Mounjaro's active substance, tirzepatide, is a dual GIP and GLP-1 receptor agonist — the first medicine of its kind at approval.[4] The dosing schedule below is the one set out in the MHRA authorisation and the UK Summary of Product Characteristics (SmPC).[2][1]
Six once-weekly strengths — 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg. Everyone starts at 2.5mg for four weeks, moves to 5mg, and any further increases come in 2.5mg steps no more often than every four weeks, up to 15mg. The maintenance doses are 5mg, 10mg and 15mg, and the pace is set by the prescriber, not the patient.[2][1]
The six Mounjaro pen strengths
Mounjaro is supplied in six fixed strengths, each delivered as the same small 0.6mL injection.[1] Higher pens hold more medicine in the same volume — a bigger dose is not a bigger injection.
| Strength (once weekly) | Role in treatment |
|---|---|
| 2.5mg | Starting dose — the first four weeks only, to help the body adjust |
| 5mg | First therapeutic dose; the lowest maintenance dose |
| 7.5mg | Titration step between 5mg and 10mg |
| 10mg | Middle maintenance dose |
| 12.5mg | Titration step between 10mg and 15mg |
| 15mg | Maximum dose and highest maintenance dose |
One pen, four doses: the KwikPen
In the UK, Mounjaro comes as the KwikPen — a disposable, single-patient pre-filled pen holding four fixed weekly doses of 0.6mL, one pen per strength — so a pen covers roughly a month, matching the four-week rhythm of titration.[1] Unopened pens are kept in the fridge at 2°C to 8°C and never frozen; a pen in use may be kept out of the fridge at up to 30°C for up to 30 days, after which it must be discarded even if medicine remains.[1] The patient information leaflet in your pack carries the full storage and handling instructions — follow the copy in your box.
Once a week, any day: how Mounjaro is taken
One injection, once a week, under the skin of the abdomen, thigh or upper arm, rotating the site each time. It can be given on any day of the week, with or without food, so there is room to pick a day that suits your routine.[1] We cover technique, site rotation and pen handling step by step on our how to inject Mounjaro page.
The 4-week step-up ladder
Nobody starts on a high dose. Tirzepatide is titrated — started low, increased in stages:[2][1]
| Step | Once-weekly dose | Minimum time at this step |
|---|---|---|
| Start | 2.5mg | 4 weeks |
| Then | 5mg | At least 4 weeks before any further increase |
| If increased | 7.5mg → 10mg → 12.5mg | No more often than every 4 weeks per 2.5mg step |
| Maximum | 15mg | — |
The 2.5mg start is described as a non-therapeutic initiation dose: its whole job is to improve gastrointestinal tolerability before you reach a dose that does the therapeutic work.[2] Beyond 5mg, increases come in 2.5mg steps, no more often than every four weeks, up to 15mg — as tolerated, and as directed by the prescriber.[2]
What the ladder is not
- "Every four weeks" is a minimum, not a target. A prescriber can hold a dose for longer, or step back down, if side effects are troublesome.
- You do not have to reach 15mg. The maintenance doses are 5mg, 10mg and 15mg,[1] and someone doing well on a lower one may simply stay there.
- The pace is prescriber-led. Patients do not adjust the dose themselves, skip rungs, or "borrow" a stronger pen.
Maintenance dosing: 5mg, 10mg or 15mg
Once titration is finished, treatment settles onto a maintenance dose. The UK label names three — 5mg, 10mg and 15mg once weekly.[1] The 7.5mg and 12.5mg pens are stepping stones between those levels, not long-term destinations.
These are also the doses the obesity evidence was built on. SURMOUNT-1, a 72-week trial in 2,539 adults with obesity or overweight and without type 2 diabetes, tested tirzepatide at 5mg, 10mg and 15mg against placebo.[3] At the top dose, 96% of participants lost at least 5% of their body weight, and 39.7% lost 25% or more, against 0.3% on placebo.[5] The composition of the loss mattered too: fat mass fell roughly three times more than lean mass — about 33.9% against 10.9%.[5] In people who also have type 2 diabetes the numbers run lower — 13.4% average loss on 10mg and 15.7% on 15mg in SURMOUNT-2, versus 3.3% on placebo[2] — a consistent class pattern, not a quirk.[3] Which maintenance dose someone settles on is the prescriber's judgement, weighing response against tolerability; higher is not automatically better.
Why the dose goes up so slowly
The slow climb is not caution for its own sake. Stepwise escalation is used specifically to reduce tirzepatide's dose-related gastrointestinal side effects.[3] In SURMOUNT-1 the most common side effects were gastrointestinal, mostly mild to moderate, and several clearly tracked the dose: nausea affected 24.6% of people on 5mg, 33.3% on 10mg and 31.0% on 15mg, against 9.5% on placebo; diarrhoea rose from 18.7% on 5mg to 23.0% on 15mg; vomiting from 8.3% to 12.2% across the same range.[3] Constipation was common too, though it did not follow the dose the same way — 16.8% on 5mg, 17.1% on 10mg, 11.7% on 15mg.[3]
At least four weeks at each rung is how the schedule tries to keep those effects manageable. Even so, some people stop: discontinuation because of adverse events in SURMOUNT-1 was 4.3% on 5mg, 7.1% on 10mg and 6.2% on 15mg, against 2.6% on placebo.[3] Our Mounjaro side effects page covers the full picture, including rarer serious risks and who should not take it.
If a step up brings side effects you are struggling with, that is exactly what the four-week minimum — and the option to pause or step back down — is for. Do not push through severe or persistent symptoms, and do not adjust the dose yourself: speak to your prescriber or pharmacist.
What if you miss a dose?
The exact missed-dose rule for Mounjaro is set out in the SmPC and the patient information leaflet inside your pack — and the leaflet is where to check it, because label instructions are updated from time to time and the copy in your box is the one that applies to your pen. If you are unsure, ask your prescriber or pharmacist.
Two principles hold regardless: never inject extra to "make up" a missed dose unless a healthcare professional tells you to; and if you want to change your usual injection day — possible, since any day works[1] — ask how to move it safely rather than improvising.
Who can take Mounjaro — and how it is accessed in the UK
Mounjaro is licensed in the UK, but access runs entirely through a prescriber: there is no legitimate way to choose a dose and buy the pens yourself. The MHRA authorised it for weight management in adults aged 18 and over on 8 November 2023 — for a BMI of 30kg/m² or more, or 27 to 30kg/m² with at least one weight-related health problem such as prediabetes, high blood pressure, abnormal blood fats or cardiovascular disease — always alongside a reduced-calorie diet and more physical activity.[2] Meeting those criteria does not make the medicine right for any individual; that is what the consultation is for.
On the NHS, access is deliberately narrow and phased. NICE recommended tirzepatide in appraisal TA1026, published 23 December 2024,[6] and NHS England began a phased primary-care rollout on 23 June 2025 for those with the highest clinical need first — around 220,000 people over the first three years, with diet and activity support alongside.[7] Broad, open NHS access is not available now. Outside the NHS, a prescription can be issued privately by a qualified prescriber after a proper consultation. We do not recommend, rank or link to any provider.
In the UK, Mounjaro is available for weight loss on prescription only, after a consultation with a qualified prescriber.[2] Treat any site offering it with no prescription or no consultation with real caution. The MHRA's FakeMeds campaign has advice on buying medicines safely online and on checking a seller before you buy.
Frequently asked questions
What strengths does Mounjaro come in?
How often do you inject Mounjaro?
Once a week — any day, with or without food — under the skin of the abdomen, thigh or upper arm, rotating the site each time.[1]
How quickly can the Mounjaro dose be increased?
What is the maximum dose of Mounjaro?
15mg once weekly. Not everyone needs it: 5mg, 10mg and 15mg are all maintenance doses, chosen by the prescriber on response and tolerability.[1]
What should I do if I miss a dose of Mounjaro?
Check the patient information leaflet in your pack — it sets out the exact rule — or ask your prescriber or pharmacist. Never inject extra to make up a missed dose unless a healthcare professional tells you to.
Is Mounjaro safe?
It is licensed by the MHRA,[2] meaning its benefits and risks have been formally assessed — but no medicine is risk-free. The most common side effects are gastrointestinal, mostly mild to moderate and dose-related,[3] and some people should not take it at all — which is what the prescriber screens for. See our side effects page for the full picture.
Can you buy Mounjaro online without a prescription?
No. In the UK, Mounjaro is available on prescription only — whether through the phased NHS rollout or a private prescriber after a consultation.[2] The MHRA's FakeMeds campaign has advice on buying medicines safely online.
If you experience side effects from any medicine, you can report them through the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk,[8] and speak to your GP or pharmacist.
References
- electronic medicines compendium (emc). Mounjaro KwikPen — Summary of Product Characteristics. medicines.org.uk
- MHRA / GOV.UK. MHRA authorises diabetes drug Mounjaro (tirzepatide) for weight management and weight loss. 8 November 2023. gov.uk
- Jastreboff AM et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). New England Journal of Medicine, 2022. nejm.org
- Eli Lilly and Company. FDA approves Lilly's Mounjaro (tirzepatide) injection, the first and only GIP and GLP-1 receptor agonist. Investor news release, 2022. investor.lilly.com
- Eli Lilly and Company. Lilly's SURMOUNT-1 results published in the New England Journal of Medicine. Investor news release, 2022. investor.lilly.com
- National Institute for Health and Care Excellence. Tirzepatide for managing overweight and obesity (TA1026). 23 December 2024. nice.org.uk
- NHS England. Interim commissioning guidance: NICE TA1026 tirzepatide. england.nhs.uk
- MHRA. Yellow Card scheme — report a side effect. yellowcard.mhra.gov.uk