604 in clinically obese men. The published safety summary reported no meaningful changes in IGF-1 and no clinically significant trends in vital signs, ECG, or safety laboratory findings. Gastrointestinal events such as diarrhea, flatulence, increased appetite, and nausea appeared among the common adverse events.

From the effectiveness side, FDA summarized the small oral study as showing a rise in non-esterified fatty acids at about four hours, but no statistically significant weight loss compared with placebo. That is the key distinction: a marker moved, but the endpoint people care about – weight loss versus placebo – was not established.

A 7-day multiple-dose oral study tested daily AOD-9604 in obese men. Safety again looked generally similar to placebo, except that the highest oral dose group had more headache, diarrhea, and flatulence. FDA’s briefing noted a reported 1 kg average weight loss at one dose versus 0.6 kg in placebo over one week, but also noted that the publication gave very limited details and did not provide enough information to support a strong conclusion.

3. Longer oral studies

The longer studies are where the story becomes clearer.

One 12-week randomized, double-blind, placebo-controlled multicenter study included 300 adults with obesity and tested daily oral doses of 1, 5, 10, 20, or 30 mg AOD-9604 versus placebo. The published safety summary reported no significant changes in IGF-1, no obvious glucose-tolerance signal, no anti-AOD-9604 antibodies, and no meaningful trends in standard laboratory markers, vital signs, or ECGs. FDA noted that an abstract from this study reported greater weight and waist reduction than placebo, but the differences were small, the dose response was not straightforward, and the abstract did not provide enough detail to interpret the result confidently.

A later Phase IIb obesity trial was the most important human outcome test. FDA’s 2024 briefing document states that Metabolic Pharmaceuticals’ larger study enrolled more than 500 patients with obesity and did not find a significant difference in weight loss after 12 weeks, which was the primary endpoint. The company publicly announced in 2007 that the Phase IIb results did not support commercial viability as an obesity treatment and terminated development for that use.

What Did Human Studies Actually Show?

• Safety/tolerability: In the published clinical safety summary, AOD-9604 looked broadly similar to placebo across the studied oral and IV protocols. The authors reported no treatment-related withdrawals or serious adverse events, no meaningful IGF-1 increase, no deterioration in glucose handling, and no detected anti-AOD-9604 antibodies in tested subjects.
• Fat-metabolism markers: Some small early studies reported short-term increases in non-esterified fatty acids, a marker associated with fat mobilization. That is biologically interesting, but it is not the same as proving clinically meaningful weight loss.
• Weight-loss efficacy: The human evidence does not establish AOD-9604 as an effective obesity treatment. FDA’s review states that most identified studies failed to show benefit versus placebo and that a larger Phase IIb program failed its primary weight-loss endpoint.
• Route gap: FDA did not identify human exposure data for the proposed subcutaneous or topical routes reviewed in the 2024 compounding context. Most human study information involved oral or IV administration.

What Did Animal and Cell Studies Show?

The preclinical record explains why AOD-9604 was worth testing in humans in the first place.

In obese Zucker rats, daily oral AOD-9604 for 19 days reduced body-weight gain compared with control animals and increased lipolytic activity in adipose tissue. The same study reported no adverse effect on insulin sensitivity in that animal model, unlike what can be seen with intact growth hormone.

In obese mice, chronic treatment with human growth hormone or AOD-9604 reduced body-weight gain, increased fat oxidation, and increased plasma glycerol, a marker of lipolysis. Importantly, AOD-9604 did not compete for the growth-hormone receptor and did not induce growth-hormone-receptor-mediated cell proliferation in the assay used. That supports the idea that this fragment does not behave like full-length growth hormone in every respect.

Another mouse study looked at obese mice and beta-3 adrenergic receptor knockout mice. In ordinary obese mice, AOD-9604 reduced body weight and body fat after chronic treatment and increased beta-3 adrenergic receptor RNA expression in adipose tissue. In beta-3 receptor knockout mice, the chronic weight and lipolysis responses were not seen in the same way, although acute AOD-9604 still increased energy expenditure and fat oxidation. The authors concluded that AOD-9604’s lipolytic actions were not mediated directly through beta-3 adrenergic receptors, even though changes in that pathway may contribute to altered lipolytic sensitivity.

How the Animal Evidence Relates to the Human Evidence

The animal data creates a plausible mechanism: AOD-9604 can affect lipid metabolism, fat oxidation, and lipolysis in obese rodent models without clearly activating the classic growth-hormone/IGF-1 pathway. That mechanistic profile explains why researchers moved it into human obesity studies.

But translation is the hard part. In humans, short-term metabolic markers moved in some small studies, but those signals did not mature into a convincing weight-loss result in the larger obesity program. In plain English: the animal work says there was a reasonable scientific reason to test AOD-9604; the human program says the test did not deliver strong obesity efficacy.

What Is Not Established

• AOD-9604 is not established as an effective human weight-loss treatment.
• The published human safety summary does not prove safety for all routes, formulations, concentrations, populations, or long-term exposure scenarios.
• Animal fat-metabolism findings should not be presented as proven human outcomes.
• Analytical and anti-doping detection studies help identify the compound and its metabolites; they do not establish clinical benefit.
• FDA did not identify human data for subcutaneous or topical AOD-9604 in the 2024 compounding review context.

Research-Use Boundary

This article summarizes published research and regulatory-source discussion for technical review. It is not medical advice, not a dosing guide, and not a recommendation for human or veterinary use. KRL materials are sold for research use only and are not for diagnostic, therapeutic, or administration purposes.

Selected Sources

• Stier H, Vos E, Kenley D. Safety and Tolerability of the Hexadecapeptide AOD9604 in Humans. Journal of Endocrinology and Metabolism. 2013.
• FDA Pharmacy Compounding Advisory Committee Briefing Document for AOD-9604 Related Bulk Drug Substances. December 4, 2024.
• Heffernan MA, 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. International Journal of Obesity. 2001.
• Heffernan M, 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.
• Ng FM, et al. Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone. Hormone Research. 2000.
• Cox HD, et al. Detection and in vitro metabolism of AOD9604. Drug Testing and Analysis. 2015.

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