Mounjaro Weight Loss: What the Trials Found, by Dose and Over Time

Mounjaro (tirzepatide) is licensed in the UK for weight management alongside a reduced-calorie diet and more physical activity. This guide sets out what the main trials found: how much weight people lost at each dose, how results differed with type 2 diabetes, how quickly the effects build and what happened when people stopped. These are trial averages, not a prediction for any one person.

How Much Weight Do People Lose on Mounjaro?

In SURMOUNT-1, average weight change at 72 weeks was -15.0% (5 mg), -19.5% (10 mg) and -20.9% (15 mg).

In SURMOUNT-1, published in the New England Journal of Medicine in 2022, 2,539 adults with obesity, or overweight with a weight-related condition, and without diabetes took tirzepatide 5 mg, 10 mg or 15 mg or a placebo once a week for 72 weeks, alongside diet and activity advice.

Average change in body weight at 72 weeks was -15.0% on 5 mg, -19.5% on 10 mg and -20.9% on 15 mg, against -3.1% on placebo. People started at an average weight of 104.8 kg. Like the SURMOUNT-2 figures below, these averages count everyone who started, including people who stopped treatment.

The trial was funded by Eli Lilly, which makes Mounjaro. Results in everyday use depend on the dose, how long someone stays on treatment and the diet and activity changes that go with it.

Results by Dose

85-91% lost at least 5% of their weight; 50-57% on 10-15 mg lost at least 20%.

SURMOUNT-1 also reported how many people reached different amounts of weight loss at 72 weeks:

• At least 5% of body weight: 85% on 5 mg, 89% on 10 mg and 91% on 15 mg, against 35% on placebo.

• At least 20%: 50% on 10 mg and 57% on 15 mg, against 3% on placebo.

Higher doses led to more weight loss on average, but the step from 10 mg to 15 mg added less than the step from 5 mg to 10 mg, and side effects can limit how high the dose goes. The dose is decided with your prescriber; see Mounjaro dosage.

Weight Loss With Type 2 Diabetes

In SURMOUNT-2, -12.8% (10 mg) and -14.7% (15 mg) at 72 weeks, against -3.2% on placebo.

SURMOUNT-2, published in The Lancet in 2023, tested tirzepatide in 938 adults with obesity or overweight and type 2 diabetes for 72 weeks.

Average change in body weight was -12.8% on 10 mg and -14.7% on 15 mg, against -3.2% on placebo, and 79% to 83% of people on tirzepatide lost at least 5% of their weight, against 32% on placebo.

On average, weight loss was smaller than in SURMOUNT-1, which did not include people with diabetes.

How Quickly Does the Weight Come Off?

Hunger fell from week 1; weight loss started early and continued over 72 weeks.

The UK product information (SmPC) reports that tirzepatide reduced hunger from week 1 and increased fullness from week 3, and that in SURMOUNT-1 weight loss started early and continued throughout the 72 weeks.

Treatment starts on 2.5 mg and the dose goes up in steps at least 4 weeks apart, so the higher doses are reached over several months. See how Mounjaro works and how long it takes.

What Happens If You Stop?

In SURMOUNT-4, switching to placebo led to an average 14.0% regain; continuing gave a further 5.5% loss.

SURMOUNT-4, published in JAMA in 2024, looked at what happens after the first months of treatment. 670 adults who completed 36 weeks on tirzepatide had lost an average of 20.9% of their weight. They were then randomly assigned to keep taking it or switch to a placebo for another 52 weeks:

• People who continued lost a further 5.5% on average.

• People who switched to placebo regained 14.0% on average.

Over the whole 88 weeks, the average loss was 25.3% for those who stayed on tirzepatide and 9.9% for those who stopped. The researchers concluded that stopping led to substantial regain. Talk to your prescriber before stopping; see how to come off Mounjaro.

Is the Weight Lost Mostly Fat?

The SmPC says the weight lost is mostly fat mass.

The SmPC states that the body weight reduction with tirzepatide is mostly due to reduced fat mass, and that reduced food intake contributes to the weight loss. It is licensed for use alongside a reduced-calorie diet and more physical activity.

Mounjaro Compared With Wegovy

In SURMOUNT-5, tirzepatide led to more weight loss than semaglutide.

In SURMOUNT-5, a trial comparing them directly, the Mounjaro SmPC reports that tirzepatide led to a "superior and clinically meaningful reduction in body weight compared to semaglutide". For more on how the two differ, see Mounjaro vs Wegovy.

Why Results Vary, and When Treatment Is Reviewed

Results vary widely; treatment is reviewed if less than 5% is lost 6 months after the highest tolerated dose.

Trial averages hide a wide range. Some people lose much more than the average and some lose less, depending on the dose they reach, side effects, other health conditions and the changes they make to eating and activity.

The SmPC sets a review point: if someone has not lost at least 5% of their starting weight 6 months after reaching their highest tolerated dose, a decision is needed on whether to continue.

Mounjaro is licensed for weight management in adults with a BMI of 30 kg/m² or more, or 27 to 29.9 kg/m² with at least one weight-related condition, and a prescriber checks whether it is suitable.

Side Effects to Expect

Mostly stomach-related, while the dose is increasing; seek urgent help for severe, persistent stomach pain.

The most common side effects are stomach-related, such as nausea, diarrhoea, vomiting and constipation, mostly while the dose is increasing. Seek immediate medical attention for persistent, severe stomach pain, which can be a sign of pancreatitis. See Mounjaro side effects for the full list, and report suspected side effects to the MHRA Yellow Card scheme.

Frequently Asked Questions