How Much Weight Can You Lose in One Month on Mounjaro? (October 2026)

01 · The short answer

What can you realistically expect from one month of Mounjaro?

You can realistically expect a gradual start rather than a dramatic drop. Weight loss on Mounjaro is gradual by design, and the first weeks on 2.5mg are an adjustment phase where losses are usually modest.² Some people notice appetite change and early loss in week one; others feel little until a higher dose. Both are normal.

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

02 · What it costs

What does a first month of Mounjaro cost?

A first month uses one 2.5mg pen, which lasts four weeks. Your first 2.5mg pen costs £129.99 with code FIRST40 (standard price £169.99), and every later order is £25 off the standard price (code DOSE25). You can see current doses and prices on the Mounjaro pen page, and all six strengths are in stock.

Planning beyond month one matters, because one month is a starting point, not a course. The first four pens (2.5mg, 5mg, 7.5mg and 10mg) cost £959.96 at standard prices. A first year (13 pens) costs £2,711.88 if you settle at 5mg, up to £3,599.88 at 15mg. A new customer's first order is £40 less and every later order £25 less than those standard figures. At 7.5mg a pen is £279.99, at 10mg £290.99 and at 12.5mg £319.99.

03 · Getting started

Who can start, and how does ordering work?

Mounjaro is licensed for adults with a BMI of 30 or above, or a BMI 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 with a reduced-calorie diet and increased activity, and a prescriber assesses your BMI, history and current medicines first.¹

On the NHS, Mounjaro is available 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 primary-care rollout began in June 2025 with the highest-need groups first.⁴⁶ Many people who meet the licensed criteria choose regulated private treatment rather than wait.

Ordering with us takes three steps:

• Complete the free online consultation, a short health questionnaire with no charge and no obligation.
• A GPhC-registered prescriber reviews it. Payment is taken when you place the order; if the prescriber decides the treatment is not suitable, the order is refunded automatically in full.
• We dispense and dispatch from our registered pharmacy (same-day dispatch when ordered by 3pm), with free next-day tracked delivery in temperature-controlled packaging. Needles, a sharps bin and injection guidance come with every order.

Our Mounjaro comes through official LillyDirect supply, direct from Eli Lilly's UK distribution, as genuine KwikPens. Ongoing monthly reviews are included, and you can browse all weight loss treatments if you want to compare options.

04 · Month one explained

What actually happens in month one on Mounjaro

Month one is the start of a gradual process, not the point where most of the change happens. Mounjaro is the brand name for tirzepatide, a once-weekly injection made by Eli Lilly, supplied as a pre-filled multi-dose KwikPen in six strengths from 2.5mg to 15mg.¹ Treatment begins on the lowest strength, the 2.5mg pen, so the opening weeks are about letting your body adjust.

The first weeks on 2.5mg are an adjustment phase and losses are usually modest.² That is deliberate: the medicine is introduced at a low strength and stepped up. Most measurable progress builds from 5mg onward, month by month. If you hoped a single month would show the result of the whole treatment, it is better to reset that expectation now.

Experiences differ widely. Some people notice a change in appetite and early loss in week one. Others feel little until they move to a higher dose. Neither pattern is a sign that the medicine is or is not working for you. A quieter first month does not predict a poor outcome.

How does it work? 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. In practice most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet.¹ The medicine makes the diet easier to follow; it does not replace it.

Our guide to Mounjaro before and after one month covers this stage in more detail. And if you are wondering about the very first days, see week one on Mounjaro. The point to hold on to is simple: think in months, not days, and judge progress by trend rather than individual weigh-ins.

05 · What the trials measured

What the SURMOUNT-1 trial did and did not measure

The main trial evidence measured weight at 72 weeks, which is far longer than a month. 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 These are trial averages, and individual results vary.

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

To make the percentages concrete, here is a worked example. For someone starting at 100 kg, 15% is about 15 kg, 19.5% is about 19.5 kg and 20.9% is about 21 kg. Those are 72-week trial averages for that starting weight, not a monthly pace.

Why does this matter for a one-month question? The trial figures do not support a specific first-month number. What they support is a direction: loss builds with time and dose. In SURMOUNT-1, average weight loss built month by month, with the full averages measured at 72 weeks.

Also remember who was in the trial. Participants were taking the medicine alongside a reduced-calorie diet and increased physical activity, and the comparison group made lifestyle changes alone. Your own result depends on your starting weight, your dose, how well you tolerate it, and how consistently you support it with food and activity.

06 · Water weight and weigh-ins

Why early loss includes water and weigh-ins mislead

Early weight loss includes water weight, so a single weigh-in tells you very little. That is a feature of the first weeks on any reduced-calorie plan, and it applies here too: the trend over weeks matters more than any one reading.

Practical habits make the trend easier to read. Weigh yourself at the same time of day, under similar conditions, and look at the direction across several weeks rather than day to day. A reading that is up a little after a salty meal or down a little after a poor night is noise, not information. Because the trials measured results at 72 weeks, the sensible frame is months, not days.²

If you are tracking, you might also note things the scales miss: how full you feel after meals, how often you snack between meals, and how your clothes fit. Our free companion app, GLPTrackr (iOS and Android), is designed for tracking a GLP-1 journey, which can help you see the trend rather than the daily wobble.

It is also worth knowing that some people see the scale move early and then stall, while others see little for weeks and then a steady decline. Both fit the pattern described in the evidence: some people notice early loss in week one, others feel little until a higher dose, and both are normal.²

What about the question of whether you can lose weight in just a week? It is possible to see a change, but a week is too short to tell you anything about how the treatment is working. We cover that separately in our one-week guide. Treat any number from the first seven to ten days as a data point, not a verdict, and wait for several weeks of readings before drawing a conclusion about whether it is working for you.

07 · Month one to month three

How progress builds from month one to month three

Progress builds as the dose rises, so month three looks different from month one. 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 12.² A sensible three-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. Our week-by-week guide sets out how this unfolds in more detail.

If you are weighing up whether it is worth starting for only a month, read whether one month of Mounjaro helps. The short version is that one month is a first step. The treatment is designed to be used over a longer period, with your prescriber reviewing your response along the way. After a final dose, tirzepatide has a half-life of about five days, so it takes roughly 4–5 weeks to clear the system, and there is no way to speed this up.¹ That tells you the medicine is not something that switches on and off within days.

08 · Supporting your progress

What you can do to support loss in the first month

The most useful things you can do are the ones the licence is built on: a reduced-calorie diet and increased physical activity. Mounjaro must be used alongside both, and the trial results were achieved with them in place.¹

Because tirzepatide makes you feel fuller sooner and less hungry between meals, it can be easier to eat less. Make that count. Review your food intake honestly, because portions drift back up over time. Protect protein and keep active. Check the basics too: sleep and alcohol both affect how well a plan holds together.

What about "speeding it up"? There is no licensed way to make month one produce more than the starting dose allows. The dose is stepped up by your prescriber, not by you. Taking extra doses, doubling a dose or adding unlicensed products is not appropriate.

Many people ask about foods to avoid, the best time to inject and tips and tricks. No food is banned on Mounjaro. Prioritise protein at each meal, vegetables and fibre, and regular fluids, and choose smaller, slower meals. There is no "best" time of day to inject; Mounjaro works the same morning or evening, and what matters is the same day each week.

On alcohol, the sensible approach is to treat it as part of reviewing your basics: it counts towards your intake and can affect sleep, so discuss your own situation with your prescriber, especially if you have side effects such as nausea.

For wider habits that support a month of effort, our blog on losing belly fat in a month safely is a useful companion read.

09 · Plateaus and slow weeks

What to do if the scale stalls

A stall is normal and does not mean the treatment has stopped working. 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 practical and in order:

• Review your food intake honestly, since portions drift back up.
• Protect protein and activity.
• Check the basics, including 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. Doing so adds risk without a supported benefit. If you are still on the starting pen, the most likely explanation for a quiet few weeks is simply that you are on the lowest strength, and the dose you respond to may still be ahead of you.

Treatment response is formally reviewed too. 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.² For someone starting at 100 kg, 5% is about 5 kg.

Repeat orders re-check your suitability, there is no auto-shipping, and the prescribing team handles dose titration and follow-up assessments, so you are not left guessing whether a slow month is normal.

If you want a month-by-month sense of what "slow" can look like, the guide to one-month loss explains why individual months differ so much.

10 · Early side effects

Early side effects: what is normal in the first weeks

The commonest early effects are mild and usually settle. Mild nausea, altered appetite and tiredness in the first days after each injection are the commonest early effects.¹³ Many people find these ease as the weeks go on.

Why mention this on a page about weight? Because side effects shape how well people stick to a plan in month one. If nausea makes you want to avoid food altogether, say so to your prescriber rather than pushing on alone. Your reduced-calorie diet still needs to be a balanced one, and support is part of what monthly reviews are for.

Most side effects are digestive: the most common, affecting more than 1 in 10 people, are nausea, diarrhoea, vomiting, constipation and abdominal discomfort, and for most people they ease within days to a few weeks as the body adjusts. If you notice a new symptom, discuss it with your prescriber. You can also report suspected side effects through the MHRA Yellow Card scheme.¹⁹

One interaction is worth knowing about from the outset: Mounjaro can reduce absorption of oral contraceptives because stomach emptying slows. 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 If you use one, speak to your prescriber about this before you start.⁷ If you take insulin or sulfonylureas, doses may need adjusting because of the risk of low blood sugar, so tell your prescriber about every medicine you take.

When buying, use a regulated pharmacy. Counterfeit weight-loss pens exist, and anyone offering to supply without a consultation or prescription should be avoided. You can check our registration (GPhC 9012878) on the GPhC register. Our pens are genuine KwikPens from official LillyDirect supply.⁷

11 · Beyond the scales

Beyond the scales: why one month undersells the treatment

Weight is only one of the outcomes that matter, and most of the others also take longer than a month. 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.

These are trial-average secondary outcomes, not promises. But they explain why prescribers talk about weight management as health management rather than appearance, and why a modest first month is not a failure. It is one early data point in a longer course.

It also helps to think about what a first month can and cannot tell you. It can tell you how you tolerate the medicine, how your appetite responds and whether you can build a routine around a weekly injection. It cannot tell you how much you will lose over a year, and it cannot tell you which dose you will end up on. Those questions are answered over months, with your prescriber reviewing your response.

Dose matters because the trial averages differ by strength. That scaling is why the starting pen is a gentle introduction rather than the full effect.

If you decide to begin, the practical next step is the free consultation. A GPhC-registered prescriber will check whether Mounjaro is suitable for you, and if it is, your first 2.5mg pen costs £129.99 with code FIRST40 (standard price £169.99). Payment options include Visa, Mastercard, Klarna and pay-monthly plans, with no subscriptions.

Mounjaro (tirzepatide) 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.

12 · 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