I'm On Mounjaro and Not Losing Weight: Why It Happens and What to Do (October 2026)

01 · The core answer

Is it normal to not lose weight on Mounjaro?

Yes, a slow or stalled start is common enough that it should not alarm you, but it is worth investigating rather than waiting indefinitely. Mounjaro is a tool that changes appetite. The scale only moves when that change in appetite turns into a sustained gap between what you eat and what you use.

Tirzepatide activates two natural gut-hormone receptors, and in practice most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet.¹ Notice the wording: it supports a reduced-calorie diet. It does not replace one.

The pivotal trial results show the same thing. In the SURMOUNT-1 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 across a large group. Some people lost far more and some lost far less, which is why individual results vary.

02 · Your next step

What should I check first if the scale isn't moving?

Start with the cause you can verify yourself today, then move to the ones that need your prescriber.

If you are supplied by us, your monthly clinical review is the natural place to raise a stall. It is included, and the prescribing team can look at your dose and progress together. If you are still deciding on treatment, our weight loss clinic explains how the service works.

Prefer to compare notes by dose? Our guides cover not losing weight on 5mg, on 10mg and on 15mg, and there is a longer general explainer in why you may not be losing weight on Mounjaro in the UK.

03 · Calories still count

Calories still count on Mounjaro

The most common reason for a stall is that appetite has dropped but energy intake is still level with energy use. The medicine helps you feel fuller sooner. It does not stop you eating, and it does not burn fat on its own.

The trial wording is clear on this point: these are trial averages — individual results vary, and treatment works alongside a reduced-calorie diet and increased physical activity, not instead of them.² The people in the trial who lost the most were also following a lifestyle programme.

Smaller appetite can hide a quieter problem. When meals shrink, many people drift towards soft, calorie-dense foods because they are easy to eat while feeling full. Think crisps, biscuits, ice cream, pastries, cheese and nut butters. Small amounts add up quickly, and you may not notice them in your head even though they show up on a diary.

Liquid calories are the other classic blind spot. Sweetened coffees, juices, smoothies, milky drinks, fizzy drinks and alcohol do not fill you up the way solid food does, so the medicine's fullness effect does little to cap them. If you have a few of these a day, swapping them can change the picture without feeling like a big sacrifice.

A practical way to test this is to keep an honest food diary for a couple of typical weeks, including drinks and tastes while cooking. You do not need to do it forever. The aim is to see what the diary says compared with what it feels like you are eating. The GLPTrackr companion app is free on iOS and Android if you want somewhere to log it alongside your injection dates.

04 · Dose and time

Does my dose or time on treatment matter?

Yes, both matter, and they are the reasons to raise with your prescriber rather than fix alone. Mounjaro comes as a pre-filled multi-dose pen in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹ Which strength suits you is a prescribing decision, made during your reviews.

The trial data shows why dose comes into the conversation. Average loss in the pivotal trial rose with strength: 15% on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks.² That is an average across many people, not a promise that a higher dose will work faster for you, and a higher strength is not automatically better for every person or every side-effect profile.

Time matters too. Treatment is built as a stepped process, and the early weeks are not the whole story. Judging the medicine after only a few injections, particularly at a starting strength, can be misleading. The trial itself ran for 72 weeks, which tells you this is designed as a long course, not a quick fix.

If you want dose-specific detail, these guides cover what people commonly check at each stage: not losing weight on 7.5mg and on 12.5mg. Dose changes should come from your prescriber.

New customers get £40 off a first order with code FIRST40, and an automatic £25 reorder discount applies to every future order (code DOSE25).

05 · Weight that was lost then stalled

What if I lost weight at first and then stalled?

A plateau after an early drop is common and does not mean the medicine has stopped working. Weight does not fall in a straight line. Water, digestion, hormones, salt intake, bowel habits and training can all move the scale up or down from one week to the next without any change in fat.

Look at trends rather than single weigh-ins. Weigh yourself at the same time of day, under the same conditions, and compare averages over a few weeks. Waist, how clothes fit and photos can show progress that the scale hides.

It also helps to remember that as you lose weight your body needs less energy. The portions that produced loss at your starting weight may simply hold you steady at a lower one. That is usually a cue to look again at diet and activity, and to raise it at your review, rather than a sign of failure.

We cover this situation in more depth in Mounjaro not losing weight anymore. If your weight has been flat for a long stretch, or has started to climb, ask your prescriber for a proper review rather than waiting. 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.

06 · Pen and injection checks

Could my pen or injection routine be the problem?

It is worth ruling out, because the fix is simple. Mounjaro is a once-weekly injection, so a routine matters. Pick a day, set a reminder and use the pen exactly as the patient information leaflet describes. Follow the pen's instructions for each step of the injection.¹³

Storage matters too. Store unopened pens in the fridge at 2–8°C until first use, and they keep until the printed expiry date. Once in use, a KwikPen 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.¹ Do not use a pen that has been above 30°C or has been frozen. Check the leaflet and contact the pharmacy that supplied it.

If you have missed injections, or you are unsure whether a dose went in properly, tell your prescriber rather than guessing at a make-up dose. They will tell you what to do.

Finally, make sure your pen is genuine. Counterfeit and unlicensed weight-loss injections circulate online, and the MHRA warns about them.⁷ Our Mounjaro comes from official LillyDirect supply, direct from Eli Lilly's UK distribution, and is supplied only after a free online consultation reviewed by a GPhC-registered prescriber. Anyone offering to supply without a consultation or prescription should be avoided.

07 · Other factors to raise

Could something else be affecting my weight?

Sometimes, yes, and that is a conversation for your prescriber or GP rather than something to self-diagnose. Other medicines, changes in health, poor sleep, high stress and big changes in activity can all influence weight and appetite.

Tell your prescriber about any new medicine, including over-the-counter products and supplements, and about any change in your health since you started.

Also let your prescriber know if you take oral contraceptives. The SmPC advises switching to a non-oral method, or adding a barrier method (such as condoms), for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase.¹ The medicine can reduce absorption of oral contraceptives because stomach emptying slows, so your prescriber can advise on what suits you.⁷ If you take insulin or sulfonylureas, doses may need adjusting because of the risk of low blood sugar, so this should always be discussed with your prescriber.

If you notice any new or worrying symptom, speak to your prescriber and report it through the MHRA Yellow Card scheme.¹⁹ 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 the skin or eyes (possible gallbladder problems), or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing need immediate attention: seek immediate medical help.

08 · When to ask for a change

When should I ask my prescriber to change something?

Ask for a review when you have checked the basics and progress is still absent over a sustained period, rather than after a single quiet week. Bring evidence: your injection dates, weekly average weights, a few weeks of food diary and a note of your appetite and side effects.

A review can lead to several outcomes. Your prescriber may suggest staying at your current strength for longer, discuss whether a different strength suits you, review other medicines, or suggest more support with diet and activity. They may also say that treatment is working better than the scale suggests.

If Mounjaro does not suit you, other licensed options exist. Some people consider a Wegovy pen, which is semaglutide, a single-action medicine; the prescriber decides when to switch and which dose to start on, and Wegovy's licensed dose ladder starts at 0.25mg. If you are coming from the other direction, see not losing weight on semaglutide: should I switch to tirzepatide?. Either way, switching is a prescriber decision, not a quick fix.

NHS access to Mounjaro 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, and the primary-care rollout began in June 2025 with the highest-need groups first.⁴ If you are on the NHS pathway, your NHS team will review you through that service.

If you want to see how our service handles reviews, our page on a UK registered pharmacy for weight-loss medicines explains who we are and how we are regulated (GPhC 9012878).

09 · Realistic expectations

What are realistic expectations on Mounjaro?

Realistic means expecting a gradual change, not a steady weekly drop. The trial figures are averages from people who followed a lifestyle programme, and no average predicts your own result.

It helps to define success beyond the scale. Smaller portions, fewer cravings, easier choices around food, better fit of clothes and steadier energy are all signs the treatment is doing something, even in weeks when the number does not change.

It also helps to understand what comes after. Mounjaro is a long-term treatment decision. If you stop, tirzepatide has a half-life of about five days, so it takes four to five weeks to clear the system, and nothing needs doing while it clears.¹ Talk to your prescriber before stopping, so that you have a plan for diet and activity afterwards.

Mounjaro is a prescription-only medicine, supplied only after an online consultation reviewed by a GPhC-registered prescriber. It is used alongside a reduced-calorie diet and increased physical activity. Individual results vary. This page is information, not a substitute for medical advice.¹