Wegovy v Mounjaro: what the comparison really comes down to

What is the actual difference between Wegovy and Mounjaro?

The short version: they are different molecules that hit the appetite system in slightly different ways. Mounjaro contains tirzepatide, which activates two receptors your body uses to manage hunger and blood sugar, GIP and GLP-1. Wegovy contains semaglutide, which activates just the GLP-1 receptor. Both slow how quickly your stomach empties and both turn down appetite, so day to day the experience of taking them can feel similar.

Tirzepatide is the only dual-agonist weight-loss medicine licensed in the UK, which is the main reason it draws so much attention. Whether that second receptor is the whole story behind the trial results, or just part of it, is still debated among researchers. What is clear is that the two medicines are close cousins rather than opposites.

Both are once-weekly subcutaneous injections you give yourself, rotating between the abdomen, thigh and upper arm. Mounjaro comes as a KwikPen holding four weekly doses; Wegovy is supplied in pre-filled pens too. Both need refrigerating with a limited room-temperature window, so always check the patient leaflet for the exact figures rather than guessing. If you want the plain-English version of how the two relate, we cover it in whether Wegovy is the same as Mounjaro. The National Health Service's patient page on tirzepatide and its companion page on semaglutide are a good neutral starting point too.

Which one causes more weight loss in the trials?

This is the question most people actually type when they search mounjaro v wegovy, so here is the honest answer with the numbers attached. In the SURMOUNT-5 trial, an open-label study running 72 weeks in 751 adults with obesity and without diabetes, tirzepatide produced greater average weight reduction than semaglutide 2.4mg. That is the strongest direct evidence we have, and it points one way.

Look at the individual trials and the picture holds. In SURMOUNT-1, tirzepatide at 15mg delivered around a fifth of body weight lost on average over 72 weeks. In STEP 1, semaglutide 2.4mg reached roughly 15% average reduction over 68 weeks. Different trials, different populations, so you cannot subtract one from the other cleanly, but the direction is consistent.

The gap has since narrowed. The MHRA approved a higher 7.2mg dose of Wegovy in 2026, and trials at that dose reported around 20.7% average weight loss over 72 weeks, close to tirzepatide 15mg territory. So the newest Wegovy is a stronger contender than the older 2.4mg figures suggest. Averages are not promises, of course; individual results vary widely and no prescriber can guarantee a number. You can read the SURMOUNT-5 findings via the tirzepatide trial paper in the New England Journal of Medicine. We go deeper on the numbers in our piece on whether Wegovy is as good as Mounjaro.

How do the two compare side by side?

Sometimes it helps to see it laid out. Here are the headline facts, drawn from the manufacturers' licensing and the trial data, with the caveat that a table can never capture how a medicine behaves in one person's body.

A few things the grid does not show. Both carry the Black Triangle symbol, meaning the MHRA wants any suspected side effect reported so its safety picture keeps building. Both start low and step up gradually under a prescriber's direction. And the maximum-dose figures matter less than tolerated dose: the best medicine is the one you can actually stay on comfortably. For a fuller cost-and-value breakdown we keep the numbers in our Mounjaro and Wegovy price comparison.

Are the side effects different between the two?

Not dramatically. Both medicines share a gastrointestinal-led side-effect profile, which makes sense given they both slow the stomach and act on GLP-1. The commonly reported effects include feeling sick, being sick, loose or hard stools, indigestion, burping, tiredness, headache and reactions where you inject. These tend to be most noticeable in the first days after starting or after a dose increase, and for many people they settle within a couple of weeks as the body adjusts.

Because Mounjaro reaches a higher maximum dose and pushes harder on appetite, some people find the early tolerability effects more pronounced, though this is very individual and not a rule. The starter dose on either medicine exists to let your system settle rather than to treat, which is why nobody jumps straight to a high dose.

There is one serious signal both share that is worth naming plainly. In January 2026 the MHRA highlighted acute pancreatitis as an uncommon but potentially serious reaction to GLP-1 medicines: severe stomach pain that may spread to your back, with or without vomiting, needs urgent medical attention. That advice applies to both Wegovy and Mounjaro. You can report any suspected reaction through the MHRA's Yellow Card scheme, which is also how the safety picture keeps improving. The NHS medicines page on semaglutide lists the fuller side-effect detail for that drug.

Who is eligible for each on the private route?

The licensed eligibility is broadly the same for both. As adults, you generally need a BMI of 30 or above, or 27 or above with at least one weight-related condition such as high blood pressure, high cholesterol, prediabetes, type 2 diabetes or obstructive sleep apnoea. Lower thresholds can apply for some ethnic backgrounds under UK guidance, so the number alone is not the whole test.

Neither medicine is suitable in pregnancy, when breastfeeding, or when you are trying to conceive, and neither is licensed for under-18s. A history of certain conditions, including pancreatitis and some thyroid tumours, means a prescriber will want to talk it through carefully before deciding anything. BMI on its own never guarantees a yes; our prescribers look at your full picture.

There is a contraception point specific to Mounjaro that catches people out. If you take the oral contraceptive pill, UK guidance advises adding a non-oral method such as condoms for the first four weeks of tirzepatide and for four weeks after each dose increase, because the pill's absorption may drop. NHS guidance notes there is no equivalent evidence of reduced pill effectiveness with semaglutide, so this is a genuine difference between the two. If that applies to you, flag it early. You can check the licensed criteria against NICE's appraisal of tirzepatide, and we walk through the practicalities in Mounjaro v Wegovy for weight loss.

Can you switch between them, and does that ever make sense?

Yes, people move between the two medicines fairly often, and it is a decision made with a clinician rather than something to attempt alone. Some switch because of tolerability, some because of supply, some because they have plateaued and want to try a different mechanism. There is no single conversion figure that maps a Wegovy dose neatly onto a Mounjaro one, or the other way round, because they are different molecules with different dose scales.

Because of that, a switch usually means restarting the new medicine at or near its starter level and titrating up again, rather than jumping to a matched dose. The idea of an exact one-to-one swap is a common misunderstanding. Your prescriber weighs where you are, how you have tolerated treatment so far, and what you are trying to achieve.

If you are thinking about it in either direction, we have dedicated guidance: moving from tirzepatide to semaglutide is covered in going from Mounjaro to Wegovy, and the reverse journey in switching from Wegovy back to Mounjaro. One thing to avoid entirely: never take both at once. We explain why in whether you can mix Mounjaro and Wegovy. Stacking two GLP-1 medicines is not how either is licensed and it raises the risk of side effects without a proven benefit.

How do you get either one safely in the UK?

Both Wegovy and Mounjaro are prescription-only medicines, so the only lawful route is a prescription following a proper clinical assessment. On the NHS, access is tightly phased: tirzepatide is being rolled out to the highest-need groups first, and Wegovy is offered through specialist weight-management services with long waiting lists. The criteria are strict and change in stages, which is why many people look at the private route instead.

With nume, the process is straightforward. You complete a free consultation, and a GPhC-registered Independent Prescriber reads your answers the same day, not an algorithm. We verify your identity with photo ID and check your weight on video. If treatment is clinically approved and you ordered before 12pm on a weekday, your pen is dispatched the same day and arrives free the next working day by DPD, tracked on your phone, in a plain unbranded box. There are no subscriptions; every repeat order is reviewed again.

Whichever medicine you are considering, check the pharmacy is real. You can confirm any UK online pharmacy on the GPhC register before you part with money. Be wary of sellers offering these injections without a clinical assessment, social-media sellers, and prices far below the market; the MHRA has seized large quantities of fake pens. To begin, start your free consultation and let our prescribers guide the choice.

Related questions we've answered

• Wegovy vs Mounjaro, the full comparison
• Semaglutide or tirzepatide, which molecule is which
• Is Mounjaro the same as Ozempic?
• Why there's no simple Wegovy to Mounjaro conversion chart
• Explore your weight-loss treatment options