What to expect, and what happens next.

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 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

• Side effects, and what to do about them
• Eating normally on Mounjaro
• Mounjaro and Wegovy compared