Is Retatrutide a "GLP-3" Drug? Not Exactly

Scroll through enough discussion of retatrutide and you’ll eventually see it called a “GLP-3” drug, usually framed as the logical next step after GLP-1 (semaglutide) and dual-target GLP-1/GIP compounds (tirzepatide). It’s a catchy way to describe the progression, and the underlying idea, that retatrutide adds another target on top of the others, is correct. The name itself isn’t. There’s no naturally occurring hormone called GLP-3.

What retatrutide actually adds

As covered in our GLP-1 compounds comparison, retatrutide is a triple hormone receptor agonist targeting GLP-1, GIP, and glucagon. That third target is a real, well-established hormone receptor: it’s just not part of the “GLP” family. Glucagon is the hormone your body releases to raise blood sugar (roughly insulin’s opposite number), and it’s thought to contribute an effect on energy expenditure that the other two targets don’t produce on their own.

So the “one more receptor than tirzepatide” framing is accurate. Calling that third receptor “GLP-3,” as if it were a newly discovered hormone in the same family as GLP-1 and GLP-2, isn’t: it’s a nickname that took hold because it fits the pattern, not because it’s the compound’s actual mechanism.

Why the nickname stuck anyway

Part of it is genuinely just convenient shorthand: “GLP-1, GLP-2, GLP-3” reads as a clean progression, even though GLP-2 (a real hormone involved in gut-lining growth, covered separately here) isn’t part of this progression either. Part of it is likely marketing-driven, since “the next GLP” is an easy story to tell about a newer, more powerful compound. Either way, it’s worth knowing the difference between the shorthand people use in conversation and what’s actually in the vial.

The accurate version

Retatrutide = GLP-1 + GIP + glucagon receptor agonism, not a mysterious third GLP hormone. If you’re comparing it against semaglutide and tirzepatide, the GLP-1 compounds comparison breaks down all three, plus cagrilintide, side by side.