GIP receptor

GIP stands for glucose-dependent insulinotropic polypeptide. Like GLP-1, it is an incretin — a hormone your gut releases after a meal that tells the pancreas to respond. Unlike GLP-1, it had no weight-loss drug built around it until tirzepatide arrived with both receptors in its sights.

Tirzepatide is described on its label as a GIP receptor and GLP-1 receptor agonist that selectively binds and activates both targets. The label is candid about how much is still unknown: nonclinical studies suggest the addition of GIP may further contribute to the regulation of food intake, and both GIP and GLP-1 receptors are found in brain areas involved in appetite regulation. That is a mechanistic hypothesis, not a settled account.

What is not in doubt is the clinical arithmetic. In SURMOUNT-5, 751 adults with obesity were randomized to tirzepatide or semaglutide for 72 weeks; average weight change was −20.2% versus −13.7%. In type 2 diabetes, SURPASS-2 found tirzepatide superior to semaglutide on A1C at all three doses tested. Whether that advantage comes from GIP itself, from the molecule’s overall receptor engagement, or from dose intensity is still being argued in the literature.

The confusion worth flagging: GIP is not simply “a second GLP-1.” For years researchers thought blocking GIP, not activating it, would help with weight — and drugs taking the opposite approach are still in trials. Both can plausibly work, which tells you the biology is more tangled than a one-line explanation allows.

Questions for a clinician: whether the extra receptor matters for your specific situation or whether tolerability should drive the choice; and what happens if you cannot reach a high tirzepatide dose, since the SURMOUNT-5 advantage was measured at maintenance doses, not starter ones. Our SURMOUNT-5 analysis and the tirzepatide drug page cover the detail.