Switching From Mounjaro to Wegovy: How Long to Wait (October 2026)

01 · The core answer

How long to wait when switching from Mounjaro to Wegovy

The honest answer is that it depends, and your prescriber decides. There is no licensed direct conversion between semaglutide and tirzepatide. Switching is done under prescriber supervision: typically the previous medicine is stopped, a washout interval is observed, and the new medicine is started at a dose your prescriber judges appropriate.¹⁸

You will see confident figures online quoting a set number of days and saying to start Wegovy on the day your next Mounjaro injection would have fallen. It is not in the licence for either product, and the right gap can differ with your dose, your side-effect history and why you are switching.

Tirzepatide has a half-life of about five days, so after a final dose it takes roughly four to five weeks to clear the system. There is no way to speed this up, and nothing needs doing while it clears.¹ Your prescriber weighs that against the risk of a gap in treatment when choosing the interval.

02 · What to do next

Is switching right for you, and what do you do next?

Start with your reason for switching, because it shapes the plan. People consider it for side effects, cost, a plateau, or a change in health circumstances. Each reason points to different questions for your prescriber, and some are better solved without switching at all, for example by holding or stepping down a Mounjaro dose within the licence.

Do not stop Mounjaro on your own and start Wegovy from another source on a guess. Book a review with whoever prescribes your current treatment, tell them the date of your last injection and your current strength, and ask for a written plan covering the gap, the Wegovy starting dose and when to review. If you are comparing the two before deciding, our weight loss clinic page explains the licensed options, and the Wegovy pen page shows current availability and first-order pricing, with the first pen from £99.99.

If you decide to stay on tirzepatide, the Mounjaro pen starts at £169.99 per month for 2.5mg at the standard price, with every dose in stock.

03 · Why no fixed gap

Why there is no fixed waiting time

The gap is not fixed because the two medicines are different and no licence defines a handover. Mounjaro contains tirzepatide, which activates two natural gut-hormone receptors at once: GIP and GLP-1. Wegovy contains semaglutide, a single-action GLP-1 medicine.¹ Each has its own dosing ladder, and neither product information gives a conversion table to the other.

That is why a prescriber, not a calculator, sets the plan. They will look at your current Mounjaro strength, how long you have been on it, how well you tolerated each step, and your reason for changing. They may also consider whether you have been unwell, vomiting or struggling to eat, because those factors affect when it is sensible to restart.

Neither a short standard gap nor waiting until the medicine has cleared is a licensed instruction. The safest course is the one your prescriber puts in writing for your own situation.

04 · Clearance and overlap

What clearance means in practice

After your final Mounjaro dose, the medicine does not vanish at once. Tirzepatide has a half-life of about five days, so it takes roughly four to five weeks to clear the system.¹

This matters because you should never run two GLP-1 medicines together, and starting Wegovy while tirzepatide is still clearing is why your prescriber chooses the interval and the restart dose.

You do not need to do anything special while it clears. Tell your prescriber about any new or lasting symptom. You can report suspected side effects through the Yellow Card scheme.¹⁹

If you still have a Mounjaro pen in use, once in use it can be kept out of the fridge at a temperature not above 30°C for up to 30 days after first use, and must then be thrown away. Do not use a pen that has been above 30°C or frozen.¹³ A part-used pen is not a reason to keep injecting while you start Wegovy.

05 · Wegovy starting dose

Which Wegovy dose do you start on?

Your prescriber chooses the Wegovy starting dose, and you should not assume it matches your Mounjaro strength. Wegovy pens come in 0.25mg, 0.5mg, 1mg, 1.7mg and 2.4mg once weekly.

The two ladders are not equivalent. Mounjaro runs from 2.5mg to 15mg in steps of 2.5mg at a minimum of 4-week intervals.¹ A person on a high Mounjaro strength therefore cannot read across to a matching Wegovy strength. Expect your prescriber to choose a cautious restart and step up as you tolerate it.

This also affects expectations. After a switch, the early weeks are an adjustment period again. Progress is best judged by trend over months rather than individual weigh-ins.

Ask your prescriber directly: what is my first Wegovy dose, how long do I stay on it, and what should I do if I miss one? Write the answers down alongside your injection day.

06 · Side effects after switching

What to expect in the first weeks after switching

Plan for a restart, not a seamless continuation. Mild nausea, altered appetite and tiredness in the first days after each injection are the commonest early effects on Mounjaro and usually settle; your Wegovy leaflet lists its own effects, which you should read before the first dose.¹⁸

Tell your prescriber about any new or lasting symptom, and you can report suspected side effects through the Yellow Card scheme.¹⁹

For a broader view of how this feels in practice, our guide to side effects when changing between these medicines covers the reverse direction in detail, and many of the principles apply both ways.

07 · Mounjaro vs Wegovy evidence

How do Wegovy and Mounjaro compare?

In the first large head-to-head trial (SURMOUNT-5), adults on tirzepatide lost on average 20.2% of body weight over 72 weeks versus 13.7% on semaglutide 2.4mg (Wegovy).¹⁵ Both are effective, licensed treatments; which suits you depends on your health profile, tolerance and prescriber advice, not the headline number alone.¹⁵

Trial averages do not predict your own result, and individual results vary. In the STEP 1 trial, adults on semaglutide 2.4mg (Wegovy) lost on average 14.9% of body weight over 68 weeks, compared with 2.4% on placebo.⁹ That is a separate trial, so it should not be set beside the SURMOUNT-5 figures as though it were head to head.

If you are switching because Mounjaro is working poorly or you are not tolerating it, the evidence is a prompt for discussion, not a verdict. If you are switching because of cost or availability, talk to your prescriber about your options.

Weight loss on these medicines is gradual. Think in months, not days.

08 · What not to do

What not to do when switching

Several shortcuts circulate online, and each carries risk. Never run two GLP-1 medicines together. That means no overlapping injections to bridge the gap.

Do not add unlicensed products. Mounjaro must not be combined with other GLP-1 medicines, unlicensed research peptides or compounded copies. These combinations have no safety data and no regulated supply chain. If something promises faster results outside a licensed pathway, that is the warning sign. Our guide to moving from Mounjaro to retatrutide explains why a medicine with no UK licence is not a switching option.

Finally, do not buy Wegovy from a seller offering to supply without a consultation or prescription. Both medicines are prescription-only, and a regulated route means a review by a GPhC-registered prescriber who can set your plan.

09 · Related switches

Other switches and how the same principles apply

The principles here recur across GLP-1 changes: stop the old medicine under supervision, allow for clearance, restart on a dose your prescriber chooses, and never overlap. If you are going the other way, our page on moving from Wegovy to Mounjaro covers it. People coming from the diabetes medicine Ozempic should read our Ozempic to Mounjaro guide. Ozempic is semaglutide licensed for type 2 diabetes only. There is no licensed direct conversion between semaglutide and tirzepatide in either direction.

If you are coming from insulin, the picture is different, and doses of insulin or sulfonylureas may need adjusting because of the risk of low blood sugar; see switching from insulin to a GLP-1 and speak to your diabetes team first.

10 · Serious side effects

Serious side effects: when to get help straight away

Serious side effects are uncommon but need urgent attention. Seek immediate medical help for: severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion) — your prescriber may need to adjust those medicines.¹

11 · Tablets and NHS access

Wegovy tablets, Foundayo and NHS access

Two GLP-1 weight-loss tablets are now licensed in the UK: Wegovy tablets (oral semaglutide, made by Novo Nordisk), approved by the MHRA in June 2026, and Foundayo (orforglipron, made by Eli Lilly), approved in August 2026. They are different medicines from Mounjaro, with their own dosing, eligibility checks and trial results, and both are prescription-only.²⁰²¹ There is no tablet form of Mounjaro.

On the NHS, Mounjaro is available but access is being phased in over several years. NICE recommends it for adults with a BMI of at least 35 plus at least one weight-related condition, and the NHS primary-care rollout began in June 2025 with the highest-need groups first.⁴⁶ NHS access to Wegovy runs through specialist weight-management services; ask your GP. If you are switching within the NHS, your NHS prescriber leads the plan.