AOD-9604

AOD-9604 (Anti-Obesity Drug-9604) is a synthetic 16-amino-acid peptide fragment corresponding to residues 176-191 of the C-terminal region of human growth hormone (hGH), commonly referred to in the literature as “hGH Fragment 176-191” or “AOD9604.” The sequence is modified from the native hGH fragment by substitution of a tyrosine for the terminal phenylalanine, a change made to improve stability without altering the fragment’s biological activity. Its full sequence is: Tyr-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe.

The compound originates from work by Professor Frank Ng and colleagues at Monash University, Australia, in the 1990s, who were investigating which portion of the full 191-amino-acid hGH molecule was responsible for its lipolytic (fat-mobilising) activity as distinct from its growth-promoting activity. Earlier research had shown that a C-terminal fragment of hGH retained the hormone’s ability to stimulate lipolysis and inhibit lipogenesis in adipocytes without the growth-stimulating, insulin-desensitising, or diabetogenic effects associated with the intact hormone, which are mediated principally through IGF-1 signalling. AOD-9604 was engineered specifically to isolate this metabolic fragment, with the aim of separating hGH’s fat-metabolising properties from its growth-hormone and IGF-1-linked effects.

The compound was subsequently licensed to Metabolic Pharmaceuticals Ltd (Australia), which advanced it through preclinical development and six human clinical trials, making AOD-9604 one of the few peptides in this general research category with a substantial body of published human trial data, primarily generated in pursuit of an anti-obesity drug candidate during the 2000_s.

1. Beta-3 Adrenergic Receptor-Mediated Lipolysis

The principal proposed mechanism for AOD-9604 is stimulation of lipolysis via beta-3 adrenergic receptors (β3-AR) expressed on adipocytes, rather than through the growth hormone receptor or IGF-1 axis. Heffernan and colleagues, working with β3-AR knockout mice, showed that both intact hGH and AOD-9604 elevated suppressed β3-AR mRNA expression in obese mice toward levels seen in lean controls, and that in β3-AR knockout animals, the lipolytic and body-weight effects observed with AOD-9604 in wild-type mice were abolished. This supports β3-AR as a necessary mediator of the fragment’s activity in the mouse model.

2. cAMP-Hormone-Sensitive Lipase Activation

Downstream of β3-AR engagement, the proposed pathway follows the canonical adrenergic lipolytic cascade: receptor activation stimulates adenylate cyclase, raising intracellular cAMP, which activates protein kinase A and subsequently hormone-sensitive lipase (HSL), driving hydrolysis of stored triglycerides into free fatty acids and glycerol.

3. IGF-1-Independent Action

A defining feature distinguishing AOD-9604 from full-length hGH is that its lipolytic activity is not accompanied by a rise in circulating IGF-1. Because IGF-1 elevation underlies most of the adverse metabolic effects associated with growth hormone therapy (insulin resistance, edema, joint pain, and theoretical concerns about growth-promoting effects on non-adipose tissue), this dissociation was the central pharmacological rationale for developing AOD-9604 as a targeted metabolic agent rather than using intact hGH.

Animal Studies

In obese rodent models, chronic administration of AOD-9604 produced reductions in body fat and improved measures of lipid metabolism comparable in magnitude to those produced by full-length hGH, without the accompanying elevation in IGF-1 or impairment of glucose tolerance seen with intact hGH treatment. As above, effects were lost in β3-AR knockout mice, supporting receptor-specific action rather than a generalised metabolic effect.

Human Clinical Studies

AOD-9604 is unusual among the compounds discussed on this site in having a substantial published human clinical trial record. Six randomized, double-blind, placebo-controlled studies enrolling a combined total of roughly 900 adult subjects were conducted by Metabolic Pharmaceuticals during the 2000s.

Early dose-ranging and proof-of-concept trials reported modest but statistically significant weight loss at some doses; in one such trial, subjects receiving 1 mg/day of AOD-9604 lost approximately 2.6 kg over the study period compared with roughly 0.8 kg in the placebo group. Across the acute dose-escalation safety trials (designated METAOD001-METAOD003), no adverse events attributable to AOD-9604, no withdrawals due to the drug, and no serious adverse events were reported; the safety profile was described as indistinguishable from placebo.

However, the pivotal Phase IIb trial (METAOD006, the “OPTIONS” study), a larger randomized, double-blind, placebo-controlled trial of roughly 536 obese subjects across multiple dose arms (0.25, 0.5, and 1 mg/day) conducted with a structured diet-and-exercise background, did not replicate a statistically significant weight-loss benefit over placebo at the primary endpoint. This result, following the earlier positive signal, led Metabolic Pharmaceuticals to discontinue the formal pharmaceutical development program for obesity in 2007. Weight-loss efficacy findings across the AOD-9604 human trial program are therefore best described as inconsistent, with the largest, most rigorously controlled trial failing to confirm the effect suggested by smaller earlier studies.

Separately, AOD-9604 received Generally Recognized As Safe (GRAS) status from the US FDA for use as an ingredient in conventional foods, a food-safety classification, not a drug approval, and not an endorsement of efficacy for any therapeutic or weight-management claim.

AOD-9604 is one of the better-characterised compounds in this category with respect to human safety data, owing to its formal drug-development history. Across the six completed human trials, no serious adverse events attributable to the compound were reported, and its tolerability profile was reported as comparable to placebo. Confirming its mechanistic rationale, treatment did not raise serum IGF-1 levels, and oral glucose tolerance testing showed no adverse effect on carbohydrate metabolism, in contrast to the known effects of full-length hGH. No anti-AOD-9604 antibodies were detected in patients assessed for immunogenicity. Notwithstanding this relatively favourable record for a peptide reaching Phase IIb, this data was generated for a specific development program (obesity treatment under medical supervision) using pharmaceutical-grade material under controlled dosing; it does not constitute a general safety endorsement for uncontrolled or research settings, and long-term safety data beyond the trial periods are not available.

AOD-9604 is a well-studied hGH-derived peptide fragment with a clear, mechanistically supported rationale: isolating the lipolytic, β3-adrenergic-receptor-mediated activity of growth hormone from its IGF-1-linked growth-promoting and diabetogenic effects. Preclinical rodent data and the β3-AR knockout experiments provide reasonably strong mechanistic support, and the compound’s human safety record, drawn from six clinical trials and roughly 900 subjects, is more extensive than that available for most comparable research peptides. Its efficacy record, however, is mixed: modest, statistically significant weight loss was observed in early smaller trials, but the pivotal, larger Phase IIb trial did not confirm a significant benefit over placebo, and formal pharmaceutical development for obesity was discontinued in 2007. AOD-9604 is not an approved medicine for weight loss or any other indication in any jurisdiction; it holds FDA GRAS status only as a food ingredient. It remains available as a research-use-only compound, and any conclusions about efficacy in humans should reflect the genuinely inconsistent trial record rather than the more favourable early results in isolation.

Ng FM, et al. Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone. Hormone Research. 2000.

Heffernan M, et al. The effects of human GH and its lipolytic fragment (AOD9604) on lipid metabolism following chronic treatment in obese mice and β3-AR knock-out mice. Endocrinology.

Stier H, Vos E, Kenley D. Safety and Tolerability of the Hexadecapeptide AOD9604 in Humans. J Endocrinol Metab. 2013.

Moré MI, et al. Safety and Metabolism of AOD9604, a Novel Nutraceutical Ingredient for Improved Metabolic Health. J Endocrinol Metab.

1. Ng FM, Sun J, Sharma L, Libinaka R, Jiang WJ, Gianello R. Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone. Horm Res. 2000;53(6):274-278. doi: 10.1159/000053183.

2. 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):1442-1449. doi: 10.1038/sj.ijo.0801740.

3. 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 β3-AR knock-out mice. Endocrinology. 2001;142(12):5182-5189. doi: 10.1210/endo.142.12.8522.

4. Wang MY, Bhatt A, et al. Physiology and pharmacology of adipocyte β3-adrenergic receptor lipolytic signalling. Review, various sources.

5. Ng FM, et al. Effects of a synthetic hGH fragment (AOD9604) on IGF-1 and glucose metabolism relative to intact hGH. Horm Res. 2000;53(6). doi: 10.1159/000053183.

6. Stier H, Vos E, Kenley D. Safety and Tolerability of the Hexadecapeptide AOD9604 in Humans. J Endocrinol Metab. 2013;3(1-2):55-62. doi: 10.4021/jofem157w.

7. Metabolic Pharmaceuticals Ltd. The effect of AOD9604 on weight loss in obese adults: results of a randomized, double-blind, placebo-controlled, multicenter study. Clinical trial report / journal publication, early 2000s.

8. Metabolic Pharmaceuticals Ltd. METAOD006 (OPTIONS study) Phase IIb randomized, double-blind, placebo-controlled trial of AOD9604 in obese adults. Company clinical trial disclosure, 2007.