After a meal, the gut sends hormone signals that shape insulin release and fullness. Tirzepatide activates the receptors for two of them, and in Australia the same molecule is a registered prescription medicine.
Tirzepatide · Dual incretin receptor peptide
Incretins are hormones released by the gut when food arrives. They tell the pancreas to release insulin, slow the stomach and contribute to the feeling of fullness that helps bring a meal to an end. The two best studied are GLP-1 and GIP. Tirzepatide was built to activate both receptors with one molecule, and the evidence is from large human trials in adults with type 2 diabetes or obesity.
Tirzepatide, development code LY3298176, is a synthetic 39-amino-acid peptide based on the GIP sequence and modified so that it also activates the GLP-1 receptor. Both are receptors for incretins: GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide) are released from the gut after eating and prompt insulin release in a glucose-dependent way. GLP-1 also slows stomach emptying and acts on appetite centres in the brain; GIP acts on fat tissue as well as the pancreas. A fatty-acid side chain binds albumin in the blood and slows clearance, giving a half-life of about five days.
In receptor studies tirzepatide engages the GIP receptor more strongly than the GLP-1 receptor and signals differently from native GLP-1 at that receptor, which its developers describe as an imbalanced and biased agonist. Whether that profile explains its clinical results is still being examined.
The clinical programme is large. SURPASS-2 compared tirzepatide with semaglutide 1 mg over 40 weeks in 1,879 adults with type 2 diabetes and measured HbA1c, a three-month average of blood glucose (Frias et al., 2021). SURMOUNT-1 was a 72-week placebo-controlled trial in 2,539 adults with obesity or overweight but without diabetes, measuring body weight; weight reduction was substantially greater than placebo at all three doses, with gastrointestinal side effects the most common reason for stopping (Jastreboff et al., 2022). SURMOUNT-5 compared tirzepatide with semaglutide 2.4 mg head to head over 72 weeks in adults with obesity (Aronne et al., 2025).
Those results led to registration. In Australia, tirzepatide is entered on the Australian Register of Therapeutic Goods as Mounjaro (sponsor Eli Lilly Australia), a prescription-only medicine (ARTG 379330). In the United States it is approved as Mounjaro for type 2 diabetes and as Zepbound for chronic weight management in adults with obesity, or overweight with a weight-related condition (FDA, 2023). The medicine is a manufactured, sterile, dose-controlled product used under prescription; the research material on this page is not that product.
The trials used the pharmaceutical formulation, with dose escalation and medical monitoring, in adults who met specific entry criteria. Results in other populations, and after treatment stops, are less well described; weight regain after discontinuation was reported in the SURMOUNT-4 extension trial (Aronne et al., 2024). How much of the effect comes from GIP receptor activity, as opposed to GLP-1 activity alone, is a mechanistic question the large trials were not designed to answer.
Research-grade peptide has no established equivalence to the registered medicine in identity, purity, sterility or dose, so trial findings do not transfer to it.
Tirzepatide is registered in Australia as the prescription medicine Mounjaro (Eli Lilly Australia, ARTG 379330 and related entries); that registration applies to the manufactured medicine, not to research material. In the United States the FDA has approved it as Mounjaro for type 2 diabetes and as Zepbound for chronic weight management.
Sources and status checked 2026-09-22
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