Tirzepatide 2.5 mg Subcutaneous Pen Injector (October 2026)

01 · Price and ordering

What the 2.5mg pen costs and how to get it

The standard price of one 2.5mg pen (four weeks) is £169.99. Your first 2.5mg pen costs £129.99 with code FIRST40. Every later order is £25 off the standard price (code DOSE25). All six doses are in stock, and you can see the full range on the Mounjaro pen page.

Across the UK pharmacies we track, the cheapest 2.5mg starting pen is £143.96 and the dearest is £179.99 (checked 10 October 2026).

Our Mounjaro comes through official LillyDirect supply, so these are genuine KwikPens. Needles, a sharps bin and injection guidance come with every order. Ongoing monthly reviews are included, and you can pay by card, Klarna or pay-monthly with no subscription.

02 · NHS or private

NHS or private supply

Mounjaro is available on the NHS, but access is being phased in over several years. NICE recommends it for adults with a BMI of at least 35 plus at least one weight-related condition. The primary-care rollout began in June 2025 with the highest-need groups first, initially BMI 40+ with four or more qualifying conditions.⁴ Because full rollout will take years, many people who meet the licensed criteria choose regulated private treatment. For wider options see all weight loss treatments.

Related guides: Tirzepatide 2.5 mg 0.5 ml solution pen injector and Tirzepatide soln pen injector 2.5 mg 0.5 ml.

03 · What it is and how it works

What the tirzepatide 2.5mg pen is

Mounjaro is the brand name for tirzepatide, a once-weekly injectable prescription medicine made by Eli Lilly. In the UK it is licensed for weight management in adults and for type 2 diabetes. It comes as a pre-filled multi-dose pen (KwikPen) in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹ The brand name for tirzepatide in the UK is therefore Mounjaro. Our pages on the Mounjaro injector pen and the Mounjaro 2.5 mg/0.5 ml pen cover the same product.

Tirzepatide activates two natural gut-hormone receptors at once: GIP and GLP-1. Together these help regulate appetite, slow how quickly the stomach empties and improve the way the body responds to insulin. Most people feel fuller sooner and less hungry between meals. This dual action distinguishes it from single-action medicines such as semaglutide (Wegovy/Ozempic).¹

04 · Is 2.5mg enough?

Is 2.5mg enough to lose weight?

The 2.5mg dose is a starting dose, about letting your body adjust rather than weight loss itself. After at least 4 weeks the dose increases to 5mg, then can step up by 2.5mg at minimum 4-week intervals (7.5mg, 10mg, 12.5mg) to a maximum of 15mg weekly. Many people settle at 5mg, 10mg or 15mg. Higher is not automatically better.¹¹

Some people notice appetite change and early loss in week one; others feel little until a higher dose. Both are normal. Early loss includes water weight, so the trend matters more than any single weigh-in.¹

In SURMOUNT-1 (2,539 adults), people on tirzepatide alongside diet and exercise lost on average 15% of body weight on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, versus 3.1% with lifestyle changes alone. For someone starting at 100 kg, 20.9% is about 21 kg. These are trial averages and individual results vary.² If you have lost less than 5% of your starting weight after 6 months on the highest dose you can tolerate, your prescriber will discuss whether continuing or stopping is right for you.⁴

05 · How to inject

How to use the pen

Inject under the skin once a week, on the same day each week, at any time of day, with or without food. Licensed sites are the stomach area (at least 5cm from the belly button), the front of the thigh, or the back of the upper arm if someone else gives the injection. Rotate the site each dose.¹

Turn the dose knob until the correct dose shows in the window. Follow the pen's instructions for the rest.

If you miss a dose, take it within 4 days (96 hours) of the scheduled time. After more than 4 days, skip it and take the next on your usual day. Never take two doses within 3 days of each other. You can change your injection day if at least 3 days (72 hours) have passed since your last dose.¹

06 · Storage and travel

Storing and travelling with the pen

Keep pens in a fridge at 2–8°C and never freeze them. Once in use, a pen can be kept out of the fridge at a temperature not above 30°C for up to 30 days after first use, and must then be thrown away. Do not use a pen that has been above 30°C or has been frozen. Keep the cap on to protect it from light.¹ Unopened pens stay in the fridge until the printed expiry date. If one has been out of the fridge, check the leaflet and the pharmacy before using it.¹³

You can fly with Mounjaro. Carry pens in hand luggage, as hold luggage can fall below freezing, ideally in a cool bag with your prescription label.¹

07 · Safety and eligibility

Who can use it

Mounjaro is licensed for weight management in adults with a BMI of 30 or above, or between 27 and 30 with at least one weight-related condition such as high blood pressure, high cholesterol, obstructive sleep apnoea, cardiovascular disease, prediabetes or type 2 diabetes. It must be used alongside a reduced-calorie diet and increased physical activity.¹

The most common side effects, affecting more than 1 in 10 people, are nausea, diarrhoea, vomiting, constipation and abdominal discomfort. They are most likely when starting treatment or moving up a dose, and for most people they ease within days to a few weeks.¹ Report any side effect via the Yellow Card scheme.¹⁹ Mounjaro is prescription-only, supplied after an online consultation reviewed by a GPhC-registered prescriber. See also the Mounjaro injection 2.5 mg price guide.

08 · Serious side effects

Serious side effects: when to get help straight away

Serious side effects are uncommon but need urgent attention. Seek immediate medical help for: severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion) — your prescriber may need to adjust those medicines.¹