How much weight people lose
In their main trials, adults on the highest dose of Mounjaro lost about 20% of their body weight on average over 72 weeks, compared with about 3% on placebo. On Wegovy 2.4 mg, average loss was about 15% over 68 weeks, compared with about 2% on placebo. Everyone in these trials also followed a reduced-calorie diet and increased their activity.
Averages hide a wide range. Some people lose much more, some much less, and a minority lose very little. How you tolerate the medicine, the dose you reach, and what you eat all play a part.
How quickly it happens
The first weeks are spent on a low starting dose that's there to let your body adjust, so early weight loss is usually modest. Loss tends to pick up as the dose rises over the first few months, and in the trials it was still continuing well past six months before levelling off. Comparing yourself week by week with someone else isn't a useful guide.
The dosing guide explains how the dose steps up.
Why results vary
- The dose you reach, and how long you stay on it
- Side effects that stop you stepping up
- What and how much you eat. The medicine reduces appetite; it doesn't cancel out a high-calorie diet.
- Activity, sleep and alcohol
- Other conditions and medicines, including some that cause weight gain
When weight loss slows down
It's normal for weight loss to slow over time, and for weight to stay flat for a few weeks before moving again. If it has stopped for longer, talk to your prescriber: options include reviewing your dose, your diet, or whether this medicine is the right one for you. Don't increase the dose on your own.
NICE says that if someone has lost less than 5% of their starting weight after 6 months on the highest dose they can tolerate, they and their prescriber should decide together whether to carry on.
What happens when you stop
Most people regain weight after stopping. In SURMOUNT-4, people who had lost about 21% over 36 weeks on tirzepatide were split into two groups. Over the next year, those who kept taking it lost a further 5.5% on average, while those switched to placebo regained 14%.
Semaglutide is similar. In the year after stopping Wegovy in the STEP 1 trial, people regained about two-thirds of the weight they had lost (11.6 of 17.3 percentage points).
That doesn't mean you can never stop. Building eating and activity habits while on treatment helps, and if you want to stop or reduce your dose, plan it with your prescriber.
How long the medicine stays in your body
Both are long-acting, which is why they're taken once a week. Tirzepatide (Mounjaro) has a half-life of about 5 days. Semaglutide (Wegovy) has a half-life of about a week, and after the last 2.4 mg dose it stays in the bloodstream for about 7 weeks.
That's why the medicines have to be stopped well before trying for a baby (at least one month for Mounjaro, two months for Wegovy), and why their effect on appetite fades gradually over the weeks after a last dose rather than stopping overnight.
Maintenance doses
The maintenance dose is the one you stay on once the dose has stopped rising. For Mounjaro, the recommended maintenance doses are 5, 10 or 15 mg a week. For Wegovy it is 2.4 mg a week, reached after about 16 weeks. You don't have to reach the highest dose: if a lower dose is working and you tolerate it, your prescriber can keep you on it.
Diet and activity alongside treatment
Both medicines are licensed for use alongside a reduced-calorie diet and more physical activity, and the trial results above come from people doing both. The medicine makes the diet easier to keep to; it doesn't replace it.
The NHS recommends that adults do at least 150 minutes of moderate activity a week, or 75 minutes of vigorous activity, plus strengthening activities that work all the major muscles on at least 2 days a week. If you're new to exercise, build up gradually.
How long to stay on treatment
There isn't a fixed end date. Treatment is reviewed regularly, and continues while it's working, you tolerate it, and it's still the right choice for you. NHS rules differ: NICE limits NHS semaglutide treatment to 2 years, for example. A private prescription doesn't carry that limit, but your prescriber will still review it.
Related guides
Sources
- Jastreboff AM et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med 2022
- Wilding JPH et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med 2021
- Aronne LJ et al. Continued Treatment With Tirzepatide for Maintenance of Weight Reduction (SURMOUNT-4). JAMA 2024
- Wilding JPH et al. Weight regain after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes Obes Metab 2022
- NICE TA1026: Tirzepatide for managing overweight and obesity
- NICE TA875: Semaglutide for managing overweight and obesity
- Mounjaro KwikPen Summary of Product Characteristics (emc)
- Wegovy FlexTouch Summary of Product Characteristics (emc)
- NHS: Physical activity guidelines for adults aged 19 to 64
General information only. Your results and treatment plan are discussed with your prescriber.
