Mounjaro vs Zepbound Dosing: Same Drug

Last updated: June 2026

Mounjaro and Zepbound are the same active drug — tirzepatide — sold under two brand names by the same manufacturer: Mounjaro is approved for type-2 diabetes, and Zepbound is approved for chronic weight management and obstructive sleep apnoea. Their pens use an identical dose ladder (2.5, 5, 7.5, 10, 12.5, 15 mg once weekly), so the milligram dose carries across, and the number of syringe units you draw from a compounded vial depends only on the vial's concentration — not on which brand name is on the box.

Have a vial strength and a target dose? Convert any tirzepatide dose to exact mL and U-100 syringe units in seconds.

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TL;DR — key takeaways

One molecule, two labels. Mounjaro and Zepbound are both tirzepatide, a dual GIP/GLP-1 receptor agonist made by Eli Lilly. The difference is the approved indication, not the chemistry.
Identical dose ladder. Both pens titrate 2.5 → 5 → 7.5 → 10 → 12.5 → 15 mg once weekly, with a minimum of 4 weeks at the 2.5 mg starting dose.
5 mg of Mounjaro = 5 mg of Zepbound. A milligram of tirzepatide is a milligram regardless of brand; there is no conversion factor between the two.
Units follow the vial, not the brand. How many units you draw is set by the concentration (mg/mL) of your specific vial, which is what a units calculator works out.
This is an education and maths tool, not medical advice — follow your prescriber's titration plan.

Why one drug has two names

Tirzepatide first reached the US market in 2022 as Mounjaro, approved to improve blood-sugar control in adults with type-2 diabetes. In late 2023 the same molecule was approved a second time, under the brand name Zepbound, for chronic weight management in adults with obesity or overweight plus a weight-related condition; Zepbound later added an indication for moderate-to-severe obstructive sleep apnoea in adults with obesity. Two brand names let the manufacturer market, price, and label the drug separately for diabetes versus weight management, but the prescribing information for each lists the same active ingredient and the same single-dose pen strengths.

Tirzepatide is a dual agonist: it activates both the glucose-dependent insulinotropic polypeptide (GIP) receptor and the glucagon-like peptide-1 (GLP-1) receptor. That dual action promotes glucose-dependent insulin secretion, slows gastric emptying, and reduces appetite — the same pharmacology whether the box says Mounjaro or Zepbound. Its elimination half-life is roughly five days, which is why both are dosed once weekly and reach steady state after about four to five weeks of a given dose.

Side-by-side: Mounjaro vs Zepbound

Property	Mounjaro	Zepbound
Active ingredient	Tirzepatide	Tirzepatide
Drug class	GIP + GLP-1 dual agonist	GIP + GLP-1 dual agonist
Approved use	Type-2 diabetes	Weight management; obstructive sleep apnoea
Starting dose	2.5 mg / week	2.5 mg / week
Dose ladder	2.5, 5, 7.5, 10, 12.5, 15	2.5, 5, 7.5, 10, 12.5, 15
Min step interval	4 weeks	4 weeks
Maximum dose	15 mg / week	15 mg / week
Route	Subcutaneous, once weekly	Subcutaneous, once weekly
Approx. half-life	~5 days	~5 days

Figures reflect the FDA-approved Mounjaro and Zepbound prescribing information. The columns are deliberately near-identical — that is the whole point. Compounded vials are drawn manually and require you to calculate the volume yourself, and any prescribed protocol may differ, so follow your prescriber's instructions.

The shared titration ladder, visualised

Both brands climb the same staircase: start at 2.5 mg, hold each rung for at least four weeks, and step up only as tolerated toward a 15 mg ceiling.

The ladder above is identical for Mounjaro and Zepbound because it is the tirzepatide ladder — the brand on the box does not change it.

Turning a tirzepatide dose into syringe units

If you are using a compounded vial rather than a pre-filled pen, the milligram dose is not what you read on the syringe — you read units. A U-100 insulin syringe holds 100 units per 1 mL. The conversion is always the same: find the concentration (mg/mL), divide your dose by it to get mL, then multiply by 100 to get units. Nothing in this maths depends on whether the prescription says Mounjaro or Zepbound.

Worked example 1 — starting dose

Vial reconstituted to 10 mg/mL, starting dose 2.5 mg/week.

2.5 mg ÷ 10 mg/mL = 0.25 mL. 0.25 mL × 100 units/mL = 25 units.

Draw 25 units on a U-100 syringe.

Worked example 2 — second rung

Same 10 mg/mL vial, stepped up to 5 mg/week.

5 mg ÷ 10 mg/mL = 0.5 mL. 0.5 mL × 100 units/mL = 50 units.

Draw 50 units — half of a 1 mL syringe.

Worked example 3 — same dose, stronger vial

The same 5 mg dose from a 20 mg/mL vial: 5 ÷ 20 = 0.25 mL × 100 = 25 units.

Double the concentration, half the units — for the identical milligram dose. "Mounjaro vs Zepbound" never changes this; only the vial strength does.

Worked example 4 — top of the ladder

Maintenance dose 15 mg/week from a 20 mg/mL vial.

15 mg ÷ 20 mg/mL = 0.75 mL. 0.75 mL × 100 units/mL = 75 units.

Draw 75 units. The same 15 mg from a 10 mg/mL vial would be 1.5 mL — more than a 1 mL syringe holds.

Dose-to-units reference chart

Every rung of the shared tirzepatide ladder, shown as units on a U-100 syringe at two common compounded concentrations. Always confirm against your own vial label.

Weekly dose	At 10 mg/mL	At 20 mg/mL
2.5 mg (start)	25 units	12.5 units
5 mg	50 units	25 units
7.5 mg	75 units	37.5 units
10 mg	100 units	50 units
12.5 mg	— (over 1 mL)	62.5 units
15 mg (max)	— (over 1 mL)	75 units

Notice the gap at 12.5 and 15 mg from a 10 mg/mL vial: those doses need more than 1 mL, so a higher-concentration vial is used for the larger rungs. If your draw exceeds 1 mL, ask your pharmacy about a stronger vial.

How this is calculated

Every figure on this page uses two facts only: a U-100 syringe holds 100 units per mL, and concentration is dose-per-volume. There is no brand-specific or drug-specific constant — the arithmetic is identical for Mounjaro, Zepbound, or any vialled tirzepatide. The tirzepatide calculator automates exactly this and lets you sanity-check the result against the chart above. None of this is medical advice; it is the maths behind a dose your prescriber has set. Brand name affects packaging, indication, and price — never the units you draw for a given milligram dose at a given concentration.

Frequently asked questions

Are Mounjaro and Zepbound the same drug?

Yes. Both are tirzepatide, a dual GIP/GLP-1 receptor agonist made by Eli Lilly. Mounjaro is the brand approved for type-2 diabetes; Zepbound is the brand approved for chronic weight management and obstructive sleep apnoea. The active ingredient and the pen dose strengths are the same.

Does 5 mg of Mounjaro equal 5 mg of Zepbound?

Yes. A milligram of tirzepatide is a milligram regardless of which brand name is on the box. There is no conversion factor between Mounjaro and Zepbound — the dose ladders are identical.

Will I draw a different number of units for Zepbound than for Mounjaro?

No. Units depend on the concentration of your vial, not the brand. A 5 mg dose from a 10 mg/mL vial is 50 units whether the prescription says Mounjaro or Zepbound. Only the vial strength changes the units.

Why are there two names if it is one drug?

Two brand names let the manufacturer market, label, and price the drug separately for diabetes versus weight management. Each brand has its own FDA approval and prescribing information, but both list tirzepatide as the active ingredient.

Can I switch between Mounjaro and Zepbound at the same dose?

Because they are the same molecule at the same strengths, the milligram dose carries across, but switching is still a clinical decision for your prescriber, who manages the indication, supply, and titration. Do not change brands or doses on your own.

Sources

This guide is for general educational purposes only and does not constitute medical advice. Always follow your prescriber’s specific instructions and consult a qualified clinician before changing any protocol.