How Much Weight Can You Lose on Weight Loss Injections? (October 2026)

01 · The core answer

How much weight can you lose with weight loss injections?

Most people lose a meaningful share of their starting body weight over many months, and the amount depends heavily on the medicine, the dose you reach and how long you stay on it. Mounjaro (tirzepatide) is a weekly injection licensed for weight management in adults.¹

The 20.9% figure is a trial average, measured at the end of a long course on the highest dose. It is not what most people see in the first weeks, and it is not a promise.

For a detailed breakdown on the main product, see our guide on how much weight you can lose taking Mounjaro.

02 · Your next decision

Is this realistic for you, and what next?

The honest answer is that it depends on your starting point, your dose, your eating and activity, and how your body responds. Only a prescriber who has reviewed your health can judge whether treatment suits you. Our consultation is free, and every request is reviewed by a GPhC-registered prescriber.

If you are ready to look at treatment, you can see current options on the Mounjaro pen page. Your first 2.5mg pen costs £129.99 with code FIRST40 (standard price £169.99). For a wider view of support, visit our weight loss clinic, or read our breakdown of what weight loss injections cost before you decide.

03 · Trial results by dose

What the SURMOUNT-1 trial found

Tirzepatide's weight-management evidence is summarised by the SURMOUNT-1 trial. 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

These are trial averages — individual results vary, and treatment works alongside a reduced-calorie diet and increased physical activity, not instead of them.²

Averages hide the spread. At 72 weeks, 85% of participants on 5mg, 89% on 10mg and 91% on 15mg had lost at least 5% of their body weight. Half of participants on 10mg and 57% on 15mg lost at least 20% of their body weight.²

Read that spread as a reminder that some people lose far more than the average and some far less. The dose matters too: the trial figures rise with each higher dose, but your prescriber decides your pace based on how you tolerate treatment. Many people settle at a maintenance dose of 5mg, 10mg or 15mg, and higher is not automatically better.¹

If you are already on a particular strength, our guides on results on Mounjaro 5mg and results on 12.5mg Mounjaro go dose by dose.

04 · Month by month pace

How quickly do you lose weight with weight loss injections?

Weight loss on Mounjaro is gradual by design. The first weeks on 2.5mg are an adjustment phase and losses are usually modest; most measurable progress builds from 5mg onward, month by month.² Trials measured results at 72 weeks — think in months, not days, and judge progress by trend, not individual weigh-ins.

The 2.5mg starting weeks are about adjustment, and experiences differ widely: 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 over weeks matters more than any single weigh-in.¹

That is why a question like "can I lose a large amount very fast?" has a cautious answer. Rapid early drops are possible for some people, but they are not the design of the treatment and not a target. After at least 4 weeks the dose increases to 5mg, and it can then step up by 2.5mg at a minimum of 4-week intervals up to a maximum of 15mg weekly, depending on how you respond and tolerate it.¹

What to expect after a few months

Three months in, most people are still on the lower rungs of the dose ladder, so trial-average losses at this stage are modest compared with the headline figures: in SURMOUNT-1, average weight loss built month by month, with the full 15–21% averages measured at 72 weeks, not 12. A sensible 3-month expectation on a standard titration is mid single digits as a percentage of body weight, with wide individual variation. Slower early progress does not predict failure — the dose you respond to may still be ahead of you.²

For finer detail on the early period, see our week-by-week Mounjaro guide and the page on what happens in week 1. If you wonder whether the starter strength does anything, read can you lose weight on 2.5mg Mounjaro.

How your response is reviewed

Treatment response is reviewed by your prescriber: 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 That review is a normal safeguard, not a penalty.

05 · A month of injections

How much weight can I lose in a month with injections?

In the first month the honest answer is: usually not a lot, and it varies. Everyone starts Mounjaro on 2.5mg weekly, and this starting dose is about letting your body adjust, not about weight loss itself.¹ Some people notice appetite change and early loss in week one, others feel little until a higher dose.

Early readings on the scale also include water weight. A big first-week drop can flatten out, and a quiet first month does not mean the medicine is not working.

What a month does tell you is how you tolerate treatment. Mild nausea, altered appetite and tiredness in the first days after each injection are the commonest early effects and usually settle.¹ Our guide to results after one month explores this further.

06 · Belly fat and body changes

Will weight loss injections get rid of belly fat?

Weight loss injections can reduce waist size on average, but fat will not necessarily come off any particular area. In trials, weight loss on tirzepatide came with average improvements in waist size, blood pressure, cholesterol and blood-sugar measures, and most participants with prediabetes returned to normal blood-sugar levels.²

These are trial-average secondary outcomes, not promises. They are why prescribers talk about weight management as health management rather than appearance.

If belly fat is your main concern, the practical points are the same as for any weight goal: stay on the dose your prescriber recommends, keep protein and activity up, and measure your waist as well as weighing yourself. Tape measurements often show progress when the scale stalls.

07 · Plateaus and stalls

What if the scale stops moving?

A stall is normal. Weight loss on Mounjaro is not linear — plateaus of a few weeks are normal and expected as the body adapts to a lower weight.

Within the licence, the responses are:

• Review food intake honestly, because portions drift back up.
• Protect protein and activity.
• Check the basics, such as sleep and alcohol.
• Discuss with your prescriber whether a dose step-up is appropriate if you are not yet at maximum.

A plateau is not a reason to double doses or add unlicensed products. Altering doses outside the licence means unknown dosing accuracy and no safety data.¹

08 · Other weight loss injections

How do other weight loss injections compare?

Mounjaro is not the only licensed injection. Wegovy (semaglutide) is also a weekly injection, with pens of 0.25mg, 0.5mg, 1mg, 1.7mg and 2.4mg; titration steps up after at least four weeks, reaching the 2.4mg maintenance dose from week 17.¹⁸ Liraglutide (Saxenda and similar products) is supplied at 6mg/ml and is a daily injection, unlike the weekly Mounjaro and Wegovy.

Tirzepatide activates two natural gut-hormone receptors at once, GIP and GLP-1, which together help regulate appetite, slow how quickly the stomach empties, and improve the way the body responds to insulin. This dual action is what distinguishes Mounjaro from single-action GLP-1 medicines such as semaglutide.¹

For figures on other products, your prescriber can advise.

Be wary of supplements marketed as natural alternatives to injections. They are low-cost supplements with no clinical oversight, dosing is not standardised, and dramatic weight-loss claims made for them are not backed by licensed-medicine evidence.

09 · Stopping treatment

What happens to your body when you stop Mounjaro?

The medicine clears gradually, and its appetite effect fades with it. 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 As that happens, many people notice hunger returning.

Will you regain weight if you stop? Mounjaro manages weight; it does not cure the biology behind it. 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 treatment lost a further 5.5% on average. Stopping should always be planned with your prescriber, with diet and activity habits ready to carry the load.¹

Do not stop and restart on your own schedule, and do not alter doses outside the licence. If you miss a dose, take it as soon as you can within 4 days (96 hours) of the scheduled time. If more than 4 days have passed, skip the missed dose entirely and take the next one on your normal day — never take two doses within 3 days of each other.¹

10 · What to avoid

What should you avoid while taking Mounjaro?

Avoid anything that undermines the plan or changes the dose outside the licence.

• Do not take extra doses or double up after a plateau.
• Do not add unlicensed products to speed things up.
• Do not rely on the injection alone: it is used alongside a reduced-calorie diet and increased physical activity.
• Review alcohol and sleep honestly, as these are part of the basics.

For anything else, such as foods that upset your stomach or interactions with other medicines, tell the prescriber reviewing you. If you are using the contraceptive pill, switch to a non-oral method or add a barrier method (such as condoms) for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase. Report any new or unexpected symptom to your prescriber, and you can also report side effects through the Yellow Card scheme.¹⁹ 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 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.

11 · NHS and private access

Can you get weight loss injections on the NHS?

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, and the NHS primary-care rollout began in June 2025 with the highest-need groups first (initially BMI 40+ with four or more qualifying conditions).⁴⁶ Full rollout is expected to take years, which is why many people who meet the licensed criteria choose regulated private treatment rather than waiting.

Private treatment is supplied only after an online consultation reviewed by a GPhC-registered prescriber (our registration is GPhC 9012878). Mounjaro is a prescription-only medicine used alongside a reduced-calorie diet and increased physical activity, and individual results vary.