What Is GLP-3? There Is No Such Hormone — Here's What People Mean

There is no such thing as GLP-3. No hormone, no receptor, and no approved drug by that name — a full-label search of FDA's DailyMed for “GLP-3” on August 19, 2026 returned zero results. What people mean when they say it is retatrutide, an investigational Eli Lilly molecule that activates three receptors at once. The “3” counts receptors, not generations of a hormone. That distinction matters more than it sounds, because the term has become the label under which unapproved retatrutide is sold online as “GLP-3 peptide,” “GLP-3 RT,” and “GLP-3 R.” The same confusion is starting around cagrilintide and petrelintide, which are amylin analogs rather than GLP-1s at all.

The short answer

What retatrutide actually is

Retatrutide (Lilly designation LY3437943) is a 39-amino-acid single peptide engineered from a GIP backbone, with a fatty di-acid chain attached so it binds albumin and lasts long enough for weekly dosing ^[1]. It is described in the peer-reviewed literature as “the first GLP-1/GIP/GCG triple agonist to complete phase 2 trials, with phase 3 studies ongoing” ^[1]. GCG is glucagon.

• GLP-1 receptor — the appetite and satiety arm, the same one semaglutide works through.
• GIP receptor — the second arm tirzepatide added on top of GLP-1.
• Glucagon receptor — the third arm, unique to retatrutide in this class. It raises energy expenditure and reduces liver fat, and it is the reason the effect size is larger than tirzepatide's.

So “triple” is accurate and “GLP-3” is not: two of the three receptors it hits are not GLP receptors at all. For the trial data behind it, see our retatrutide triple agonist evidence review, and for how it compares head-to-head, retatrutide vs tirzepatide.

You cannot get it from a pharmacy

Retatrutide is investigational. As of August 19, 2026 ClinicalTrials.gov listed 32 registered retatrutide studies, with phase 3 work still active ^[3]. No FDA-approved retatrutide product exists, which means there is no prescription version, no pharmacy price, and no approved dose.

That is the gap the “GLP-3” label fills commercially. Search results for these terms are heavily populated by vendors selling vials described as “GLP-3 peptide,” “GLP-3 R,” or “GLP-3 RT” — the “R” and “RT” being seller shorthand for retatrutide. These are not prescriptions being filled. They are unapproved material sold outside the drug-approval system, frequently labeled “research use only,” and we cover why that boundary matters in our retatrutide regulatory status and sourcing guide.

Why the nickname stuck

It is a useful shorthand and a bad description. “The next one after tirzepatide” is genuinely hard to say quickly, and “GLP-3” sounds like a version number in a product line people already understand. Mainstream outlets have started addressing the term directly rather than using it, and Lilly itself does not market retatrutide under that name. If you are reading a page that uses “GLP-3” as though it were a drug class rather than a nickname, that is a reasonable signal to check what else on the page is imprecise.