Switching from Mounjaro to Wegovy: what to expect

In short

Neither SmPC gives a dose conversion between Mounjaro and Wegovy
Wegovy starts at 0.25mg and rises every 4 weeks through 0.5mg, 1mg and 1.7mg to 2.4mg
Adults with obesity can move from 2.4mg to 7.2mg after at least 4 weeks on 2.4mg
A missed Wegovy dose can be taken up to 5 days late, against 4 days for Mounjaro
In SURMOUNT-5, average weight loss at 72 weeks was 13.7% on semaglutide and 20.2% on tirzepatide
Stop Wegovy at least 2 months before a planned pregnancy, compared with 1 month for Mounjaro

There is no official dose conversion from Mounjaro to Wegovy. The Wegovy licence starts at 0.25mg for 4 weeks and steps up every 4 weeks to a 2.4mg maintenance dose, and most prescribers follow this schedule after a switch. Take your first Wegovy dose on the day your next Mounjaro dose would have been due. While the new dose builds, your appetite may return a little, and some people regain weight before the effect catches up.

Why people move from Mounjaro to Wegovy

People switch for practical and medical reasons:

cost, as private prices for the two medicines differ and change over time
a supply gap in a Mounjaro strength
side effects on Mounjaro they found hard to manage
an NHS service offering semaglutide rather than tirzepatide
a heart health reason, as Wegovy is licensed to reduce cardiovascular risk in adults with established heart or circulation disease and a BMI of 27 or more

If cost is the reason, compare UK Mounjaro prices first. A cheaper Mounjaro supply may suit you better than a change of medicine. If supply is the reason, the guide to Mounjaro supply and shortages covers short-term options, since a gap of a week or two is rarely worth a switch.

Starting dose on Wegovy

The two medicines contain different active ingredients. Mounjaro is tirzepatide, which acts on GIP and GLP-1 receptors. Wegovy is semaglutide, which acts on GLP-1 alone. The milligram doses do not line up, and neither Summary of Product Characteristics (SmPC) gives a conversion.

The Wegovy SmPC sets this schedule:

Weeks	Wegovy dose
1 to 4	0.25mg
5 to 8	0.5mg
9 to 12	1mg
13 to 16	1.7mg
17 onwards	2.4mg maintenance
After at least 4 weeks on 2.4mg	7.2mg, for adults with obesity

Most prescribers start everyone at 0.25mg. Some start at 0.5mg or 1mg for people who were on 10mg or 15mg of Mounjaro and had few side effects. This shortens the time spent on the lowest doses, but it sits outside the licensed schedule, so the decision belongs to your prescriber. If your stomach struggles at any step, the SmPC allows delaying the next increase or dropping back to the previous dose.

When to take your first Wegovy dose

Neither SmPC sets a washout period. The Wegovy SmPC says semaglutide should not be used with any other GLP-1 medicine at the same time. The usual approach:

Take your last Mounjaro dose as normal.
Wait 7 days, until your next injection day.
Take your first Wegovy dose on the same weekday.
Carry on weekly.

Tirzepatide has a half-life of about 5 days, so a small amount remains when you start Wegovy. If you have gone more than 2 weeks without Mounjaro, start Wegovy at 0.25mg. Dispose of leftover Mounjaro pens safely, as the guide to disposing of KwikPens explains. An opened pen lasts only 30 days out of the fridge in any case.

Side effects after the switch

Wegovy and Mounjaro share the same common side effects. In the STEP 1 trial behind the Wegovy licence, nausea affected 43.9% of people on semaglutide 2.4mg against 16.1% on placebo, with diarrhoea in 29.7%, vomiting in 24.5% and constipation in 24.2%. Most of these happened during the dose steps.

Different trials measure side effects in different ways, so these figures are not directly comparable with the Mounjaro trials. The fairest comparison is SURMOUNT-5, a head-to-head trial published in the New England Journal of Medicine in 2025. Overall side effects affected 79% of people on semaglutide and 76.7% on tirzepatide, mostly mild to moderate stomach problems in both groups.

In practice, some people find Wegovy easier and some find it harder. If you left Mounjaro because of side effects, the low Wegovy starting dose gives you the best chance of settling. Eat smaller meals, cut back on fatty and fried food, and sip fluids through the day while each new dose beds in. Severe stomach pain spreading to your back, or vomiting you cannot stop, needs urgent advice on either medicine.

What happens to your weight

Expect a change of pace. In SURMOUNT-5, adults with obesity lost an average of 13.7% of their body weight on semaglutide after 72 weeks, against 20.2% on tirzepatide. In STEP 1, average loss on Wegovy 2.4mg was 14.9% over 68 weeks.

No trial has studied people moving from tirzepatide to semaglutide, so the effect of this switch on weight is not established. During the first 2 to 3 months on 0.25mg to 1mg, your appetite may be stronger than on a high Mounjaro dose, and some people regain a few kilograms. Plan for this:

keep regular meals with protein at each one
weigh yourself weekly rather than daily
tell your prescriber if hunger returns strongly, as they may adjust the pace of dose steps

The 7.2mg dose gives another option. In the STEP UP trial, people on 7.2mg lost an average of 20.7% of their body weight. The guide to which GLP-1 is best for weight loss compares the trial results side by side.

Rules which differ between the two medicines

Check these before your first Wegovy dose, because habits built on Mounjaro may no longer fit.

Rule	Mounjaro	Wegovy
Missed dose window	Up to 4 days late	Up to 5 days late
Minimum gap between doses	3 days	3 days
Stop before planned pregnancy	At least 1 month	At least 2 months
Pill contraception rule	Extra method for 4 weeks after starting and each increase	No equivalent rule in the SmPC
NHS review point	Under 5% loss after 6 months on the highest tolerated dose	Under 5% loss after 6 months

The pill rule for Mounjaro is explained on the contraceptive pill page. Check with your prescriber which rule applies to you once you have switched.

Wegovy on the NHS

NICE TA875 recommends semaglutide on the NHS within specialist weight management services, for a maximum of 2 years. It applies to adults with a BMI of at least 35, or 30 to 34.9 in some cases, plus at least one weight-related condition. The thresholds are usually 2.5 lower for people from some ethnic backgrounds. Tirzepatide has no fixed time limit under NICE TA1026. The Wegovy pill is not available on the NHS.

Switching back

Give Wegovy a fair trial before you decide. The full 2.4mg dose is not reached until week 17, so judging it in the first 2 months tells you little.

If Wegovy does not suit you, a move back to Mounjaro usually means starting at 2.5mg again. The guide to switching from Wegovy to Mounjaro covers the move in detail, including the usual starting dose and timing.

Questions people ask

What dose of Wegovy should I start on after Mounjaro?

The Wegovy licence starts at 0.25mg for 4 weeks, and most prescribers follow this. Some start higher, at 0.5mg or 1mg, for people who were on a high Mounjaro dose and tolerated it well. This is a judgement outside the standard schedule and depends on your history and any gap.

How long after my last Mounjaro injection can I start Wegovy?

Most prescribers advise taking your first Wegovy dose on the day your next Mounjaro dose would have been due, 7 days after your last injection. Neither SmPC sets a formal washout, but the two should not be used together.

Will I regain weight switching from Mounjaro to Wegovy?

Some people do, especially in the first 2 to 3 months while the Wegovy dose builds from 0.25mg. No trial has measured this switch directly. In head-to-head trials semaglutide gave less average weight loss than tirzepatide, so expect a steadier pace rather than faster loss.

Does Wegovy have fewer side effects than Mounjaro?

Not as a rule. Both medicines have the same main stomach side effects, mainly nausea, diarrhoea, vomiting and constipation. In SURMOUNT-5 the overall rate of side effects was 79% on semaglutide and 76.7% on tirzepatide. Some people tolerate one better than the other.

Can I switch back to Mounjaro if Wegovy does not work for me?

Yes, with your prescriber's agreement. The switch back follows the Mounjaro licence, starting at 2.5mg in most cases. Give Wegovy a fair trial first, as the full 2.4mg dose is not reached until week 17.

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: Switching from Mounjaro to Wegovy: what to expect. Site: Mounjaro Info (https://mounjaroinfo.co.uk/guides/switching-from-mounjaro-to-wegovy/). Reviewed 22 October 2026. Topic: Mounjaro (tirzepatide), UK.

There is no official dose conversion from Mounjaro (tirzepatide) to Wegovy (semaglutide). The Wegovy licence starts at 0.25mg and steps up every 4 weeks to a 2.4mg maintenance dose, and most prescribers follow this. Take your first Wegovy dose on the day your next Mounjaro dose would have been due. Expect your appetite to return a little while the new dose builds, and some people regain weight.

Neither SmPC gives a dose conversion between Mounjaro and Wegovy
Wegovy starts at 0.25mg and rises every 4 weeks through 0.5mg, 1mg and 1.7mg to 2.4mg
Adults with obesity can move from 2.4mg to 7.2mg after at least 4 weeks on 2.4mg
A missed Wegovy dose can be taken up to 5 days late, against 4 days for Mounjaro
In SURMOUNT-5, average weight loss at 72 weeks was 13.7% on semaglutide and 20.2% on tirzepatide
Stop Wegovy at least 2 months before a planned pregnancy, compared with 1 month for Mounjaro

Cite as: Mounjaro Info, "Switching from Mounjaro to Wegovy: what to expect", https://mounjaroinfo.co.uk/guides/switching-from-mounjaro-to-wegovy/, reviewed 22 October 2026.