Switching to Wegovy from Mounjaro in the UK: how the change works

Why people move from Mounjaro to Wegovy

Most people who switch give one of four reasons.

• Price. Mounjaro costs rose after the 2025 list price change. At some doses and pharmacies Wegovy now works out cheaper per month.
• Supply. A pharmacy may run short of a Mounjaro strength for a few weeks.
• Side effects. Some people find nausea, reflux or bowel changes easier on one medicine than the other. You only find out by trying.
• Results. Some people stall on Mounjaro and hope Wegovy will restart weight loss. The trial evidence does not support this on average, so talk through dose, eating and missed injections with your prescriber first. Our page on when weight loss slows covers the usual causes.

Wegovy also has a UK licence to lower the risk of heart attack and stroke in adults with heart disease, based on the SELECT trial. If that applies to you, raise it with your prescriber.

Should you switch? A quick checklist

Answer these before you book a consultation. If you tick most of the first four, a switch is worth discussing.

What the head-to-head trial found

SURMOUNT-5 is the only trial to compare the two medicines directly. It gave 751 adults with obesity, without diabetes, the highest dose of either medicine they could tolerate for 72 weeks. Average weight loss was 20.2% with tirzepatide and 13.7% with semaglutide. Nausea, diarrhoea and constipation showed up at similar rates in both groups.

Two points matter for you. Averages hide individuals, and some people do better on semaglutide. The trial also used top doses, while many people in the UK stay on a middle Mounjaro dose. Your own comparison may look different.

How the switch works

Timing

Your new pharmacy sets the timing, so follow its instructions. Both medicines are once-weekly injections. Many pharmacies tell you to take your last Mounjaro dose as normal, then your first Wegovy dose seven days later on your usual injection day. Others ask you to wait longer, sometimes 28 days, and then start again from 0.25mg. Never take both in the same week.

Choosing the starting dose

The Wegovy and Mounjaro product information on the eMC gives no conversion between the two. Your prescriber chooses based on your current Mounjaro dose, how long you have taken it and how well you tolerate it. Many start at 0.5mg or 1mg. Some go back to 0.25mg to keep nausea down. Each step usually lasts at least 4 weeks.

Stay on a level or move up

You do not have to climb to 2.4mg. If a dose controls your appetite and the side effects are fine, you can stay on it. If you want more effect, you can step up. Agree each change with your prescriber. The 7.2mg dose is an option only after time on 2.4mg and only if your prescriber thinks it suits you.

If you have missed doses

Be careful here. If you have not injected Mounjaro for 2 weeks or more, your body has lost some tolerance. Starting Wegovy at a higher step after a gap can bring back strong nausea and vomiting. Prescribers often start lower after a break. The Wegovy SmPC also advises that if you miss more than 2 weeks of Wegovy itself, you may need to restart the dose steps.

What to tell the pharmacy

• Your current Mounjaro dose and how long you have been on it.
• The date of your last injection and any missed doses in the past 2 months.
• Your starting weight, current weight and any side effects you still get.
• Other medicines you take, including the contraceptive pill. Mounjaro can reduce how well oral contraceptives work during dose increases.
• Any history of pancreatitis, gallbladder problems or eye disease linked to diabetes.

Have proof of your current treatment ready. Most pharmacies ask for a clear photo of the prescription label stuck to your Mounjaro box, showing your name, the dose and the pharmacy. Some also ask for a screenshot of your last order.

If you are moving pharmacy at the same time, our switching pharmacy guide lists the steps. Do not keep any Mounjaro pens to use alongside Wegovy.

What to expect in the first weeks

Nausea and bowel changes that had settled on Mounjaro may come back for a while. The NHS lists feeling sick, diarrhoea, constipation and stomach pain as the most common side effects of Wegovy. Small, low-fat meals help. So does stopping eating when you feel full.

Your appetite may feel less controlled until you reach a dose that suits you. A little weight regain in the first month is common. Judge the switch over 3 months rather than 3 weeks. Our nutrition guide applies to both medicines.

The pens differ too. Read the leaflet in your Wegovy pack before the first injection, even if you are used to the Mounjaro KwikPen. See a doctor urgently for severe stomach pain that spreads to your back, as this can be a sign of pancreatitis.

Check the cost before you switch

What you pay depends on the pharmacy, not the list price. Prices and discount codes change every few weeks, and your current pharmacy will rarely tell you when a rival is cheaper. Before each reorder, see what other pharmacies are offering. Compare the full monthly price at your likely starting dose and the dose you expect to stay on, with delivery, rather than the first-month deal alone.

• For Wegovy injection prices by dose, see iGovy.
• For Wegovy pill prices, see Ogovy. For Foundayo prices and discount codes, see Dayo.
• To stay on Mounjaro for less, check the discount Mounjaro price list and the full Mounjaro price comparison.

Moving pharmacy on Mounjaro sometimes saves as much as switching medicine.

Daily pill options: Wegovy pill and Foundayo

If you want to stop injecting, two daily pills are available privately in the UK. Neither is on the NHS for weight loss at present.

• Wegovy pill (oral semaglutide). Taken each morning on an empty stomach with a small sip of water, then a wait before food. Compare Wegovy pill prices on Ogovy.
• Foundayo (orforglipron). Approved by the MHRA on 10 August 2026. You can take it at any time of day with no food or water rules. Compare Foundayo prices on Dayo.

Weight loss on the pills is lower than on Mounjaro. In trials, the Wegovy pill 25mg gave about 13.6% average weight loss over 64 weeks. Foundayo gave about 11.2% at the top 36mg dose over 72 weeks. Mounjaro gave 20.2% in SURMOUNT-5. If you mainly want the biggest result, an injection is the stronger choice. If needles are the problem, a pill may still suit you. Ask your prescriber how to time the move.

Switching back

If Wegovy does not suit you, a move back to Mounjaro works the same way. After a break of more than a few weeks, prescribers usually restart at 2.5mg or 5mg rather than your old dose. Our restarting guide explains more, and the Wegovy to Mounjaro switching guide covers the move in that direction.