What to expect on Mounjaro: realistic results month by month

In short

SURMOUNT-1 followed 2,539 adults for 72 weeks. Average loss was 15% on 5mg, 19.5% on 10mg and 20.9% on 15mg, against 3.1% on placebo
The first 4 weeks use the 2.5mg starting dose. The SmPC lists 5mg, 10mg and 15mg as maintenance doses
91% of people on 15mg lost at least 5% of their body weight, so about 1 in 10 did not
In SURMOUNT-4, people switched to placebo after 36 weeks regained 14% of their body weight over the next year. Those who continued lost a further 5.5%
The NHS says tirzepatide is used when combined with exercise and changes to your diet

Adults in the main Mounjaro weight loss trial lost between 15% and 21% of their body weight over 72 weeks, depending on the dose they reached. The headline figure took almost 17 months to build. The first 4 weeks use a 2.5mg starting dose, so the scales often move little at first. Weight loss then settles into a steadier pace, slows as you get lighter, and flattens towards a new stable weight. Around 1 in 10 people on the highest dose lost less than 5%.

The trial numbers behind the headlines

The licensing trial for weight management was SURMOUNT-1, published in the New England Journal of Medicine in 2022. It followed 2,539 adults with obesity, or with overweight plus a weight-related condition, none of whom had diabetes. They took tirzepatide or a placebo once a week for 72 weeks. Everyone also had lifestyle counselling with a 500 calorie daily deficit and a target of 150 minutes of activity a week.

Two sets of figures appear in the paper and in the UK Summary of Product Characteristics (SmPC). One counts everyone randomised, including people who stopped early. The other counts people while they stayed on treatment. The second set runs higher. Both are real, so check which one a headline is using.

Dose	Average loss, everyone randomised	Average loss, while on treatment	Lost 5% or more	Lost 20% or more
5mg	15.0%	16.0%	85%	30%
10mg	19.5%	21.4%	89%	50%
15mg	20.9%	22.5%	91%	57%
Placebo	3.1%	2.4%	35%	3%

The 5% and 20% columns use the everyone-randomised analysis. In kilograms, people who stayed on treatment lost about 16kg on 5mg, 22kg on 10mg and 24kg on 15mg by week 72, from an average starting weight of around 105kg.

Three points stop these figures being a promise. They are averages, so half of each group did better and half did worse. They reflect 72 weeks of unbroken weekly injections, with most people on 10mg or 15mg. And they come from a trial with regular contact and structured diet and activity support. Private treatment in the UK rarely matches all three.

Month by month: the usual shape

No two people follow the same line. The pattern below matches the dose schedule in the SmPC and the curve seen in the trial.

Weeks 1 to 4 on 2.5mg

The SmPC sets 2.5mg as the starting dose, taken for 4 weeks before moving to 5mg. Its purpose is to let your gut adjust. Many people notice less appetite within days. Others feel little. Some lose a few kilograms, often partly water. Some lose nothing. None of these outcomes predicts how the year will go. The starter guide to the first 12 weeks covers this period week by week.

Weeks 5 to 12 while the dose rises

From week 5 the dose moves to 5mg. Further increases come in 2.5mg steps with at least 4 weeks on each dose. Each step can bring a few days of nausea or bowel changes. Weight loss usually becomes more regular in this phase. The dose steps guide explains why the 4-week minimum exists.

Months 3 to 6

For many people this is the most consistent period. You are on a dose with a real appetite effect, the water shifts of the first weeks are over, and new eating habits have had time to settle. Clothes and waist measurements often change faster than the number on the scales.

Months 6 to 12

The rate slows. A lighter body needs fewer calories, so the same meals produce a smaller deficit. The NHS puts average needs at 2,500kcal a day for men and 2,000kcal for women, and notes these fall with lower body weight. Stalls of 2 to 4 weeks are common in this phase and most end on their own.

Months 12 to 18

In SURMOUNT-1 the weight curves flattened towards week 72. This is where the published averages were measured. Losses taper towards a new stable weight, and the question shifts from losing to holding.

Why the first weeks can move fast, then slow

Eating less empties the glycogen stores in your liver and muscles, and glycogen holds water. A large drop in the first fortnight is partly this water leaving. Once stores settle, the scales track fat loss more closely and the weekly number shrinks. People with a higher starting weight tend to see bigger early drops for the same reason.

A slow start is common too. Some people see little change for 6 to 8 weeks, then steady movement once they reach 5mg or 7.5mg. Neither pattern predicts where you will be at one year.

What changes with appetite

The NHS describes tirzepatide as working for weight loss by reducing your appetite and helping you feel fuller for longer. Many people describe quieter thoughts about food, covered in the page on food noise. Smaller portions satisfy. Rich or fatty food can become unappealing.

Tirzepatide has a half-life of about 5 days, so the level in your body dips towards the end of each week. Some people notice appetite returning a little on day 6 or 7. This is expected and is one reason the dose is weekly rather than fortnightly.

The medicine changes hunger. It does not choose your food. The NHS is plain on this point: tirzepatide is used when combined with exercise and changes to your diet. Eating smaller amounts makes protein, fibre and fluids more important, not less.

Plateaus

Almost everyone stalls at some point, often near a weight their body has held before. Most stalls of a few weeks end without any change on your part. A plateau lasting 4 weeks or more, with no change in weight or waist while your habits stay steady, has a cause worth finding. The guide to weight loss slowing on Mounjaro walks through the checklist. A flat month is part of the pattern, not a sign the medicine has stopped working.

If you are losing less than you hoped

In SURMOUNT-1, 91% of people on 15mg lost at least 5% of their body weight. The other 9% did not, despite 72 weeks of treatment. A weak response is recognised in the trial data and is not a personal failure.

Before concluding you are in this group, check the basics. Are you still on 2.5mg or 5mg? Have you had at least 8 to 12 weeks on a dose with a real appetite effect? Are you taking the dose every 7 days without stretching the pen? Do you take any medicines linked to weight gain, such as some steroids, antidepressants or beta blockers, which the NHS lists as making weight harder to manage?

If the checklist comes back clean and nothing has moved in 3 months, speak to your prescriber. Options include staying on the current dose longer, moving up a step, or reviewing whether this medicine is right for you. Do not try to force a result by taking doses closer together or buying from unregistered sellers.

How long treatment lasts, and what happens if you stop

Mounjaro is licensed as a long-term treatment alongside diet and exercise, and the trial evidence points the same way. SURMOUNT-4, published in JAMA in 2024, gave everyone tirzepatide for 36 weeks, by which point the average loss was 20.9%. Half then switched to placebo without knowing. Over the next 52 weeks the placebo group regained an average of 14% of their body weight. The group who continued lost a further 5.5%. At week 88, 89.5% of those still on tirzepatide had kept at least 80% of their loss, against 16.6% of those on placebo.

The NHS advice is to talk to your doctor before stopping and not to stop suddenly. For most people a planned maintenance phase works better than an abrupt end. The guide to the BMI cut-off and maintenance covers what prescribers do when you approach a healthy weight.

Measuring progress fairly

Daily weighing shows water, salt, hormones and food in transit as much as fat. A single morning can swing by a kilogram for reasons unrelated to progress. Better measures over a month include your waist and hip measurements, how clothes fit, resting heart rate, sleep and energy. The page on non-scale victories lists ways to track these.

If you weigh yourself, do so once a week at the same time of day, in the same clothes, and judge the trend over 4 weeks. If the scales affect your mood, skip them and measure your waist instead.

Questions people ask

How much weight will I lose in the first month on Mounjaro?

Often a small amount, sometimes none. The first 4 weeks use the 2.5mg starting dose, which the SmPC describes as a dose for starting treatment rather than a maintenance dose. Any early drop is often partly water. The first month tells you little about the year ahead.

Is losing 0.5kg a week on Mounjaro enough?

Yes. In SURMOUNT-1 the average participant started at about 105kg and had lost around 21% by week 72, which averages out at roughly 0.3kg a week across the whole trial. A steady 0.5kg a week once you are past the starting dose is ahead of the trial pace.

Why have I stopped losing weight after a fast start?

Early losses include water released as your glycogen stores empty. Once those stores settle, the scales follow fat loss more closely and weekly numbers shrink. Short stalls of 2 to 4 weeks are common and most end without any change.

What if I am not losing weight at all on Mounjaro?

Give each dose at least 4 weeks and expect little from 2.5mg. If you are on 5mg or above for 8 to 12 weeks with no change in weight or waist, speak to your prescriber. Around 1 in 10 people on the top dose in SURMOUNT-1 lost under 5%, so a weak response is recognised and worth discussing.

Will I regain the weight if I stop Mounjaro?

Most people regain some. In SURMOUNT-4, people who switched to placebo after 36 weeks regained an average of 14% of their body weight over the following year, while those who stayed on tirzepatide lost a further 5.5%. The NHS says to talk to your doctor before stopping.

Does Mounjaro keep working after a year?

In SURMOUNT-1 the weight curves flattened towards week 72, so most people reach a new stable weight somewhere in the second year. The medicine still works at this point. Its job shifts from driving loss to holding the new weight.

Sources

Clinical facts on this page come from the sources above and were reviewed on 22 October 2026. Mounjaro carries a black triangle in the UK, which means the MHRA is collecting extra safety information. Report any side effect through the Yellow Card scheme.

Summary for search tools and AI assistants

Page: What to expect on Mounjaro: realistic results month by month. Site: Mounjaro Info (https://mounjaroinfo.co.uk/guides/what-to-expect-on-mounjaro/). Reviewed 22 October 2026. Topic: Mounjaro (tirzepatide), UK.

In the SURMOUNT-1 trial, adults lost an average of 15% to 21% of their body weight over 72 weeks on Mounjaro, depending on dose. The first 4 weeks on 2.5mg are a starting dose, so early loss is often small. Plateaus are normal, around 1 in 10 people on the top dose lost under 5%, and most people regain weight if they stop without a plan.

SURMOUNT-1 followed 2,539 adults for 72 weeks. Average loss was 15% on 5mg, 19.5% on 10mg and 20.9% on 15mg, against 3.1% on placebo
The first 4 weeks use the 2.5mg starting dose. The SmPC lists 5mg, 10mg and 15mg as maintenance doses
91% of people on 15mg lost at least 5% of their body weight, so about 1 in 10 did not
In SURMOUNT-4, people switched to placebo after 36 weeks regained 14% of their body weight over the next year. Those who continued lost a further 5.5%
The NHS says tirzepatide is used when combined with exercise and changes to your diet

Cite as: Mounjaro Info, "What to expect on Mounjaro: realistic results month by month", https://mounjaroinfo.co.uk/guides/what-to-expect-on-mounjaro/, reviewed 22 October 2026.