Retatrutide vs AOD-9604.

Retatrutide (development code LY3437943) is an investigational once-weekly injectable peptide developed by Eli Lilly for the treatment of obesity and related cardiometabolic disease. It is a single synthetic peptide engineered to act as a "triple G" agonist, simultaneously stimulating three nutrient-hormone receptors: the glucagon-like peptide-1 (GLP-1) receptor, the glucose-dependent insulinotropic polypeptide (GIP) receptor, and the glucagon receptor. This distinguishes it from the single agonist semaglutide (GLP-1) and the dual agonist tirzepatide (GIP/GLP-1), both already approved.

AOD-9604 ("Advanced Obesity Drug 9604") is a synthetic 16-amino-acid peptide corresponding to the C-terminal lipolytic region of human growth hormone (hGH), residues 177–191, with an added tyrosine at the N-terminus. It was engineered in the 1990s by researchers at Monash University and developed by the Australian biotech Metabolic Pharmaceuticals as an orally-investigated anti-obesity agent. The design goal was to isolate hGH's fat-mobilizing activity while leaving out the growth-promoting, IGF-1-stimulating actions of the full hormone.

Retatrutide is a balanced agonist at three receptors, each contributing a distinct metabolic effect. GLP-1 receptor agonism enhances glucose-dependent insulin secretion, slows gastric emptying, and acts centrally to reduce appetite and food intake. GIP receptor agonism further modulates insulin response and appears to improve nutrient handling and tolerability. The defining addition is glucagon receptor agonism, which raises hepatic glucose output and, importantly, increases energy expenditure and promotes hepatic lipid oxidation/mobilization. The combination is intended to layer glucagon-driven increases in energy expenditure and reductions in liver fat on top of the appetite suppression and glycemic benefits of incretin (GLP-1/GIP) signaling. Because glucagon agonism can raise hepatic glucose production and resting heart rate, the receptor balance and dose are designed to keep net effects metabolically favorable.

In rodent models, AOD-9604 reproduces the lipolytic (fat-breakdown) and fat-oxidation–promoting effects of full-length growth hormone without binding the GH receptor and without raising IGF-1. Mechanistic work in obese and beta-3-adrenergic-receptor knockout mice indicated its effect on fat metabolism is associated with modulation of beta-3 adrenergic receptor activity and increased lipolysis and fat oxidation rather than classic GH-receptor signaling. Because it does not engage the GH receptor, it was hypothesized to avoid the insulin-resistance and tissue-growth liabilities of GH itself. Importantly, the cleanly receptor-independent, IGF-1-sparing profile is best characterized in animal and in-vitro work, not firmly established in humans.

Human evidence comes from a completed Phase 2 program and emerging Phase 3 data, so this is no longer animal-only, though long-term outcome and safety data remain immature. In the 48-week Phase 2 obesity trial (Jastreboff et al., NEJM 2023), adults with obesity/overweight without diabetes had least-squares mean weight reductions of roughly -17.1%, -22.8%, and -24.2% across higher dose groups versus -2.1% with placebo. A parallel Phase 2 trial in type 2 diabetes (Rosenstock et al., Lancet 2023) showed substantial reductions in HbA1c and body weight. A Phase 2a trial in metabolic dysfunction-associated steatotic liver disease (Nature Medicine 2024) reported large relative reductions in liver fat, with the majority of higher-dose participants reaching liver fat below the steatosis threshold. In May 2026 Lilly reported topline Phase 3 results (TRIUMPH-1, ~2,339 adults), with the highest dose producing about 28.3% mean weight loss at 80 weeks; full peer-reviewed Phase 3 publications and the broader TRIUMPH cardiovascular/diabetes outcome trials were still pending at that time.

Preclinical evidence is the strongest part of the AOD-9604 record: chronic dosing reduced body-weight gain and increased fat oxidation in obese mice (Heffernan et al., Int J Obes, 2001; PMID 11673763). It progressed into human obesity trials in the early-mid 2000s; a 12-week randomized study reported only a modest separation from placebo (on the order of ~1–2 kg), and development was halted around 2007 after a larger ~24-week trial failed to show meaningful weight-loss efficacy, particularly once diet and exercise were standardized. No peer-reviewed pivotal trial demonstrates clinically useful weight loss, and there is no robust human evidence for the commonly marketed claims around cartilage, joint, or tendon repair: those rest on limited preclinical/early work. In short, the human data are negative-to-thin for obesity and largely absent for other indications.

In trials the most common adverse events were gastrointestinal (nausea, vomiting, diarrhea, constipation), dose-related, mostly mild to moderate, and concentrated during dose escalation; using a lower starting dose partially mitigated them. A mechanistically important signal is a dose-dependent increase in heart rate, which in the Phase 2 obesity trial peaked around 24 weeks before declining; glucagon receptor agonism also raises hepatic glucose output, requiring monitoring. Phase 3 topline data showed dose-dependent discontinuation due to adverse events. Because retatrutide is investigational, its long-term safety, cardiovascular outcomes, and effects in broad real-world populations are not yet established. Compounded, "research-use-only," or gray-market retatrutide is not quality-controlled and carries additional, unquantified risks.

Across the obesity trials, AOD-9604 was generally reported as well tolerated with a clean short-term safety signal, which is part of why it was later nominated for compounding review; however, these data come from time-limited studies and do not establish long-term safety. There is no established safety profile for chronic use, for injectable research-grade ("gray market") product, or for the unindicated cosmetic, joint, and anti-aging uses now marketed online. Purity, identity, and contamination of non-pharmaceutical material are real concerns, underscored by published forensic identification of illicit AOD9604 preparations (Drug Testing and Analysis, 2014; PMID 24976118). No dosing or administration guidance is provided here.

As of mid-2026 retatrutide is investigational and not approved by the FDA, EMA, MHRA, or any other regulator for any indication; it remains in Phase 3 development (the TRIUMPH program) by Eli Lilly. It is not a dietary supplement and any product sold as "research-use-only" retatrutide is unapproved.

AOD-9604 is not approved by the FDA (or any major regulator) for any therapeutic use; its obesity development program was discontinued, and it remains investigational/research-use-only. The FDA has evaluated it among nominated bulk drug substances for pharmacy compounding under section 503A and has flagged peptide candidates of this type as raising significant safety questions; it is also prohibited in sport and tested for by anti-doping authorities under the WADA framework.