Mounjaro Dosage UK: Doses, When to Increase and Missed Doses

Mounjaro comes in six strengths, from 2.5 mg to 15 mg, and almost everyone starts on the lowest. This guide explains how the dose is increased, which doses are used long term, what the main trial found at each dose, what to do if you miss an injection and what each strength typically costs in the UK.

Mounjaro Doses at a Glance

Start at 2.5 mg for 4 weeks, then 5 mg; increase in 2.5 mg steps if needed; maintain on 5, 10 or 15 mg; 15 mg is the maximum.

Mounjaro (tirzepatide) is a once-weekly injection. The KwikPen comes in six strengths: 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg and 15 mg.

According to its Summary of Product Characteristics (SmPC):

• The starting dose is 2.5 mg once a week.

• After 4 weeks, the dose is increased to 5 mg once a week.

• If needed, it can then be increased in 2.5 mg steps, after at least 4 weeks on the current dose.

• The recommended maintenance doses are 5 mg, 10 mg and 15 mg.

• The maximum dose is 15 mg once a week.

No dose adjustment is needed based on age, sex, ethnicity or body weight, or for kidney or liver problems, although the SmPC advises caution where experience is limited, such as severe kidney or liver disease.

Why the Dose Starts Low and Goes Up Slowly

Stomach side effects are more common while the dose is increasing, so it goes up in small steps.

The most common side effects of Mounjaro affect the stomach and gut, such as feeling sick (nausea), diarrhoea, constipation and vomiting. In the weight management trials, these were mostly mild or moderate, and the SmPC notes that nausea, vomiting and diarrhoea were more common while the dose was being increased and became less common over time.

Starting at 2.5 mg and stepping up in 2.5 mg stages, at least 4 weeks apart, gives your body time to adjust before each increase.

Some symptoms need urgent attention at any dose. The SmPC says to seek immediate medical help for persistent, severe stomach pain, which can be a sign of acute pancreatitis. Report suspected side effects to the MHRA Yellow Card scheme.

When to Increase Your Mounjaro Dose

After 5 mg, only if needed and at least 4 weeks after the last increase, decided with your prescriber.

After the first 4 weeks on 2.5 mg, everyone moves up to 5 mg. Beyond 5 mg, an increase is not automatic: the SmPC says the dose can be increased if needed, after at least 4 weeks on the current dose. Some people stay on 5 mg; others go up to 10 mg or 15 mg.

Your prescriber decides with you whether to increase, based on how you are getting on, your weight loss and any side effects. If side effects are hard to manage, tell them before your next increase.

For weight management, the SmPC adds a review point: if someone has not lost at least 5% of their starting body weight 6 months after reaching their highest tolerated dose, a decision is needed on whether to continue treatment.

Which Mounjaro Dose Leads to the Most Weight Loss?

In SURMOUNT-1, all doses beat placebo, and 10 mg and 15 mg led to more weight loss on average than 5 mg.

SURMOUNT-1, published in the New England Journal of Medicine in 2022, randomly assigned 2,539 adults with obesity, or overweight with a weight-related condition, and without diabetes, to tirzepatide 5 mg, 10 mg or 15 mg or a placebo once a week for 72 weeks, alongside diet and activity advice. The dose was stepped up over the first 20 weeks.

All three doses led to more weight loss on average than placebo, and the 10 mg and 15 mg doses led to more than 5 mg. The difference between 10 mg and 15 mg was smaller than between 5 mg and 10 mg. These are averages across a trial funded by Eli Lilly, which makes Mounjaro, not a prediction for one person. A higher dose is not automatically better: the right dose for you balances how well it works for you against side effects, and your prescriber decides it with you.

Missed Doses and Changing Your Injection Day

Within 4 days, take it; after 4 days, skip it. Keep at least 3 days between doses.

The SmPC gives two rules:

• If you miss a dose, take it as soon as possible within 4 days. If more than 4 days have passed, skip the missed dose and take the next one on your usual day. Then carry on with your normal weekly schedule.

• To change your injection day, you can, as long as there are at least 3 days between two doses.

If you have missed more than one dose, speak to your prescriber before your next injection.

How Each Dose Is Injected

Under the skin of the stomach or thigh, or the back of the upper arm if someone else injects; new needle and priming each time; 4 doses per pen.

Mounjaro is injected under the skin of the stomach area (abdomen) or thigh. Another person can inject it into the back of your upper arm. You can inject at any time of day, with or without food, and the SmPC advises changing the injection site each time.

Each KwikPen holds 4 fixed doses of one strength, so one pen lasts 4 weeks, and when your dose changes you need a pen of the new strength. The KwikPen instructions for use set out the routine for every injection:

• Attach a new pen needle each time. Needles are not included with the pen.

• Prime the pen before injecting, by releasing a small amount of medicine into the air. This removes air and checks the pen is working.

• After 4 doses, throw the pen away. The instructions say not to try to inject any medicine left over, as there may not be enough for a full dose.

• Never share your pen with anyone, even with a new needle, because of the risk of infection.

Before first use, keep pens in the fridge. Once in use, the SmPC allows a pen to be kept out of the fridge for up to 30 days at no more than 30°C, after which it must be thrown away. Read the instructions for use in the pack before your first injection and with each new pen.

Other Medicines and Your Dose

Extra contraception for 4 weeks after starting and after each increase; stop 1 month before a planned pregnancy; insulin or sulphonylurea doses may be lowered.

Contraceptive pills. Mounjaro may make the contraceptive pill less effective. The SmPC advises women using oral contraceptives to switch to a non-oral method, or to add a barrier method such as condoms, for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase.

Pregnancy and breastfeeding. Mounjaro should not be used during pregnancy. If you want to become pregnant, the SmPC advises stopping it at least 1 month before, because it stays in the body for a long time. On breastfeeding, the SmPC says Mounjaro could be considered, as only very low amounts were found in breast milk; discuss it with your prescriber.

Diabetes medicines. If you take insulin or a sulphonylurea, your prescriber may lower that dose when you start Mounjaro, to reduce the risk of low blood sugar, and you will need to check your blood sugar.

Tell your prescriber about every medicine you take before you start and before each dose increase.

How Much Each Mounjaro Dose Costs

Typically £135.47 a pen at 2.5 mg, rising to £273.99 at 15 mg.

Privately, Mounjaro is priced by strength, and higher doses cost more. Across UK pharmacies, a 4-week pen typically costs £135.47 at 2.5 mg, £159.99 at 5 mg, £238.74 at 10 mg and £273.99 at 15 mg (collected on 7 November 2026).

These are medians across the UK pharmacies we track every day, so half charge less and half charge more. Because most people step up over the first months, the cost usually rises before it settles. For prices at every pharmacy and dose, see Mounjaro prices compared.

Scientific References

1. Mounjaro KwikPen solution for injection in pre-filled pen - Summary of Product Characteristics.
2. Jastreboff AM et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med 2022;387:205-216.
3. Mounjaro KwikPen - Instructions for Use.
4. MHRA Yellow Card scheme.

Frequently Asked Questions