Is tirzepatide the same as Mounjaro?

The active ingredient

The Mounjaro® label describes tirzepatide as a once-weekly agonist of two receptors, GIP and GLP-1. It is built on the sequence of the gut hormone GIP, with aminoisobutyric acid at positions 2 and 13 and a 20-carbon fatty diacid attached at position 20 through a linker. Its molecular weight is 4813.53 daltons ^[1].

MedlinePlus, the drug guide of the US National Library of Medicine, files the medicine under its ingredient name, tirzepatide injection, and lists Mounjaro® and Zepbound® as its brand names ^[12]. The ingredient name describes the molecule; a brand name belongs to one approved product, with its own label, devices and instructions.

What is in each pen and vial

Each single-dose pen or vial holds 0.5 mL with tirzepatide, sodium chloride, sodium phosphate and water ^[1]. The multi-dose vial and the four-dose KwikPen® deliver 0.6 mL per dose and add benzyl alcohol, glycerin and phenol; the Canadian monograph names benzyl alcohol and phenol as preservatives ^[1][8]. The Zepbound® label gives exactly the same ingredients and amounts in its own section 11 ^[2].

That full description, including the inactive ingredients, is part of what the brand name stands for. The Canadian monographs go one step further and list benzyl alcohol among the ingredients that rule the medicine out for someone who is hypersensitive to it ^[7][8].

Two brands, one molecule

Lilly sells tirzepatide under two names. Mounjaro® is approved, with diet and exercise, to improve blood sugar control in type 2 diabetes, in adults and in children from age 10, and to lower the risk of major cardiovascular events in adults with type 2 diabetes at high risk. Zepbound® is approved, with a reduced-calorie diet and more activity, for weight reduction and long-term maintenance in adults, and for obstructive sleep apnea of moderate to severe degree in adults who also have obesity ^[1][2].

Both labels list the same strengths, 2.5 mg to 15 mg, in single-dose pens and vials, and four-dose multi-dose vials and KwikPens ^[1][2].

The FDA’s Drugs@FDA database shows how the two brands arrived. Mounjaro® (application NDA 215866) was approved on 13 May 2022 and classed as a new molecular entity; Zepbound® (NDA 217806) followed on 8 November 2023 ^[3][4]. Both labels open with the same line, "Initial U.S. Approval: 2022" ^[1][2]. When we searched Drugs@FDA on 20 October 2026, these two Lilly applications were the only tirzepatide entries.

Where the two labels differ

The Zepbound® label advises against combining it with any other product that contains tirzepatide, or with any GLP-1 receptor agonist, and that would include Mounjaro® ^[2]. Other differences in wording:

• Starting dose: both start at 2.5 mg weekly. The Zepbound® label describes 2.5 mg only as a way to begin, not as an approved dose to stay on ^[1][2].
• Increases: Mounjaro® ties each 2.5 mg step to whether more blood sugar control is needed; Zepbound® describes maintenance doses of 5, 10 or 15 mg chosen by response and tolerability ^[1][2].
• Age: Mounjaro® includes children 10 and older with type 2 diabetes, with a maximum of 10 mg for them; the Zepbound® label says safety and effectiveness in children have not been established ^[1][2].
• Half-life: about 5 days in the Mounjaro® label, and about 5 to 6 days in people with overweight or obesity in the Zepbound® label ^[1][2].
• Self-injection with the KwikPen®: the Mounjaro® label does not recommend it for children or for people with impaired vision unless the prescriber decides otherwise; the Zepbound® label names only impaired vision ^[1][2].
• Insulin: only the Mounjaro® label explains that tirzepatide and insulin are given as separate injections, never mixed, and not right next to each other ^[1].

Other countries, other names

The two-name split is not the same everywhere. The European Union has a single tirzepatide product, Mounjaro®, authorised on 15 September 2022 ^[5]. Canada has two names, as the US does, but with different presentations. The table sets out the documents checked on 20 October 2026.

Which name is on your box depends on where it was dispensed, and the leaflet in your own pack is the version that applies to you.

Compounded tirzepatide is neither

The FDA states that compounded drugs are not FDA-approved: the agency does not review their safety, effectiveness or quality before they are sold, and a compounded drug is not the same as a generic ^[9][10]. It treats any claim that a compounded drug is the same as an approved one as a red flag ^[9].

The FDA says it has received adverse event reports linked to compounded tirzepatide prescribed at doses beyond the approved label, including faster dose increases. As of 31 May 2026 it had more than 730 reports associated with compounded tirzepatide, and it notes that such reports are likely underreported ^[9].

Much of the compounding of tirzepatide rested on its place on the FDA’s drug shortage list, where it had been since 2022. The agency issued its decision that the shortage is resolved on 19 December 2024, and its update page, current as of 1 April 2026, says tirzepatide is on neither the shortage list nor the 503B bulks list ^[11]. The article on compounded GLP-1 medicines goes through those rules step by step.

Fraudulent labels and "research" vials

The FDA reports fraudulent compounded tirzepatide in the US with false information on the label, sometimes naming pharmacies that do not exist or that did not make the product. In one reported case the person had a painful, swollen, reddened area with a lump where the injection went in ^[9].

It has also warned companies that sold tirzepatide and other unapproved substances, such as retatrutide, survodutide or mazdutide, straight to consumers with dosing instructions, under labels such as "for research purposes" or "not for human consumption". Some of these products are not tirzepatide at all: the FDA notes that retatrutide is not part of any approved drug and cannot be used in compounding ^[9].

Checking what you have

Both labels say tirzepatide should look clear and colorless to slightly yellow, and should not be used if you see particles or discoloration. With vials, they ask for a fresh syringe and needle each time, and a syringe able to measure the 0.5 mL or 0.6 mL dose. A KwikPen must never be shared, even with a new needle, because sharing can pass on blood-borne infections ^[1][2].

If your prescription moves from one presentation to another, say from single-dose pens to a KwikPen® or a vial, both labels ask that you and any carer are trained on the new device and read its own Instructions for Use ^[1][2].

If the name, strength or appearance does not match your prescription, ask your pharmacist or prescriber before using it. The FDA advises filling prescriptions at state-licensed pharmacies ^[9].

Record the product, not just the molecule

Writing only "tirzepatide" in a log hides useful details: the brand, the strength and whether it is a pen, a KwikPen or a vial. Those details matter when you or your clinician look back at a dose change, and they are what a pharmacist needs if a product ever has to be checked or reported.

Mounjaro® and Zepbound® are registered trademarks of Eli Lilly and Company. PepLabo is not affiliated with or endorsed by Eli Lilly and Company.

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