Mounjaro and Zepbound are not two drugs. They are one molecule, tirzepatide, made by one manufacturer, Eli Lilly, sold in the same six strengths, and approved twice. The comparison people are searching for does not exist at the level of the chemistry. It exists at the level of the paperwork, and the paperwork turns out to say more than most comparisons do.
Every figure below was read on 23 September 2026 from the two manufacturer labels: MOUNJARO (NDA 215866, Lilly's version effective 27 August 2026, via DailyMed) and ZEPBOUND (NDA 217806, effective 28 August 2026, via openFDA). Nothing here is a dose or a schedule; our titration schedules page reports what the labels say about dosing, and our editorial standards explain why that sits on one page only.
One molecule, two applications
| Mounjaro | Zepbound | |
|---|---|---|
| Molecule | tirzepatide | tirzepatide |
| FDA application | NDA 215866 | NDA 217806 |
| Approved for | Blood-sugar control in type 2 diabetes; heart-risk reduction in type 2 diabetes at high cardiovascular risk | Long-term weight reduction; obstructive sleep apnoea with obesity |
| Ages | Adults, and children 10 and older | Adults only |
| Strengths | 2.5, 5, 7.5, 10, 12.5, 15 mg | 2.5, 5, 7.5, 10, 12.5, 15 mg |
| Forms | Single-dose pen or vial; multi-dose vial; KwikPen | Single-dose pen or vial; multi-dose vial; KwikPen |
| Warning against other tirzepatide products | Not stated | Stated as a Limitation of Use |
The strength tables in section 3 of the two labels are identical line for line, down to the multi-dose vial concentrations of 4.17 mg/mL to 25 mg/mL. Nothing in the product itself tells the two brands apart. What tells them apart is what each was proved to do, and in whom.
This is the same structure as Wegovy and Ozempic, which are one semaglutide under four applications. Lilly's version is simpler — two applications, both injections — but the rule is the same: the brand follows the diagnosis.
The line is the disease, and the paediatric line runs the other way
Mounjaro is the diabetes brand — and, on its current label, also a heart-risk brand: it is indicated to reduce major cardiovascular events in adults with type 2 diabetes at high risk of them. Zepbound is the weight and sleep-apnoea brand. That much is widely known.
Less widely known: on the current label, Mounjaro is the only tirzepatide brand approved for anyone under 18. Its indication now reads "adults and pediatric patients 10 years of age and older with type 2 diabetes mellitus", and section 6 reports a paediatric trial of 97 patients with a mean age of 15. Zepbound has no paediatric indication for either of its uses. So the brand most people think of as the "weight-loss" one is the one restricted to adults, and the "diabetes" one is the one that reaches children — for diabetes only.
The sleep-apnoea approval is Zepbound's alone. Our sleep apnoea page covers the two trials behind it.
The side-effect gap nobody explains
This is the finding worth having. At the same doses of the same molecule, the two labels print very different side-effect rates.
| Reaction | Mounjaro placebo | Mounjaro 5 / 10 / 15 mg | Zepbound placebo | Zepbound 5 / 10 / 15 mg |
|---|---|---|---|---|
| Nausea | 4% | 12 / 15 / 18% | 8% | 25 / 29 / 28% |
| Diarrhoea | 9% | 12 / 13 / 17% | 8% | 19 / 21 / 23% |
| Vomiting | 2% | 5 / 5 / 9% | 2% | 8 / 11 / 13% |
| Constipation | 1% | 6 / 6 / 7% | 5% | 17 / 14 / 11% |
| Any gastrointestinal reaction | 20.4% | 37.1 / 39.6 / 43.6% | 30% | 56 / 56 / 56% |
| Stopped because of a GI reaction | 0.4% | 3.0 / 5.4 / 6.6% | 0.5% | 1.9 / 3.3 / 4.3% |
Mounjaro figures from its Table 1 and GI text (pool of SURPASS-1 and SURPASS-5); Zepbound figures from its Table 1 and GI text (pool of Studies 1 and 2).
Three things are visible here that neither label says.
Nausea on Zepbound runs at roughly twice the Mounjaro rate at every dose. The gap also holds after subtracting each label's own placebo: nausea attributable to the drug is 8 to 14 percentage points on Mounjaro and 17 to 21 on Zepbound.
And yet more people stopped Mounjaro because of stomach side effects, not fewer. At 15 mg, 6.6% of Mounjaro patients discontinued for a gastrointestinal reaction against 4.3% on Zepbound. The label that reports less nausea reports more quitting over it.
The populations explain more than the molecule can. Mounjaro's pooled trials enrolled people with a mean age of 58 who had had diabetes for an average of 9.1 years, 54% of them men, and one of the two trials added tirzepatide to basal insulin. Zepbound's enrolled people with a mean age of 47, 63% of them women, three-quarters without diabetes. Age, sex, background medicines and years of illness all plausibly change how nausea is experienced and reported. Both labels carry the standard sentence that rates from one programme "cannot be directly compared" with another's — and here the two programmes belong to the same molecule, which makes the warning unusually concrete.
The practical reading: a person moving between the two brands is not moving between two side-effect profiles. They are moving between two descriptions of one, written from two different groups of people. Our Zepbound side effects page sets out that label's full record.
Weight: the diabetes discount is inside Zepbound's own label
Mounjaro is not approved for weight loss, and its trials measured weight as a secondary result in kilograms over 40 weeks. Zepbound's measured it as the primary result in percent over 72. Placing those side by side would compare two different clocks.
Zepbound's label, though, contains its own diabetes comparison. Study 2 (SURMOUNT-2, NCT04657003) enrolled 938 adults with type 2 diabetes; Study 1 (SURMOUNT-1, NCT04184622) enrolled 2,539 without it. Same drug, same 72 weeks, same lifestyle programme.
| 72 weeks, intention-to-treat | Placebo | 10 mg | 15 mg |
|---|---|---|---|
| Without diabetes (Study 1) | −3.1% | −19.5% | −20.9% |
| With type 2 diabetes (Study 2) | −3.2% | −12.8% | −14.7% |
| Share losing ≥20%, without diabetes | 3.1% | 50.1% | 56.7% |
| Share losing ≥20%, with diabetes | 1.0% | 21.5% | 30.8% |
At 15 mg, people with diabetes lost about 30% less of their body weight than people without it — 14.7% against 20.9% — and were roughly half as likely to reach a 20% loss. The placebo arms are almost identical, so the difference is in how the drug behaved, not in the background.
That is the population Mounjaro is approved for. Its own trials report a 7.8 kg loss at 15 mg as monotherapy over 40 weeks (SURPASS-1) and 11.2 kg as an add-on to metformin, where semaglutide 1 mg gave 5.7 kg (SURPASS-2). Anyone reading headline tirzepatide weight-loss figures from the non-diabetic trial as a prediction for a person with type 2 diabetes is reading the wrong row. Our tirzepatide review and the tirzepatide against semaglutide comparison carry the trial record in full.
One warning, printed once
Zepbound's indications section ends with a Limitation of Use: "Coadministration with other tirzepatide-containing products or with any glucagon-like peptide-1 (GLP-1) receptor agonist is not recommended." Lilly's current Mounjaro label, read on the same day, contains no such sentence; the phrase "tirzepatide-containing" does not occur in it.
The pharmacology is symmetrical. Tirzepatide is tirzepatide. Someone holding both prescriptions, or taking a compounded product alongside either brand, is doubling one molecule whichever document they read. But only one of the two documents says so — the same asymmetry we found between Wegovy's and Ozempic's labels, where the weight-management brand carries the warning and the diabetes brand does not. Twice now, across two manufacturers, the warning about the same molecule under another name sits on only one side of the pair.
Price follows the brand, not the molecule
Lilly publishes self-pay prices for Zepbound. For Mounjaro, what it publishes is a savings card, and the card's terms reveal the underlying price. Read from Lilly's own pages in September 2026:
- Mounjaro: the savings card for people whose insurance does not cover it sets a $499 monthly price with a stated maximum saving of $647, which puts the underlying price at $1,146 for a 28-day fill. Arithmetic and terms on our Mounjaro cost page.
- Zepbound: the KwikPen self-pay price runs $299 at 2.5 mg to $699 at 10 mg and above, with a $449 purchase offer on the higher strengths that lapses if a refill is more than 45 days late. Full terms on our Zepbound cost page.
Insurance often runs the other way, because plans and Medicare Part D distinguish between drugs used for diabetes and drugs used for weight loss. The same tirzepatide can be covered as Mounjaro and excluded as Zepbound for the same person; the statute behind that is on our insurance coverage page.
Switching between them
Neither label contains a section on switching from one brand to the other, and neither lists the other by name. Because the strengths are identical, the question people ask — "is 5 mg of one the same as 5 mg of the other?" — has a factual answer at the level of the molecule and strength: the labels describe the same drug at the same amount per injection. Whether a switch is appropriate for a person, and at what point in their treatment, is a prescribing decision the labels leave to the prescriber, and so do we.
What this page cannot tell you
- Which brand suits a particular person. That follows from their diagnosis, coverage and history, and it is a conversation with a prescriber.
- Why the nausea rates differ. The population differences are documented; the cause is not. No trial has randomised people with the same characteristics to the two brands, and none will, because they are the same drug.
- Anything newer than 23 September 2026. Both labels are revised several times a year, and Mounjaro's paediatric indication is itself a recent addition.
Sources
- MOUNJARO (tirzepatide) prescribing information, Eli Lilly and Company, NDA 215866, SPL version 40 effective 2026-08-27 — read 2026-09-23 on DailyMed: sections 1, 3, 6.1 and 14. openFDA's brand-name search returns only repackagers' copies of this label; the figures quoted here match between them, and the Limitation of Use is absent from both.
- ZEPBOUND (tirzepatide) prescribing information, Eli Lilly and Company, NDA 217806, SPL effective 2026-08-28 — read 2026-09-23 via openFDA: sections 1, 3, 6.1 and 14.1.
- SURMOUNT-1, NCT04184622, and SURMOUNT-2, NCT04657003, as reported in the Zepbound label's Table 2.
- Lilly savings and self-pay terms for Mounjaro and Zepbound, as read and dated on our cost pages (September 2026).