AOD-9604 vs. Retatrutide: two mechanisms, one research goal of fat loss

In obesity research over the past two years, a single molecule has dominated the headlines: Retatrutide. Phase 2 data with up to 24% body weight loss and Phase 3 announcements from TRIUMPH-4 have placed the triple agonist at the centre of attention. Alongside it, a much smaller molecule that takes a completely different route has existed since the early 2000s: AOD-9604, a synthetic fragment of human growth hormone.

Both peptides are studied in preclinical research in the context of "fat loss", yet they intervene at entirely different points in the biological system. A clean comparison of the mechanisms is therefore relevant for any study design that wants to address the lipid axis.

Mechanism of AOD-9604: targeted lipolysis via the adipocyte

AOD-9604 (Anti-Obesity Drug 9604, also hGH fragment 176-191) is a 16-amino-acid peptide that reproduces the C-terminal region of human growth hormone. The underlying hypothesis from the original work by Ng and Bornstein (Monash University, 1990s): the lipolytic effect of full-length hGH is mediated primarily by this short C-terminal sequence, while the growth-promoting and blood-glucose effects run through other regions of the molecule.

In preclinical models, AOD-9604 acts as follows:

• Activation of beta-3-adrenergic receptors on adipocytes
• Downstream reaction: hormone-sensitive lipase (HSL) is upregulated
• Result: stored triglycerides are cleaved into free fatty acids and glycerol and mobilised for energy utilisation
• In parallel: inhibition of lipogenesis (new formation of fat cells)

AOD-9604metabolic

Modified hGH fragment (176-191) studied for fat metabolism and lipolysis research. Interacts with beta-3 adrenergic receptors without growth-promoting effects.

Mechanism of Retatrutide: systemic triple agonism

Retatrutide (LY3437943) was developed by Eli Lilly as the next generation of incretin-based anti-obesity agents. In contrast to Semaglutide (GLP-1 mono agonist) and Tirzepatide (GLP-1/GIP dual agonist), Retatrutide simultaneously activates three receptors:

• GLP-1 receptor: appetite reduction, delayed gastric emptying, glucose-dependent insulin secretion
• GIP receptor: additional insulin action, further modulation of energy homeostasis
• Glucagon receptor: increased energy expenditure, enhanced lipolysis via the liver, promotion of fatty acid oxidation metabolism

In the Phase 2 NEJM publication (Jastreboff et al., 2023), at the highest dose (12 mg/week) a placebo-adjusted weight loss of 24.2% was documented after 48 weeks (PubMed: https://pubmed.ncbi.nlm.nih.gov/37366315/). In December 2025, Eli Lilly reported topline data from TRIUMPH-4 showing up to 32 kg (71.2 lbs) of weight loss and significant pain reduction in osteoarthritis.

Retatrutidemetabolic

First-ever triple-action weight management peptide targeting three receptors at once: GIP, GLP-1, and glucagon. Shown exceptional results in Phase 2 trials - up to 24% weight reduction. The most advanced metabolic peptide available.

Comparison: AOD-9604 vs. Retatrutide at a glance

Criterion	AOD-9604	Retatrutide
Class	hGH fragment (176-191)	GLP-1/GIP/glucagon triple agonist
Size	16 amino acids, ~1.8 kDa	39 amino acids, fatty-acid modified
Primary site of action	Adipocyte (β3/HSL)	Pancreas, hypothalamus, stomach, liver
Breadth of action	selectively lipolytic	systemically metabolic
Appetite effect	none	strongly reducing
IGF-1 rise	not relevant	not relevant
Glucose influence	minimal	direct (incretin-mediated)
Half-life	short (minutes)	long (~6 days, weekly dosing in studies)
Clinical phase	programme discontinued in 2007	Phase 3 ongoing

Research combination: simultaneous or sequential?

In the grey literature and on research platforms, the question regularly arises whether AOD-9604 and Retatrutide can be investigated in parallel in stack designs. Mechanistically, the two pathways scarcely overlap: AOD-9604 mobilises locally stored fatty acids at the adipocyte, Retatrutide reduces caloric intake via central appetite mechanisms and increases overall energy expenditure centrally. In models that aim to measure fat loss independently of behaviour, both effects could be isolated separately.

For studies that want to model exclusively fat metabolism without the broad incretin intervention, AOD-9604 is the mechanistically clean tool. For studies that want to capture the full metabolic picture, Retatrutide remains the substance with the currently most extensive Phase 2/3 dataset.

Sourcing and quality assurance

Both peptides are supplied by Peptides Direct as lyophilised powder. Every batch is independently tested by Janoshik Analytical via HPLC for identity and purity (≥98%). The certificate of analysis (CoA) is openly accessible on the respective product page, batch-specific, and contains purity, measurement date, and batch number for full traceability.

For reconstitution, bacteriostatic water (USP grade) is recommended, which can also be obtained from the shop.

Sources

• Jastreboff AM et al. Retatrutide, a Triple-Hormone Receptor Agonist, for Obesity - A Phase 2 Trial. NEJM, 2023. PubMed: https://pubmed.ncbi.nlm.nih.gov/37366315/
• Eli Lilly. TRIUMPH-4 topline results, December 2025: https://www.lilly.com/news/stories/what-to-know-about-retatrutide
• Ng FM, Bornstein J. Hyperglycemic action of synthetic C-terminal fragments of human growth hormone. Am J Physiol, 1978/follow-up work in the 1990s on the lipolysis specificity of fragment 176-191.
• Heffernan M et al. The effects of human GH and its lipolytic fragment (AOD9604) on lipid metabolism following chronic treatment in obese mice and beta3-AR knock-out mice. Endocrinology, 2001.

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This article is intended for information purposes for scientific research only.

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