Switching from Wegovy to Mounjaro: how prescribers do it

In short

Neither the Wegovy nor the Mounjaro SmPC gives a dose conversion between the two medicines
The Mounjaro SmPC sets a 2.5mg starting dose for 4 weeks, then 2.5mg steps with at least 4 weeks on each
The Wegovy SmPC advises against using semaglutide with any other GLP-1 medicine at the same time
The usual gap is 7 days: your first Mounjaro dose replaces your next Wegovy dose
In SURMOUNT-5, average weight loss at 72 weeks was 20.2% on tirzepatide and 13.7% on semaglutide

There is no official dose conversion from Wegovy to Mounjaro. The Mounjaro licence starts everyone at 2.5mg for 4 weeks, and most prescribers follow this even if you were on a high Wegovy dose. Some start at 5mg for people who tolerated 1.7mg or 2.4mg of Wegovy well. The usual timing is simple: take your first Mounjaro injection on the day your next Wegovy dose would have been due, and never use both in the same week.

Why there is no conversion table

Wegovy contains semaglutide, which acts on one hormone receptor, GLP-1. Mounjaro contains tirzepatide, which acts on two, GIP and GLP-1. The milligram doses are not comparable, and neither medicine's Summary of Product Characteristics (SmPC) gives a way to convert one to the other.

You may see conversion charts online, often matching 2.4mg of Wegovy to 7.5mg or 10mg of Mounjaro. These are informal guides drawn up by individual services. They are not part of either licence, and no UK regulator publishes one.

The starting dose most prescribers use

The Mounjaro SmPC says the starting dose is 2.5mg once a week. After 4 weeks the dose moves to 5mg, and further increases come in 2.5mg steps with at least 4 weeks on each. Following this schedule is the licensed approach, and many prescribers apply it to everyone switching.

Your Wegovy dose	Common Mounjaro starting dose	Notes
0.25mg to 1mg	2.5mg	Standard licensed start
1.7mg or 2.4mg, tolerated well	2.5mg, or 5mg at some services	5mg is a prescriber judgement outside the standard schedule
Any dose, with ongoing side effects	2.5mg	Gives your gut time to adjust
Any dose, after a gap of more than 2 weeks	2.5mg	Tolerance fades during a break

Starting at 2.5mg can feel like a step back. Your appetite may return a little for the first few weeks, because 2.5mg is a starting dose rather than a maintenance dose. The trade-off is fewer side effects while your body meets a new medicine. The dose steps guide shows how the strengths build.

When to take your first Mounjaro dose

Neither SmPC sets a formal washout period between the two medicines. The Wegovy SmPC does say semaglutide should not be used together with any other GLP-1 medicine. In practice, prescribers usually advise:

Take your last Wegovy dose as normal.
Wait 7 days, so your first Mounjaro dose falls on your usual injection day.
Take 2.5mg of Mounjaro, or the dose your prescriber agreed, on that day.
Carry on weekly from there.

Semaglutide has a half-life of about a week, so some of it remains in your body when you start Mounjaro. This overlap is one reason the low starting dose matters. If you are still having side effects from Wegovy, your prescriber may suggest waiting longer before the first Mounjaro dose.

If you have already gone more than 2 weeks without Wegovy, start Mounjaro at 2.5mg. Do not use up leftover Wegovy pens after you switch.

Side effects when you switch

Wegovy and Mounjaro share the same main side effects: nausea, diarrhoea, constipation, vomiting, indigestion and tiredness. Even if these settled on Wegovy, many people notice them again in the first weeks of Mounjaro and after each step up.

Ways to keep them down:

eat smaller meals and stop when you feel full
cut back on fatty, fried and very sweet food
drink fluids through the day
stay on a dose for longer than 4 weeks if side effects have not settled

Severe stomach pain spreading to your back, vomiting you cannot stop, or signs of dehydration need urgent advice. The page on nausea and vomiting explains what is normal and what is not.

Contraception and pregnancy after the switch

Mounjaro has a specific rule on the pill. If you take an oral contraceptive, use a barrier method as well, or switch to a non-oral method, for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase. The contraceptive pill page explains why.

Both medicines must be stopped before a planned pregnancy. The Wegovy SmPC says to stop semaglutide at least 2 months before. The Mounjaro SmPC says to stop tirzepatide at least 1 month before.

Why people switch

The most common reasons are:

weight loss has slowed or stopped on the top Wegovy dose
side effects on Wegovy were hard to live with
supply problems with a Wegovy strength
a prescriber or NHS service offers Mounjaro instead

The best direct evidence on effect comes from SURMOUNT-5, published in the New England Journal of Medicine in 2025. It compared the two medicines head to head in adults with obesity and without diabetes, each at the highest tolerated dose. After 72 weeks, average weight loss was 20.2% on tirzepatide and 13.7% on semaglutide. Waist size fell by 18.4cm and 13cm. Around 48% of people on tirzepatide lost a fifth or more of their body weight, against 27% on semaglutide. These are averages. Some people do better on semaglutide, and a move to Mounjaro is not a guarantee of faster loss. The guide to which GLP-1 is best for weight loss compares the medicines in more detail.

If Mounjaro does not suit you

Some people find Mounjaro harder to tolerate than Wegovy, or see no extra benefit after several months. Moving back is possible. The Wegovy SmPC also starts at its lowest dose, 0.25mg, and a return to Wegovy uses the same 7-day timing. Give Mounjaro a fair trial first. The SmPC asks for at least 4 weeks on each dose, so judging it before you reach 5mg or 7.5mg is too early.

What to tell your prescriber

Before you switch, the new or existing prescriber needs:

your current Wegovy dose and how long you have been on it
the date of your last Wegovy injection
your starting weight and your current weight
any side effects you had and how long they lasted
other medicines you take, especially insulin or a sulphonylurea such as gliclazide for diabetes

The first 12 weeks on Mounjaro

Treat the switch as a fresh start on a new medicine. Weeks 1 to 4 on 2.5mg are about tolerance, not weight loss. Weight loss usually picks up from 5mg onwards. Give each dose at least 4 weeks before deciding whether it works for you. The starter guide to the first 12 weeks covers this stage week by week, and the guide to switching from Mounjaro to Wegovy covers the move in the other direction.

Questions people ask

What dose of Mounjaro should I start on after Wegovy?

The Mounjaro licence starts everyone at 2.5mg for 4 weeks, and most prescribers stick to this. Some start at 5mg for people who were on 1.7mg or 2.4mg of Wegovy and tolerated it well, a judgement made outside the standard schedule. Your prescriber decides based on your dose, side effects and any gap.

How long should I wait between my last Wegovy injection and first Mounjaro injection?

Most prescribers advise taking your first Mounjaro dose on the day your next Wegovy dose would have been due, 7 days after your last injection. Neither SmPC sets a formal washout. Do not take both in the same week.

Is 2.5mg Mounjaro equal to a Wegovy dose?

There is no official equivalence. The two medicines work differently, so a milligram of one does not match a milligram of the other. Tables found online are rough guides drawn up by individual services, not licensed advice.

Will I lose weight when I first switch to Mounjaro?

Possibly not at first. The 2.5mg starting dose is designed to let your gut adjust, so appetite may feel stronger than on a high Wegovy dose for a few weeks. Most people see the effect build as they move up to 5mg and beyond.

Will I get side effects again when I switch to Mounjaro?

Many people get some nausea, bloating or bowel changes in the first weeks, even if they had settled on Wegovy. Starting at 2.5mg and stepping up every 4 weeks or more keeps this to a minimum. Contact your prescriber if you cannot keep fluids down.

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

There is no official conversion table between Wegovy (semaglutide) and Mounjaro (tirzepatide). The Mounjaro licence starts everyone at 2.5mg for 4 weeks, and most prescribers follow this, though some start at 5mg for people on a high Wegovy dose. The usual timing is to take your first Mounjaro dose on the day your next Wegovy dose would have been due, and never use both in the same week.

Neither the Wegovy nor the Mounjaro SmPC gives a dose conversion between the two medicines
The Mounjaro SmPC sets a 2.5mg starting dose for 4 weeks, then 2.5mg steps with at least 4 weeks on each
The Wegovy SmPC advises against using semaglutide with any other GLP-1 medicine at the same time
The usual gap is 7 days: your first Mounjaro dose replaces your next Wegovy dose
In SURMOUNT-5, average weight loss at 72 weeks was 20.2% on tirzepatide and 13.7% on semaglutide

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