GLP-1

GLP-1 (short for glucagon-like peptide-1) is a hormone your gut releases when you eat. It’s a peptide, and it does several jobs at once, all pointed at handling a meal: it tells the pancreas to release insulin when blood sugar rises, it dials down appetite through signals to the brain, and it slows how fast the stomach empties so you feel full longer.

The catch with natural GLP-1 is that the body destroys it within a couple of minutes — far too quick to be useful as a medicine on its own. So drugmakers built longer-lasting analogs of it. Semaglutide (Ozempic, Wegovy) and the GLP-1 side of tirzepatide (Mounjaro, Zepbound) are engineered copies of this hormone that survive for days, letting a single injection carry the signal for a week.

A concrete example is the difference between semaglutide and tirzepatide. Semaglutide acts as a longer-lasting agonist at the GLP-1 receptor, extending one meal-related signal into a medicine designed for once-weekly use. Tirzepatide activates that same receptor but also activates the receptor for GIP, the other main incretin hormone, so GLP-1 describes only one side of its design. Put simply, semaglutide shows a drug built around the GLP-1 signal alone, while tirzepatide shows how that signal can be combined with a second pathway in one compound rather than relying entirely on the GLP-1 pathway by itself.

That’s the entire mechanism behind the weight-loss and diabetes drugs dominating headlines: they don’t do anything exotic, they just keep pressing GLP-1’s own buttons — more insulin when it’s needed, less appetite, slower digestion — for far longer than the real hormone ever could.

GLP-1 is also one of the two main incretins, the family of gut hormones that cue insulin after eating. Understanding GLP-1 is basically the key that unlocks how this whole class of drugs works.