Tirzepatide is usually introduced as "a GLP-1 drug that also does something else". That description is backwards, and the correct version explains most of what is distinctive about it.
What it is
A 39-amino-acid peptide built on the backbone of GIP — glucose-dependent insulinotropic polypeptide, a gut hormone released after eating, distinct from GLP-1. Engineering added activity at the GLP-1 receptor. So it is a GIP analogue with GLP-1 action, not a GLP-1 analogue with a bonus.
Like semaglutide it carries a fatty-acid chain that binds it to albumin in the blood, which is why a peptide that would otherwise be cleared within minutes can be injected once a week.
Whether occupying two receptors is better than one is a question about outcomes, not about the molecule, and it is currently being tested head-to-head against both a single-receptor drug and a triple-receptor one — the triple agonist retatrutide, which adds glucagon to the same idea.
Two approvals, one dose scale
| Product | Approved | For | The label's dose scale |
|---|---|---|---|
| MOUNJARO | 2022-05-13 | Type 2 diabetes | 2.5 mg → 5 mg → +2.5 mg steps → max 15 mg weekly |
| ZEPBOUND | 2023-11-08 | Weight management; obstructive sleep apnoea in obesity | Same escalation; maintenance 5, 10 or 15 mg weekly |
Every figure is read from current FDA labelling on 2026-09-08 and records what the label states.
The important structural difference from semaglutide is that here the numbers mean the same thing on both labels. One molecule, one escalation, two sets of indications. A patient moving between the two products is not moving between dose scales.
Two details the summaries usually drop. The MOUNJARO label sets a lower ceiling for children aged 10 and over — 10 mg weekly against the adult 15 mg. And the 2.5 mg first step is a tolerability step rather than a treatment dose: both labels move off it after four weeks, and ZEPBOUND's stated maintenance range starts at 5 mg.
The indication nobody mentions
ZEPBOUND is approved for moderate-to-severe obstructive sleep apnoea in adults with obesity, and the label gives that indication its own maintenance range: 10 mg or 15 mg once weekly, rather than the 5-to-15 mg used for weight reduction.
It is a real, separate approval with its own dose band, and it is almost entirely absent from consumer coverage of the drug — which is worth noting because it is the kind of thing a label check finds in a minute and a summary of a summary never will.
No approved oral form
Semaglutide has approved tablets and an absorption enhancer to make them work. Tirzepatide has neither. Every approved presentation is a weekly subcutaneous injection, which means any product presented as oral tirzepatide sits outside all approved labelling.
That constraint is a consequence of being a peptide, and it is the reason a non-peptide GLP-1 tablet is being developed at all: a small molecule is not digested the way a chain of amino acids is, so it needs neither an enhancer nor an injection. A separate naming confusion belongs here too — a drug engaging two receptors is often mistaken for the second rung of a numbered series, and the hormone people call GLP-3 does not exist in humans.
What this entry does not cover
Cost, comparative weight-loss outcomes against other drugs, and what happens on stopping are treatment questions rather than questions about the compound.
On the research-chemical market, the same statement applies as for every approved drug in this library: a vial sold under this name is not MOUNJARO or ZEPBOUND, and none of the checks behind those labels apply to it.
Tirzepatide is also the backbone of the newest muscle-preservation trials: Eli Lilly is testing it alongside bimagrumab, an activin-receptor antibody, including as a single co-formulated product.
Sources
- FDA labelling for MOUNJARO (NDA 215866) and ZEPBOUND (NDA 217806), retrieved through openFDA on 2026-09-08; dosage and administration sections quoted directly.
- Drugs@FDA original approval records: NDA 215866 approved 2022-05-13; NDA 217806 approved 2023-11-08.