Why Two Receptors Beat One

GLP-1 monoagonists (like semaglutide) target a single incretin receptor. Tirzepatide targets two — GIP and GLP-1 — on a single molecule engineered from the GIP backbone. The hypothesis is that GIP activation synergizes with GLP-1 receptor activation to allow greater weight reduction than GLP-1 alone.

This is borne out in trials: in SURMOUNT-5 (the first head-to-head), tirzepatide produced −20.2% weight loss vs −13.7% for semaglutide 2.4 mg over 72 weeks. The dual-agonism concept — and tirzepatide's biased signaling profile (low β-arrestin recruitment) — is the core of this thread.