# AOD-9604: research overview — Zap Peptides > AOD-9604 is a synthetic hGH C-terminal fragment (residues 177-191) studied for lipolysis and fat oxidation. Data: strong rodent models, null human Phase IIb trial, WADA S2 status. Zap Peptides. Anti-Obesity Drug 9604 — the tyrosine-substituted C-terminal fragment of human growth hormone, studied for lipolysis without GH-receptor engagement. The rodent data were compelling; the human data were not. ## The short version AOD-9604 is a 16-amino-acid synthetic peptide — a *hexadecapeptide* — modelled on the C-terminal portion of human growth hormone. It was engineered to reproduce hGH's fat-burning domain without activating the growth hormone receptor, which means it does not raise IGF-1, does not cause water retention, and does not drive the growth-promoting side effects associated with intact hGH. In obese mice, it reduced body fat and increased fat-burning signals [4][5]. In *humans*, it did not. A clinical programme of roughly 900 subjects across six trials — durations from 7 days to 24 weeks — found that oral AOD-9604 was well tolerated and safe, but failed to produce statistically significant weight loss compared to placebo [3]. The obesity development programme was discontinued after that result. It is not FDA-approved for any indication, and the World Anti-Doping Agency classifies it as a prohibited S2 substance at all times in competition. ## What it is AOD-9604 — formally Anti-Obesity Drug 9604 — is a synthetic analogue of hGH residues 177–191, with a tyrosine substituted for the native phenylalanine at the N-terminus. The reported sequence is YLRIVQCRSVEGSCGF; the two cysteines form an intramolecular disulfide bridge that mirrors the cystine loop of the parent hormone. The molecule was developed by Metabolic Pharmaceuticals (Melbourne) as an oral anti-obesity candidate on the hypothesis that the C-terminal domain of hGH carries its fat-metabolising activity. Non-clinical evaluation found it free of genotoxic and toxicological concerns after chronic oral administration in rats and primates; IV pharmacokinetics showed a half-life of approximately 3 minutes, with in vivo degradation by sequential N-terminal amino-acid removal [2]. It is not a supplement, not a nutraceutical in the conventional sense, and not a DEA-controlled substance. Its 503A compounding status before the FDA Pharmacy Compounding Advisory Committee (docket FDA-2024-N-4777, December 2024) should be independently verified — status as of this writing is not confirmed. ## How it works The mechanistic case for AOD-9604 rests on a series of in vitro and rodent studies characterizing the C-terminal domain of hGH as the portion responsible for lipid metabolism. The foundational mechanism, established in adipocyte and hepatocyte preparations in 1983, is **inhibition of acetyl-CoA carboxylase (ACC)** — the enzyme that catalyzes the first committed step of fatty acid synthesis. The inhibition is indirect: the peptide interacts with plasma-membrane binding sites and releases a second messenger that increases ACC phosphorylation and inactivation, thereby suppressing *de novo* lipogenesis [7]. Subsequent rodent work characterized AOD-9604 as a synthetic lipolytic/antilipogenic domain of hGH, localizing fat-metabolism activity to this C-terminal region [6]. In obese mice treated chronically with AOD-9604, body fat was reduced and **beta-3 adrenergic receptor (beta3-AR) expression** in white adipose tissue was increased [4]. The beta3-AR is a key regulator of thermogenesis and lipolysis in adipocytes. Knockout studies clarified the dependency: chronic fat loss required functional beta3-AR signaling, while acute increases in fat oxidation and energy expenditure persisted even without it [4]. A companion study confirmed the fat-oxidation and weight-loss effect in obese mice [5]. The growth-hormone receptor is not engaged by AOD-9604, which is why it does not raise IGF-1 or produce the tissue-building and fluid-retaining effects of intact hGH — this receptor-sparing design was the drug's central engineering rationale [6]. ## What the research shows The evidence base is a clear two-tier story: animal models supported the mechanism; human trials did not deliver a clinical endpoint. **Rodent and cell data (supportive)** Multiple studies in obese mice documented reduced body weight and fat mass, increased fat oxidation, and elevated beta3-AR expression following chronic AOD-9604 administration [4][5][6]. The acetyl-CoA carboxylase inhibition mechanism was demonstrated in adipocyte and hepatocyte preparations [7]. A collagenase-induced knee osteoarthritis model in 32 New Zealand white rabbits showed reduced cartilage degeneration scores after intra-articular injection — a secondary line of research unrelated to the primary obesity program [1]. **Human data (negative for primary endpoint)** Stier et al. (2013) summarized the full human clinical programme: approximately six trials, roughly 900 obese subjects, oral doses ranging from 0.25 mg to 54 mg daily, durations from 7 days to 24 weeks [3]. Safety and tolerability were indistinguishable from placebo across the programme. **The primary obesity endpoint — statistically significant weight loss versus placebo — was not met.** The development programme was discontinued circa 2007. No published peer-reviewed report of a positive human weight-loss signal from AOD-9604 in a placebo-controlled trial has been identified. A non-clinical safety review (2014) confirmed no genotoxic or toxicological concerns after chronic oral dosing in rats and primates, and characterized the very short IV half-life (~3 minutes) with in vivo degradation by N-terminal amino acid removal [2]. **Evidence tier:** Mechanism established in vitro and in rodent models. Human translation: no efficacy signal in placebo-controlled trials. The preclinical-to-human gap for this compound is large and documented. ## Reported effects, cautions & safety The following community reports are **anecdotal, not clinical evidence**. They are included because they represent the pattern of real-world experience reported in peptide research communities — and because the gap between those reports and the published human evidence is itself informative. **Community signals:** - *No noticeable fat loss* is the most common report — consistent with the null human trials [3]. - *Well tolerated overall*: most report few side effects, matching the published finding of placebo-equivalent tolerability [3]. - *No GH-type side effects* (no water retention, no joint puffiness, no IGF-1 effects) — consistent with the receptor-sparing design. - *Mild energy lift or sense of well-being*: a minority report, not supported by any trial endpoint, plausibly attributable to concurrent lifestyle changes. - *Local injection-site redness or irritation*: occasional, generic to subcutaneous peptide injection. - *Claims of localized fat loss*: anecdotal and biologically implausible; spot lipolysis by injection site is not supported by physiology or any human trial. **Published safety cautions:** AOD-9604 is not FDA-approved and carries no approved indication, dosing standard, or quality control requirement for human use [3]. The human weight-loss efficacy signal was not demonstrated in the pivotal trial programme [3]. The fat-metabolism mechanisms — ACC inhibition, beta3-AR upregulation, increased fat oxidation — were characterized primarily in mouse, rat, and cell models, and these mechanistic findings did not translate into a proven human fat-loss effect [6][4]. The rodent-to-human translational gap for this compound illustrates a general pattern in obesity pharmacotherapy [6]. Long-term human safety data beyond 24 weeks does not exist in the published literature [3]. Subcutaneous human pharmacokinetics have not been published in peer-reviewed literature. **Regulatory caution:** AOD-9604 is classified under **WADA Prohibited List Section S2** (Peptide Hormones, Growth Factors, Related Substances and Mimetics) as a growth-hormone fragment and is prohibited at all times in sport. Dedicated anti-doping assays can detect it even though it does not interfere with the standard hGH isoform immunoassay. ## Where it fits in the metabolic picture Among the three compounds on this desk, AOD-9604 occupies a distinctive position: the most mechanistically studied for pure lipolysis, and the one with the clearest negative human result. The ACC inhibition and beta3-AR upregulation mechanisms are real — the question the human trials answered is whether those mechanisms, at the doses achievable in people, produce a clinically meaningful fat-loss effect. The answer from the Phase IIb programme is that they do not, at least not to a statistically significant degree in the studied population. For the researcher comparing approaches to metabolic intervention, AOD-9604 is a case study in how compelling preclinical mechanism does not guarantee clinical translation — a pattern noted in reviews of obesity pharmacotherapy [6]. Tirzepatide, reviewed on the adjacent [tirzepatide page](/tirzepatide), represents the opposite trajectory: a mechanism (dual incretin agonism) that survived human Phase 3 testing at scale. MOTS-c sits at an earlier stage still: mechanism characterized in cells and animals, human interventional data absent [see /mots-c]. --- A numerically honest digest of the published evidence — effect sizes, study designs, and the gaps between them.