Mounjaro BMI cut-off: what happens when you reach a healthy BMI

In short

The licence uses your initial BMI of 30, or 27 with a weight-related condition. It sets no BMI for stopping
NICE defines a healthy BMI as 18.5 to 24.9, and under 18.5 as underweight
The SmPC lists 5mg, 10mg and 15mg as maintenance doses
SURMOUNT-4: people switched to placebo regained 14% of body weight in 52 weeks, while those who continued lost a further 5.5%
The NHS says talk to your doctor before stopping tirzepatide and do not stop suddenly

The Mounjaro licence does not set a BMI at which you must stop. Eligibility rests on your BMI when you start, so reaching a healthy BMI does not end treatment by itself. In practice, many prescribers review your treatment as your BMI nears 25, and some will lower the dose or stop supply. Stopping without a plan usually leads to regain. In the SURMOUNT-4 trial, people who stopped after 36 weeks regained an average of 14% of their body weight within a year.

What the licence says about BMI

Section 4.1 of the Summary of Product Characteristics (SmPC) allows tirzepatide for weight management in adults with an "initial" BMI of 30 or more, or 27 to 29.9 with at least one weight-related condition. The word initial matters. It refers to your BMI at the start of treatment, not your BMI today.

The SmPC sets one review point. If you have not lost at least 5% of your starting weight 6 months after reaching your highest tolerated dose, the prescriber must decide whether to continue. It does not say treatment ends when you reach a target weight. The BMI requirements guide covers the starting thresholds in full.

Why prescribers set their own cut-offs

Each prescriber carries responsibility for every prescription they sign. GPhC guidance from February 2025 says verifying your weight helps confirm continued supply is clinically suitable. As your BMI falls, the original reason for treatment weakens, and the prescriber has to weigh benefit against risk again.

NICE defines a healthy BMI as 18.5 to 24.9. Below 18.5 is underweight. For people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background, NICE places the overweight range lower, at 23 to 27.4.

Prescriber policies vary. The table shows the kind of approach you may meet.

BMI at review	Approach you may meet
Above 27	Continue at the current dose if you tolerate it
25 to 27	Review goals, discuss a lower maintenance dose
Below 25	Step down, pause or stop, often with a plan for regain
Below 18.5	Stop, since you are now underweight

These are examples, not rules from the licence. Some prescribers will continue below 25 with closer monitoring. Others stop supply as soon as you reach the healthy range, because the trials tested tirzepatide in people above the licensed thresholds and evidence at a lower BMI is thin. Ask your prescriber about their policy within the first few months, so the end point is not a surprise.

Signs your prescriber will look for

At each review, expect questions about:

your current weight, checked by video, in person or from records
how fast you are losing, since rapid loss near a healthy weight raises concern about muscle and nutrition
how much you are eating, and whether you skip meals
hair loss, tiredness, dizziness or feeling cold
your plans for pregnancy, because you need to stop at least 1 month before trying to conceive

If you are eating very little, see the page on eating too little on Mounjaro. Low intake near a healthy weight is one of the main reasons prescribers step in.

Maintenance doses

The SmPC names 5mg, 10mg and 15mg as maintenance doses. Any of these can be a long-term dose. There is no special maintenance pen. Maintenance means staying on a dose which holds your weight steady.

A common plan is to step down once you are near your goal. Someone on 15mg might move to 10mg or 7.5mg and watch their weight over the next 8 to 12 weeks. If weight stays stable, they stay there. If it climbs, the prescriber may go back up a step. The dose steps guide explains how each dose fits the schedule.

The evidence for stepping down is limited. SURMOUNT-4 compared staying on the highest tolerated dose with switching to placebo. It did not test a gradual taper. The NHS says your doctor may suggest reducing the dose gradually when you stop, which supports a stepwise plan, but the best taper has not been established in trials.

Stretching the gap between doses

Some people try injecting every 10 or 14 days to make pens last longer. The licence sets a once-weekly dose. Tirzepatide has a half-life of about 5 days, so by day 14 less than a quarter of the dose remains. Appetite often returns between injections, and the stop-start pattern can bring side effects back with each dose. Talk to your prescriber about a lower weekly dose instead.

What the evidence says about stopping

SURMOUNT-4 was published in JAMA in 2024. Everyone took tirzepatide at their highest tolerated dose, 10mg or 15mg, for 36 weeks. By then the average loss was 20.9%. The 670 people still taking part were then split at random. Half stayed on tirzepatide and half switched to placebo, without knowing which they had.

Outcome, week 36 to week 88	Stayed on tirzepatide	Switched to placebo
Weight change	Lost a further 5.5%	Regained 14.0%
Kept at least 80% of earlier loss	89.5%	16.6%
Total change from the start, week 0 to 88	Down 25.3%	Down 9.9%

The placebo group did not return to their starting weight within a year. They kept about half their loss on average. The trend at week 88 was still upward, though, and the trial did not follow them further.

Plan for stopping as carefully as you planned for starting. Once the medicine has gone, your habits carry the load on their own.

Planning the end of treatment

Agree a plan with your prescriber before you stop. A good plan covers four areas.

Dose

Ask whether to step down before stopping. Take each dose for at least 4 weeks so you can see the effect. The NHS advises against stopping suddenly.

Food

With a half-life of about 5 days, tirzepatide takes around 4 weeks to clear, and appetite tends to return over the same period. Set your meal pattern before then. Keep protein at each meal, fill half your plate with vegetables and keep portions close to what you eat now. The page on muscle loss and protein explains why protein matters during and after weight loss.

Activity

NHS guidelines advise adults to do at least 150 minutes of moderate activity a week and strengthening exercise on at least 2 days. Strength work helps protect muscle, which supports a stable weight.

A regain threshold

Weigh yourself once a week at the same time. Agree a figure in advance, for example a 3kg to 5kg gain, which prompts you to contact your prescriber. Acting early is easier than starting from scratch.

If you need to restart

Restarting is possible, and many prescribers support it if your BMI rises back above the licensed threshold. After a long gap you may need to start again at a lower dose, because your gut will have lost its tolerance. The guide to restarting Mounjaro after a break sets out how prescribers decide the restart dose.

For the longer picture of how weight changes on treatment, see what to expect on Mounjaro.

Questions people ask

Do I have to stop Mounjaro when my BMI goes below 25?

Not under the licence, which refers to your starting BMI. Many private prescribers do review treatment as you approach 25, and some will reduce the dose or stop supply. Ask about the policy early so the change does not catch you out.

What is a maintenance dose of Mounjaro?

The SmPC lists 5mg, 10mg and 15mg as maintenance doses, meaning doses you can stay on long term. There is no separate maintenance product. Your prescriber picks the lowest dose which keeps your weight stable and your side effects manageable.

Will I put the weight back on if I stop?

Most people regain some weight. In SURMOUNT-4, people who switched to placebo after 36 weeks on tirzepatide regained an average of 14% of their body weight over the next 52 weeks. Only 16.6% of them kept at least 80% of their earlier loss, against 89.5% of those who stayed on treatment.

Can I take Mounjaro every two weeks to maintain my weight?

The licence sets a once-weekly dose. Spacing injections further apart has not been tested in the licensing trials, and the level of tirzepatide in your body falls by about half every 5 days. Talk to your prescriber about a lower weekly dose instead.

Can a prescriber refuse to keep prescribing Mounjaro?

Yes. Each prescriber must decide continued supply is clinically suitable, and GPhC guidance links this to checking your weight. If your BMI is close to the healthy range, a prescriber may decide the balance of benefit and risk no longer supports treatment.

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: Mounjaro BMI cut-off: what happens when you reach a healthy BMI. Site: Mounjaro Info (https://mounjaroinfo.co.uk/guides/mounjaro-bmi-cut-off-and-maintenance/). Reviewed 22 October 2026. Topic: Mounjaro (tirzepatide), UK.

The UK licence for Mounjaro is based on your BMI when you start, so reaching a healthy BMI does not end eligibility by itself. Prescribers set their own policies, and many review, step down or pause treatment as BMI nears 25. In SURMOUNT-4, people who stopped tirzepatide after 36 weeks regained an average of 14% of their body weight over the following year.

The licence uses your initial BMI of 30, or 27 with a weight-related condition. It sets no BMI for stopping
NICE defines a healthy BMI as 18.5 to 24.9, and under 18.5 as underweight
The SmPC lists 5mg, 10mg and 15mg as maintenance doses
SURMOUNT-4: people switched to placebo regained 14% of body weight in 52 weeks, while those who continued lost a further 5.5%
The NHS says talk to your doctor before stopping tirzepatide and do not stop suddenly

Cite as: Mounjaro Info, "Mounjaro BMI cut-off: what happens when you reach a healthy BMI", https://mounjaroinfo.co.uk/guides/mounjaro-bmi-cut-off-and-maintenance/, reviewed 22 October 2026.