Switching from Wegovy to Mounjaro

Switching from Wegovy (semaglutide) to Mounjaro (tirzepatide) is possible and fairly common in the UK, but it should be planned with a prescriber rather than done on your own. People usually switch because they have not lost as much weight as hoped, because side effects have been hard to manage, or because of changes in supply or cost. There is no official dose conversion between the two. The Mounjaro SmPC starting dose is 2.5mg weekly, and many prescribers start there, with the first Mounjaro injection typically given when the next Wegovy dose would have been due. This guide explains the evidence, the practical steps and the questions to ask.

Wegovy and Mounjaro: how they differ

Both medicines are once-weekly injections licensed in the UK for weight management in adults with a BMI of 30 or more, or 27 to under 30 with at least one weight-related condition. Both are used alongside a reduced-calorie diet and increased physical activity. But they work in slightly different ways.

Our guides to how Mounjaro works and how Wegovy works explain the biology, and our Mounjaro vs Wegovy comparison covers the differences in depth.

Why people switch from Wegovy to Mounjaro

Not losing enough weight

Response to GLP-1 medicines varies widely. In STEP 1, semaglutide 2.4mg produced an average weight loss of about 15% over 68 weeks, but some people lost much more and some much less. NICE TA875 advises that semaglutide should be stopped in the NHS if less than 5% of initial weight has been lost after six months. People who have reached their maximum tolerated Wegovy dose without enough benefit sometimes ask about Mounjaro. See our guide to GLP-1 non-responders.

A weight loss plateau

Weight loss on any GLP-1 medicine usually slows and levels off over time. A plateau is expected and does not necessarily mean the medicine has stopped working. Before switching, it is worth reviewing diet, protein intake, activity, sleep and other medicines. Our guide to weight loss plateaus on GLP-1 medicines explains this.

Side effects

Some people find Wegovy's side effects, such as nausea, vomiting or reflux, difficult to manage. Mounjaro has a similar side-effect profile, so switching will not necessarily mean fewer side effects, but individual tolerance varies.

Supply, access or cost

Changes in availability, NHS eligibility or private costs can prompt a switch. Costs for both medicines vary by dose and provider, and Lilly increased the UK list price of Mounjaro from September 2025. We don't quote prices in our guides; see our prices page for what affects cost.

What the evidence says

SURMOUNT-5: the head-to-head trial

SURMOUNT-5, published in the New England Journal of Medicine in 2025, directly compared tirzepatide with semaglutide in 751 adults with obesity who did not have type 2 diabetes. Participants received the maximum tolerated dose of tirzepatide (10mg or 15mg) or semaglutide (1.7mg or 2.4mg) for 72 weeks.

Our guide to SURMOUNT-5: tirzepatide vs semaglutide covers the trial in detail.

What SURMOUNT-5 doesn't tell us

SURMOUNT-5 compared people starting each medicine. It did not study people switching from semaglutide to tirzepatide. Someone who has not responded well to semaglutide may or may not respond better to tirzepatide, and the trial's average results cannot predict an individual's outcome. Evidence specifically on switching is more limited, coming largely from smaller studies and clinical experience rather than large randomised trials.

Cardiovascular evidence

Wegovy has evidence from the SELECT trial, which showed a 20% reduction in major cardiovascular events (heart attack, stroke or cardiovascular death) in people with established cardiovascular disease and overweight or obesity. This led to a UK licence that covers reducing cardiovascular risk in some adults. At the time of writing, comparable cardiovascular outcome evidence for tirzepatide in people without diabetes is still emerging. If you have heart disease, this is an important point to discuss before switching.

How the switch usually works

Every switch should be individualised by a prescriber. The steps below describe common practice, not a set protocol.

Step 1: Review with your prescriber

Your prescriber will want to know:

• Your current Wegovy dose and how long you have been on it
• Your starting weight, current weight and the trend
• Side effects you have experienced
• The date of your last Wegovy injection
• Any changes in your health, medicines or pregnancy plans
• Your reasons for wanting to switch

If you are also changing provider, expect identity and weight checks and a request for evidence of your Wegovy prescription. See our guide to switching providers mid-treatment.

Step 2: Choose the timing

The most common approach is to take the first Mounjaro injection on the day your next Wegovy dose would have been due, roughly seven days after your last Wegovy injection. This avoids overlap and avoids a long gap.

Semaglutide has a long half-life, so some semaglutide is still in your body for several weeks after your last dose. Starting Mounjaro at a low dose takes this into account.

Never take Wegovy and Mounjaro at the same time, and do not use up your remaining Wegovy pens alongside Mounjaro.

Step 3: Choose the starting dose

There is no official conversion between Wegovy and Mounjaro doses, and the two medicines cannot be directly compared milligram for milligram. The Mounjaro SmPC states a starting dose of 2.5mg once weekly, increasing by 2.5mg steps at least every four weeks.

Many prescribers start at 2.5mg even after Wegovy, because it is the licensed starting dose and minimises side effects. Some may take a different approach for people who have tolerated higher semaglutide doses well and recently, but this is a clinical judgement outside the SmPC's standard schedule and must be decided by your prescriber. Our Mounjaro dosing schedule guide explains the steps.

Starting at 2.5mg can feel like going backwards, and some people notice appetite returning in the first weeks. This is common, and it usually improves as the dose increases.

Step 4: Learn the new pen

The Mounjaro KwikPen works differently from the Wegovy FlexTouch pen. Read the instructions for use carefully, and ask your pharmacist for guidance. Our guide to injecting with the Mounjaro KwikPen walks through each step. Make sure you know how many doses each pen contains and how to dispose of it safely.

Step 5: Review contraception

If you could become pregnant and use oral contraception, the Mounjaro SmPC advises switching to a non-oral method, or adding a barrier method such as condoms, for four weeks after starting Mounjaro and for four weeks after each dose increase. This advice does not apply in the same way to Wegovy, so it is a genuine change. See our guide to GLP-1 medicines and contraception.

Step 6: Monitor and review

Your prescriber should review you before each dose increase, checking weight, side effects and wellbeing. NICE TA1026 advises that, in the NHS, tirzepatide should be stopped if less than 5% of initial weight has been lost after six months on the highest tolerated dose. Private services may apply similar principles.

Common switching scenarios

Every situation is different, but prescribers often encounter a few typical scenarios. The notes below describe the kinds of factors a prescriber may weigh. They are not instructions, and your prescriber will decide what is right for you.

Limited weight loss on a full Wegovy dose

Someone who has been on Wegovy 2.4mg for several months, tolerates it well, but has lost less weight than expected may ask about Mounjaro. A prescriber is likely to review adherence, timing of injections, diet, activity, sleep and other medicines first. If a switch is agreed, they will choose a starting dose and plan regular reviews, with clear criteria for judging whether Mounjaro is working.

Side effects on Wegovy

Someone who has struggled with nausea or reflux on Wegovy may wonder whether Mounjaro would be easier. Because the side-effect profiles are similar, a prescriber may first consider whether staying on a lower Wegovy dose, or slowing dose increases, could help. If a switch goes ahead, starting Mounjaro at 2.5mg and increasing slowly is a common approach.

A gap in treatment

If you have had a break from Wegovy, for example because of supply problems, illness or cost, the longer the gap, the more likely a prescriber is to treat a switch like starting afresh, at the lowest dose. Side effects can be more noticeable after a break.

Changing provider at the same time

If you are switching medicine and provider together, expect a full reassessment, including identity and weight verification, and a request for evidence of your Wegovy prescription and recent doses.

What to expect in the first 12 weeks after switching

Not everyone increases dose at every opportunity. Staying on a dose that works and is well tolerated is a legitimate choice. Our guide to the Mounjaro results timeline describes typical patterns in more detail.

Practical points

• Leftover Wegovy pens. Don't use them alongside Mounjaro. Ask your pharmacy how to dispose of unused medicine safely; pharmacies can usually take back unwanted medicines. Don't give them to anyone else.
• Injection day. You can usually keep the same weekly injection day. The Mounjaro SmPC allows the day to be changed if needed, as long as there are at least three days between doses.
• Missed doses. The rules differ: a missed Mounjaro dose can be taken within four days, compared with five days for Wegovy. After that, skip the dose and continue on your usual day.
• Storage. Keep unused Mounjaro pens in the fridge and check the leaflet for how long they can be kept at room temperature.
• Nutrition and muscle. Keep focusing on protein, fluids and strength exercise during the transition, especially if appetite changes. See our guide to preserving muscle on GLP-1 treatment.
• Record keeping. Note the date of your last Wegovy dose, your first Mounjaro dose and each increase, along with your weight and any side effects. This helps your prescriber at each review.

Side effects when switching

The side effects of Mounjaro are broadly similar to those of Wegovy: nausea, diarrhoea, constipation, vomiting, indigestion and reduced appetite are the most common, especially when starting or increasing the dose.

When switching, some people:

• Notice few changes, particularly if they start at a low dose
• Experience a temporary return of gastrointestinal side effects
• Notice changes in appetite, either increased in the first weeks at a low dose, or reduced as the dose climbs

Practical tips include eating smaller meals, eating slowly, stopping when full, avoiding very fatty or spicy foods, and staying well hydrated. Our guides to nausea on GLP-1 medicines and foods that worsen GLP-1 side effects have more detail.

Serious side effects such as pancreatitis and gallbladder problems are uncommon but possible with both medicines. Red-flag symptoms are listed at the end of this guide.

Switching within the NHS

If you are receiving Wegovy through an NHS specialist weight management service, any switch would depend on local NHS pathways, NICE criteria and your clinical team's judgement. NICE TA1026 recommends tirzepatide for adults meeting specific BMI and comorbidity criteria, and NHS England is rolling it out in phases through primary care, beginning with people with the highest clinical need. Eligibility for one medicine does not automatically mean eligibility for the other. Our guides to Mounjaro on the NHS and private vs NHS weight loss treatment explain the details.

When switching may not be right

Switching is not always the right option. Your prescriber may suggest staying on Wegovy if:

• You are still losing weight steadily, or have reached a healthy plateau
• You have heart disease and the SELECT cardiovascular evidence is particularly relevant
• You have recently had significant side effects, and a pause or dose adjustment might help
• There are other factors, such as diet, sleep, activity or other medicines, that could be addressed first
• A higher Wegovy dose (up to 7.2mg, approved by the MHRA in January 2026 for adults with a BMI of 30 or more) might be an option to discuss

Our guide to switching from Mounjaro to Wegovy covers the reverse switch.

Questions to ask your prescriber

• What are the reasons you think switching might help me?
• What starting dose do you recommend, and why?
• When should I take my first Mounjaro dose?
• What should I do with my remaining Wegovy pens?
• How will my side effects be monitored?
• Do I need to change my contraception?
• How will we judge whether Mounjaro is working, and when?
• What happens if Mounjaro doesn't suit me?

Comparing services

If you are considering a switch through a private provider, it is worth comparing how different services handle switching: whether they review you thoroughly, verify your history, and offer support during the transition. Our providers page explains how we compare regulated services, and our compare tool lets you look at two side by side. For more on Mounjaro itself, see our Mounjaro hub.

When to speak to a professional

Always speak to your prescriber before switching from Wegovy to Mounjaro, and do not change medicines, doses or timing on your own. Speak to your GP or prescriber first if you have diabetes (especially if you use insulin or a sulfonylurea), heart disease, kidney disease, a history of pancreatitis or gallbladder problems, or if you are planning a pregnancy.

After switching:

• Call 999 or go to A&E if you have severe, persistent abdominal pain (with or without vomiting, sometimes spreading to your back), signs of a serious allergic reaction such as swelling of the face, lips, tongue or throat or difficulty breathing, or you collapse.
• Contact NHS 111 or your GP urgently if you have persistent vomiting or diarrhoea with signs of dehydration (dark urine, dizziness, passing very little urine), pain under the right ribs with fever or yellowing of the skin or eyes, or symptoms of low blood sugar if you have diabetes.
• Contact your prescriber if side effects are making it hard to eat or drink, if you become pregnant, if you are due to have surgery or sedation, or if your mood changes. If you have thoughts of self-harm, call 999 or Samaritans on 116 123.

Suspected side effects can be reported to the MHRA through the Yellow Card scheme.