Why does weight loss plateau on Mounjaro or Wegovy?

What is a weight-loss plateau?

It is the point where weight stops falling even though treatment carries on. Every obesity treatment eventually reaches one, a 2024 modelling study says.³

The study is by Kevin Hall at the US National Institutes of Health. It says every intervention "eventually results in a body weight plateau after which no further weight loss occurs".³ Diets usually level off within about 12 months.³ With GLP‑1 medicines, weight loss kept going without an obvious plateau until well after 12 months.³

A 2025 nutrition advisory from four US obesity and nutrition societies describes the usual shape:⁴

• First 6 months: weight falls fastest.⁴
• After that: the loss slows.⁴
• Around 18 months: weight broadly levels off.⁴

These are averages across many people. Some people level off sooner, and some later.

When did weight level off in the Mounjaro and Wegovy trials?

In the two-year Wegovy trial, average weight fell until about week 68, then held steady. In the main Mounjaro trial, people with prediabetes who stayed on for more than three years kept losses close to the 72-week figures.^1,2

How these trials work:

• People are split into groups at random.
• One group gets a dummy injection (placebo) with no medicine in it.
• Everyone gets the same diet and activity advice.
• The gap between the groups is what the medicine added.

Each card is a separate trial. Separate trials can't be compared directly, so read each card on its own.

A worked example. For someone starting at 90 kg (198 lb), the STEP 5 average of 15.2% is about 13.7 kg (30 lb).¹ That is an average, not a promise.

Not everyone loses the same. In STEP 5, 74.7% of people on Wegovy lost at least 5% of their weight, against 37.3% on the dummy.¹ Put the other way, about 25 in 100 on Wegovy lost less than 5%. The 176-week Mounjaro figures come only from the people with prediabetes, so they are a smaller group than the 72-week figures.²

Why does weight stop falling on these medicines?

Weight stops falling because, as you lose weight, appetite rises and you use a little less energy. In time, what you eat and what you use match again.³

Hall used a mathematical model of how the body balances energy. In it, each kilogram lost raised appetite by about 400 kJ (95 kcal) a day, when no treatment was weakening that pull.³ Food intake crept back up until it matched the energy the body was using, and weight levelled off.³

• Semaglutide and tirzepatide weakened this appetite pull by about 40 to 70% in the model.³
• Timing: the model put the plateau at about 24 months for both medicines. Diets usually level off within about 12 months.³
• No wearing off needed: the model reached a plateau with the medicine's effect held constant, and it predicted no regain.³

Hall calls these results preliminary. The model works with group averages and leaves out the large differences between individuals.³

What do the Australian labels say about doses?

Each label sets maintenance doses and a top dose. Moving up a step is a prescriber's decision, made at least 4 weeks after the last change.^1,2

• Mounjaro: the label lists 5 mg, 10 mg and 15 mg as maintenance doses. It says 2.5 mg, 7.5 mg and 12.5 mg are not maintenance doses, and the top dose is 15 mg.²
• Mounjaro steps: after the first 4 weeks at 2.5 mg, the dose can rise in 2.5 mg steps, at least 4 weeks apart, "if needed".²
• Wegovy: the maintenance dose is 2.4 mg, reached over 16 weeks. The label allows 1.7 mg for people who can't tolerate 2.4 mg.¹
• Wegovy 7.2 mg: only for adults whose BMI was 30 or more when they started, after at least 4 weeks on 2.4 mg. If weight doesn't improve further on 7.2 mg, the label says to go back to 2.4 mg.¹

Our post on Wegovy 7.2 mg in Australia covers that dose, its trial and its side effects.

Stopping rules. The Wegovy label says teenagers should stop if their BMI hasn't fallen by at least 5% after 12 weeks on their top dose.¹ We found no similar rule for adults in the Australian Wegovy or Mounjaro labels.

Does a plateau mean the medicine has stopped working?

Withdrawal trials suggest it is still doing work. When people were switched to a dummy injection, weight came back; those who kept taking the medicine kept it off.^1,2

• STEP 4 (Wegovy): after 20 weeks on Wegovy, people were split. Over the next 48 weeks, those who continued lost a further 7.9% of their body weight, while those moved to a dummy regained 6.9%.¹
• SURMOUNT-4 (Mounjaro): after 36 weeks on Mounjaro, people were split. Over the next 52 weeks, those who continued lost a further 6.7% of their body weight, while those moved to a dummy regained 14.8%. For someone weighing 90 kg (198 lb) when the groups were split, that is about 6 kg (13 lb) lost against about 13 kg (29 lb) regained.²

The Australian Obesity Management Algorithm, written by Australian diabetes, obesity and GP bodies, says weight-loss medicines "will usually be required long-term". It adds that data on long-term safety and effectiveness are limited.⁵ Our guide to stopping a GLP‑1 covers what happens after the last dose.

What else matters once weight levels off?

Australia's obesity algorithm calls its weight-loss targets indicative only, and says smaller losses still bring health benefits.⁵

• Targets: the algorithm suggests 10 to 15% for a BMI of 30 to 40, and more than 15% above 40. It says a person and their clinician should set their own target.⁵
• Real life: the 2025 advisory notes loss is often lower outside trials. It gives about 11% at 60 weeks on semaglutide 2.4 mg for people without diabetes.⁴
• Protein: the advisory suggests 80 to 120 g a day; higher targets of 1.2 to 1.6 g per kg have been proposed during weight loss.⁴ For a 90 kg (198 lb) person, 1.2 g per kg is 108 g. If you have kidney disease, ask your doctor first.
• Strength: it suggests strength exercise at least 3 times a week, plus 150 minutes of moderate activity.⁴ The Australian algorithm says resistance exercise can protect muscle.⁵

Questions people ask

How we researched this

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