The GIP arm: the second incretin
For years GIP, the other incretin hormone, was treated as a dead end for metabolic drugs. Then tirzepatide paired it wi…
The forgotten incretin that turned out to matter
For years GIP, the other incretin hormone, was treated as a dead end for metabolic drugs. Then tirzepatide paired it with GLP-1 and outperformed GLP-1 alone, and GIP suddenly looked essential. Retatrutide keeps that GIP arm and adds glucagon on top, so understanding what GIP contributes is key to understanding why two receptors beat one.
This unit covers GIP biology, why its role was underrated, and the still-live scientific debate about whether you should activate or block the GIP receptor. That debate is genuinely unresolved, and it is a good example of how this field advances faster than its textbooks.
Key terms
The incretin nobody wanted
GIP was actually the first incretin discovered, yet for decades it was sidelined: in type 2 diabetes its insulin effect looked blunted, so drug developers chased GLP-1 instead. The story changed only when GIP was combined with GLP-1 and the pair beat GLP-1 alone, a reversal worth appreciating before the biology.
The lesson is that a target dismissed in isolation can shine in combination. Retatrutide inherits the GIP arm precisely because the dual-agonist data made it credible, then asks whether adding a third receptor pushes further still.
AdvancedWhy GIP looked broken in diabetes
In type 2 diabetes the pancreas response to GIP appears blunted, which is what made GIP look like a dead end on its own. Part of the revival came from the observation that improving glucose control can partly restore GIP responsiveness, so pairing it with a strong GLP-1 effect lets the once-doubted arm pull its weight again.