Prescription only
Tirzepatide
Sold as Mounjaro, Zepbound.
What the label states
Unusually for this page, the molecule does have one ladder. Both approved products start at 2.5 mg once weekly, escalate in 2.5 mg increments after at least 4 weeks on the current dose, and are supplied in the same six strengths (2.5, 5, 7.5, 10, 12.5, 15 mg). MOUNJARO states: “The recommended starting dosage of MOUNJARO is 2.5 mg injected subcutaneously once weekly… If additional glycemic control is needed, increase the dosage in 2.5 mg increments after at least 4 weeks on the current dose.” ZEPBOUND states: “The recommended starting dosage of ZEPBOUND for all indications is 2.5 mg injected subcutaneously once weekly for 4 weeks. The 2.5 mg dosage is for treatment initiation and is not approved as a maintenance dosage.” The adult maximum is 15 mg once weekly on both. Where they part company is the destination and the paediatric ceiling: ZEPBOUND names maintenance dosages (5, 10 or 15 mg for weight reduction; 10 or 15 mg for obstructive sleep apnoea) while MOUNJARO names none and leaves every step conditional on whether additional glycaemic control is needed — and MOUNJARO caps paediatric patients 10 years and older at 10 mg once weekly, a dosage ZEPBOUND does not have at all.
Quoted from the approved product label. Clinics commonly prescribe differently — more frequent, smaller injections of the same weekly total are routine — and where this site describes that, it is named as practice rather than as labelling.
- Route
- Subcutaneous once weekly, in the abdomen or thigh, or the back of the upper arm if someone else injects.
- Vehicle
- A clear, colourless to slightly yellow sterile aqueous solution at pH 6.5 to 7.5. Single-dose pens and vials contain sodium chloride, sodium phosphate dibasic heptahydrate and water for injection; multi-dose vials and KwikPens add benzyl alcohol, glycerin and phenol, because a container entered four times needs a preservative and a single-dose one does not.
- Usual barrel
- 100-unit insulin (1 mL)
- Strengths covered
- No strength page yet
Which syringe, and why
A 1 mL barrel, and for once the label says so rather than leaving it to inference: both labels instruct patients using vials to “use a syringe appropriate for dose administration (e.g., a 1 mL syringe capable of measuring a 0.5 mL or 0.6 mL dose)”. Tirzepatide is the only molecule on this page with an FDA-approved vial you actually draw from, which is why it gets a barrel at all. The trap is that the label prescribes in millilitres while the barrel is printed in units: a U-100 insulin syringe is graduated so 100 units make 1 mL, so the label’s 0.5 mL is 50 units and its 0.6 mL is 60 units, and “draw 0.6” read off an insulin barrel is a hundredth of the intended dose. The volume, not the milligrams, is what you measure here — a single-dose vial holds the whole prescribed dose in 0.5 mL whatever its strength, so every single-dose draw is the same 50 units regardless of whether it is 2.5 mg or 15 mg.
Administration
- 1
Know which presentation you were given
Tirzepatide ships four ways — a single-dose prefilled pen, a single-dose vial, a multi-dose vial and a single-patient-use KwikPen — and the labels require that patients be trained for their specific one and retrained if it changes. The vial presentations are drawn with a syringe; the pens are not.
- 2
Once weekly, any time of day, with or without meals
The day of the week can be changed if necessary, “as long as the time between the two doses is at least 3 days (72 hours).”
- 3
Inspect before drawing or injecting
“It should appear clear and colorless to slightly yellow. Do not use MOUNJARO if particulate matter or discoloration is seen.”
- 4
Draw the volume, not the milligrams
A single-dose vial is the whole dose in 0.5 mL — 50 units on a U-100 barrel. A multi-dose vial gives four injections of 0.6 mL — 60 units each. Always a new syringe and a new needle for every injection.
- 5
Rotate sites with each dose
Abdomen, thigh, or the back of the upper arm if someone else is injecting. When combined with insulin, give them as separate injections, never mixed, and not adjacent to one another even in the same region.
- 6
If you miss a dose, the window is 4 days
“If a dose is missed, instruct patients to administer MOUNJARO as soon as possible within 4 days (96 hours) after the missed dose. If more than 4 days have passed, skip the missed dose and administer the next dose on the regularly scheduled day.” Note this differs from semaglutide, where the window is 5 days.
- 7
Flag any planned surgery or procedure
Pulmonary aspiration during general anaesthesia or deep sedation has been reported in patients on GLP-1 receptor agonists, and the label directs telling providers about any procedure being planned.
Storage
- —Refrigerate at 2–8 °C. Do not freeze, do not use if frozen, protect from heat and light, and keep the product in its original carton.
- —Single-dose pen or single-dose vial: “If needed, each single-dose pen or single-dose vial can be stored unrefrigerated at temperatures not to exceed 30°C (86°F) for up to a total of 21 days.”
- —Unopened multi-dose vial or KwikPen: good to the expiry date if refrigerated; discard after 30 days if kept at room temperature.
- —Opened multi-dose vial or KwikPen: “Throw away opened multi-dose vial or single-patient-use KwikPen after a total of 30 days at room temperature, 30 days after first use, or after taking 4 weekly doses, even if there is medicine left in it.”
- —The 21-day and 30-day limits belong to different containers. Two tirzepatide presentations in the same fridge can have different discard dates.
Monitoring
| Marker | When | Why |
|---|---|---|
| Symptoms of thyroid C-cell tumour | Throughout, by symptom | The boxed warning directs counselling on a neck mass, dysphagia, dyspnoea or persistent hoarseness, and simultaneously states that routine calcitonin or thyroid ultrasound screening “is of uncertain value”. Tirzepatide is contraindicated outright with a personal or family history of medullary thyroid carcinoma or with MEN 2. |
| Signs of acute pancreatitis | After initiation and throughout | Acute pancreatitis, including fatal and non-fatal haemorrhagic or necrotising pancreatitis, has been observed with GLP-1 receptor agonists and with tirzepatide; the label directs discontinuing if it is suspected. |
| Renal function | When vomiting, diarrhoea or nausea are causing volume depletion | Same mechanism as the rest of the class — acute kidney injury follows dehydration rather than the drug acting on the kidney directly. Monitoring is event-driven, not scheduled. |
| Blood glucose, if also taking insulin or a sulfonylurea | Around initiation and each escalation | Concomitant use with an insulin secretagogue or insulin may increase the risk of hypoglycaemia, including severe hypoglycaemia; reducing the other agent may be necessary. |
| Weight or BMI response | Against the maintenance dosage chosen | ZEPBOUND directs considering treatment response and tolerability when selecting maintenance, and considering a lower maintenance dosage if one is not tolerated — the label treats maintenance as a choice among three, not as the top of a ladder you are obliged to climb. |
Frequently asked questions
- Is Mounjaro the same as Zepbound?
- Same molecule and the same ladder; different indications, different maintenance language and a different paediatric ceiling. Both start at 2.5 mg once weekly, both escalate in 2.5 mg steps after at least 4 weeks, both cap adults at 15 mg once weekly, and both ship in the same six strengths. MOUNJARO is for glycaemic control in type 2 diabetes and names no maintenance dose — every step is conditional on whether additional glycaemic control is needed, so any rung can be a destination. ZEPBOUND is for weight reduction and obstructive sleep apnoea and does name maintenance dosages, and it states that 2.5 mg “is for treatment initiation and is not approved as a maintenance dosage”. MOUNJARO also has a paediatric dosage capped at 10 mg weekly; ZEPBOUND has none.
- What is the concentration of tirzepatide in mg/mL?
- There is no single answer, and assuming there is one is how a dose comes out wrong. Single-dose pens and single-dose vials put the entire dose into 0.5 mL, so the concentration climbs with the strength — 5 to 30 mg/mL across the six strengths. Multi-dose vials and KwikPens deliver each dose in 0.6 mL from a 2.4 mL fill, which works out at 4.17 to 25 mg/mL. So 10 mg of tirzepatide is a 20 mg/mL solution in one container and a 16.7 mg/mL solution in another. Compounded tirzepatide has no concentration at all until bacteriostatic water is added, at which point the compounder’s vial strength divided by the water volume is the only figure that governs your draw.
- How many units is a tirzepatide dose on an insulin syringe?
- It depends on the presentation, and it is a volume question rather than a milligram one. A U-100 insulin syringe is graduated so 100 units equal 1 mL. Every FDA-approved single-dose vial holds the dose in 0.5 mL, which is 50 units, whatever the strength. Every injection from an approved multi-dose vial is 0.6 mL, which is 60 units. Neither figure transfers to compounded tirzepatide, where the concentration was set when the powder was reconstituted and the same 25-unit mark can be a very different dose. The units converter does that arithmetic against the numbers on your own vial.
- Why do tirzepatide multi-dose vials contain benzyl alcohol when single-dose ones do not?
- Because a container you enter four times has to stop bacteria growing between doses and a container you enter once does not. The single-dose presentations contain only sodium chloride, sodium phosphate dibasic heptahydrate and water for injection; the multi-dose vial and KwikPen add benzyl alcohol 5.4 mg, glycerin 4.8 mg and phenol 1.08 mg per dose. It is worth knowing if you have a benzyl alcohol sensitivity, and it is also the reason the opened multi-dose vial has a 30-day discard date rather than running to its printed expiry.
- How long can I be late with a weekly tirzepatide dose?
- Four days. “If a dose is missed, instruct patients to administer MOUNJARO as soon as possible within 4 days (96 hours) after the missed dose. If more than 4 days have passed, skip the missed dose and administer the next dose on the regularly scheduled day.” The dosing day can also be moved permanently so long as at least 3 days (72 hours) separate the two injections. Do not carry a semaglutide habit across: Ozempic’s window is 5 days, not 4.
Sources
- [1]FDA label — MOUNJARO (tirzepatide) injection, for subcutaneous use, Eli Lilly and Company. DailyMed SPL version 40, effective 2026-08-27, marketing category NDA (NDA215866)
- [2]FDA label — ZEPBOUND (tirzepatide) injection, for subcutaneous use, Eli Lilly and Company. DailyMed SPL version 40, effective 2026-08-28, marketing category NDA (NDA217806)
Related
Educational reference, not medical advice. Dose, route and whether this compound is appropriate at all are decisions for your clinician.