Oral AOD9604, a synthetic fragment of growth hormone, reduced weight gain by over 50% in obese rats without impairing insulin sensitivity — unlike full growth hormone.
>50% reduction in weight gainObese rats given oral AOD9604 gained only 15.8 g versus 35.6 g in controls over 19 days — while maintaining normal insulin sensitivity, unlike full growth hormone.
What the researchers found
Oral AOD9604 — a synthetic peptide fragment based on the fat-burning region of human growth hormone — reduced weight gain by over 50% in obese Zucker rats. Treated animals gained only 15.8 g versus 35.6 g in controls over 19 days of daily oral dosing at 500 µg/kg body weight. Fat tissue from treated animals showed increased lipolytic (fat-breaking) activity.
Critically, unlike full-length growth hormone (which is known to worsen insulin resistance with chronic use), AOD9604 showed no adverse effects on insulin sensitivity when tested with euglycemic clamp techniques — considered the gold standard for measuring insulin action. This separation of fat-burning benefits from growth hormone's diabetogenic side effects was the key finding.
Why it matters
Growth hormone has powerful fat-burning effects, but chronic use causes insulin resistance and other serious side effects. AOD9604 represents an attempt to isolate just the fat-burning portion of growth hormone in a smaller, safer peptide. The fact that it worked orally (most peptides are destroyed by digestion) and didn't impair insulin sensitivity made it an attractive candidate for obesity treatment. This early study launched AOD9604 into clinical development and established the rationale behind the peptide's continued popularity in compounding pharmacies.
How the study worked
Obese Zucker rats (a standard model for metabolic obesity) received daily oral doses of AOD9604 at 500 µg/kg body weight for 19 days. Researchers measured body weight gain, fat tissue lipolytic activity, blood glucose, and insulin levels. Insulin sensitivity was assessed using euglycemic clamp techniques, comparing AOD9604-treated animals to both untreated controls and animals treated with intact human growth hormone.
Who was studied
Obese Zucker rats treated with oral AOD9604 for 19 days
What this study cannot tell us
This is a rat study from 2000 — the obese Zucker rat model, while useful, does not fully replicate human obesity. The study was short (19 days) and measured weight gain reduction rather than established fat loss. Sample sizes typical of early preclinical work. Subsequent human clinical trials of AOD9604 failed to show significant weight loss, despite these promising animal results.
How to read the evidence
This is a preclinical rat study from 2000. While the results were promising, subsequent human clinical trials did not replicate the weight loss findings, significantly tempering the evidence base for AOD9604.
When this study was published
Published in 2000, this is a foundational early study on AOD9604. Important context: human clinical trials conducted after this study failed to show significant weight loss, making these rat results historically interesting but not predictive of human outcomes.
The bigger picture
AOD9604 became one of the most talked-about peptides in the weight loss and anti-aging communities, largely based on promising early animal data like this study. However, the story serves as a cautionary tale: despite these strong rat results, subsequent human clinical trials (Phase IIb/III) failed to demonstrate significant weight loss over placebo. The peptide is still widely sold by compounding pharmacies, but its efficacy in humans remains unproven. This 2000 study represents the scientific high point of AOD9604 research.
Questions still open
- Why did AOD9604's impressive fat-burning results in rats fail to translate to significant weight loss in human clinical trials?
- Does AOD9604 have any meaningful metabolic effects in humans at the doses typically used by compounding pharmacies?
- Could the oral bioavailability demonstrated in rats hold up in the different digestive environment of humans?
Common questions
What is AOD9604 and how is it related to growth hormone?
If AOD9604 worked so well in rats, why isn't it an approved weight loss drug?
Read the original research
Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone.
Hormone research, 53(6), 274-8
Citation
Ng, F M; Sun, J; Sharma, L; Libinaka, R; Jiang, W J; Gianello, R. (2000). Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone.. Hormone research, 53(6), 274-8.