Disadvantages of Mounjaro: An Honest UK Guide (October 2026)

01 · The honest list

The main disadvantages of Mounjaro

The biggest drawbacks are side effects, the injection routine, cost and the effort still required from you. Tirzepatide activates two gut-hormone receptors, GIP and GLP-1, and slows how quickly the stomach empties.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.¹³

Other disadvantages are practical: it is a once-weekly pen, it is prescription-only, and it is licensed for weight management and type 2 diabetes rather than for everyone.¹ For a wider view, see our guides to advantages and disadvantages of Mounjaro and GLP-1 disadvantages.

02 · Your decision

Is Mounjaro right for you?

It is right for you if a prescriber judges the benefits outweigh the downsides for your health. Mounjaro is used alongside a reduced-calorie diet and increased physical activity, and individual results vary.¹ If you are ready to explore it, the Mounjaro pen starts with a free consultation. A first 2.5mg pen costs £129.99 as a first-order price with code FIRST40 (standard price £169.99).

Related guides: Estradiol and mounjaro and Eds and mounjaro.

03 · Side effects and safety

Side effects and safety concerns

If you have a safety concern, speak to your prescriber or pharmacist. If you notice any new or lasting symptom, tell your prescriber, and you can report suspected side effects through the Yellow Card scheme.¹⁹ Our disadvantages of weight loss injections page covers the wider class.

04 · Results and effort

Results depend on your own effort

Mounjaro does not replace diet and activity, and trial averages do not predict your own result. In SURMOUNT-1, a trial of 2,539 adults, people taking tirzepatide alongside diet and exercise lost on average 15% of their body weight on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, compared with 3.1% with lifestyle changes alone.² Those are averages, and individual results vary.

Your prescriber reviews your progress and dose at your monthly check-ins.

05 · Stopping and clearance

Stopping Mounjaro

Tirzepatide has a half-life of about five days, so after a final dose it takes roughly four to five weeks to clear the system. There is no way to speed this up, and nothing needs doing while it clears.¹ If you stop, trial results show weight can come back: in SURMOUNT-4, people who stopped tirzepatide after 36 weeks regained on average 14% of body weight over the following year, while those who continued lost a further 5.5% on average. Plan any decision to stop with your prescriber rather than on your own.

06 · 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

07 · Cost and NHS access

Cost and NHS access

Cost is a genuine disadvantage of private treatment. A first year costs £2,711.88 at standard prices if you stay on 5mg after your 2.5mg starting pen, up to £3,599.88 if you step up through every dose to 15mg. A new customer's first order is £40 less and every later order £25 less.

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.⁴⁶ Many people who meet the licensed criteria choose regulated private treatment rather than wait. See our weight loss clinic for options.