What is identical
- The molecule. Tirzepatide, a dual GIP and GLP-1 receptor agonist, in both.
- The strengths. 2.5, 5, 7.5, 10, 12.5 and 15 mg.
- The ladder. Start at 2.5 mg, four weeks minimum per step, 2.5 mg increments.
- The device. The same KwikPen, four doses of 0.6 ml, 60 clicks per dose, and the same single-dose pen and vial formats where those are sold.
- The in-use window. Thirty days from first injection on the KwikPen.
- The pharmacokinetics. A half-life of about five days, steady state in roughly four weeks, and the same weekly trough.
Nothing on that list is approximately the same. It is the same product, filled and finished the same way.
What actually differs
| Mounjaro | Zepbound | |
|---|---|---|
| Active ingredient | Tirzepatide | Tirzepatide |
| Primary licensed use | Type 2 diabetes, plus weight management in several markets | Weight management, and obstructive sleep apnoea in obesity, in the United States |
| Where it is sold | Most markets worldwide, including the EU and the UK | United States |
| Device | KwikPen, single-dose pen, vials in some markets | KwikPen, single-dose pen, vials for self-pay |
| Ladder | 2.5 to 15 mg | 2.5 to 15 mg |
| Typical route to it | Diabetes or weight indication depending on market | Weight or sleep apnoea indication |
Licensing changes as regulators act. Your prescriber and your pharmacist know what is currently approved and stocked where you are.
In practice, if you are outside the United States you will be dispensed Mounjaro whatever you are being treated for. If you are inside it, the brand you receive follows the indication you were prescribed against.
Why one drug carries two names
A medicine is licensed for an indication, not simply approved as a substance. A manufacturer that wants a second indication runs separate trials and files a separate application, and it is common for the result to be marketed under a distinct name so that prescribing, labelling and reimbursement stay unambiguous.
Semaglutide does the same thing: Ozempic at diabetes doses, Wegovy at the weight-management dose, Rybelsus as the oral tablet. Liraglutide is Victoza and Saxenda. It is a labelling convention, not a formulation difference.
Where the difference has real consequences
Nothing about the pharmacology changes, and four practical things do.
Cost and coverage
The two brands are priced and reimbursed separately, and an insurer that covers one may decline the other for the same patient. This is the single most common reason people are moved between them.
Supply
Shortages have hit the two labels at different times. Being able to receive whichever is stocked is useful, and it means your history will show a brand change that is not a drug change.
Paperwork
Prior authorisation, employer plan exclusions and step therapy attach to the indication and therefore to the brand. The clinical facts are identical; the forms are not.
Travel
A prescription for one brand may not match the product available where you are travelling. Carrying documentation that names the active ingredient, not only the brand, avoids a slow conversation.
Switching between the two labels
Because the molecule and the doses are identical, moving from one brand to the other at the same milligram strength is a continuation, not a restart. No re-titration is implied by the brand change alone. Your prescriber may still adjust the dose for unrelated reasons, but the change of name is not one of them.
That is worth being deliberate about in your record. If a log treats the brand change as a new medication, your level curve breaks, the average dose statistics restart, and comparing this quarter with last becomes impossible for no clinical reason. In Penwise, tirzepatide is tirzepatide: the brand is recorded, the estimated level runs continuously across the change, and the pens are handled correctly on both sides.
The KwikPen generations, which apply to both
One device detail is worth knowing whichever label you hold. The original KwikPen finishes with a measurable amount of liquid left after its four labelled doses. Lilly began shipping a redesigned device in April 2026 that is built to finish essentially empty.
Both generations are in circulation under both brand names, and the carton does not make it obvious. Any supply arithmetic that assumes the wrong one is wrong, which is why Penwise asks rather than guessing. Using leftover volume as a dose is off-label and manufacturers advise against it; the reason to know which device you hold is that the remaining-supply count is otherwise incorrect.
What to record either way
- The active ingredient, not just the brand. It is the field that stays true across a label change, a market change and a shortage.
- The strength and the date of every increase. The ladder is identical, so this is the number that governs your level and your side-effect windows.
- Which device you are using. KwikPen, single-dose pen or vial changes the supply maths, and so does which KwikPen generation.
- The brand on the box. Not for pharmacology, for the pharmacy and insurance conversation later.
- First-use dates. The 30-day in-use window is tight enough that two shifted shots can push the fourth dose past it. See how long a pen lasts.
If you are comparing tirzepatide with the other weekly option rather than with itself, Mounjaro vs Ozempic and Mounjaro vs Wegovy are the pages for that. For dosing mechanics, the full titration ladders cover both labels identically, and the Zepbound tracker and Mounjaro tracker pages cover the app side.
One drug, one history, whatever the box says
Tirzepatide tracked continuously across a brand change, with the right pen and the right level curve. Free core tracker, no account.
Common questions
Is Zepbound the same as Mounjaro?
Why are there two names for tirzepatide?
Do I need to re-titrate when switching between Zepbound and Mounjaro?
Can I get Zepbound outside the United States?
Is one of them stronger than the other?
How should I log a brand change in a tracker?
Sources
Every factual claim on this page traces to the product information a regulator publishes, or to a published trial. Links open on the site of whoever issued the document.
- Zepbound (tirzepatide) prescribing information DailyMed, U.S. National Library of Medicine
- Mounjaro: EPAR product information European Medicines Agency
- Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1) New England Journal of Medicine, 2022
Penwise is a tracking and education tool, not a medical device. Nothing on this page is medical advice, a diagnosis or a recommendation to start, stop or change a dose. Dosing decisions belong to you and your clinician. Ozempic, Wegovy, Rybelsus, Saxenda and Victoza are trademarks of Novo Nordisk; Mounjaro, Zepbound and Trulicity are trademarks of Eli Lilly. Penwise is not affiliated with, endorsed by or connected to either company.