Is Semaglutide as Good as Mounjaro for Weight Loss?

The biggest misconception: semaglutide and tirzepatide work the same way

The most common misunderstanding is that these two medicines are interchangeable versions of the same thing. They are not. Semaglutide, which is the active ingredient in Wegovy, activates a single receptor involved in appetite regulation: the GLP-1 receptor. Tirzepatide, the active ingredient in Mounjaro, activates two receptors simultaneously, GLP-1 and GIP. That dual action is genuinely different at a physiological level, not just a marketing angle.

Both slow gastric emptying and reduce appetite, which is why the side-effect profiles overlap so much. But the additional GIP pathway appears to drive greater energy expenditure and stronger appetite suppression in many people, and that difference shows up clearly in the clinical data. If you have been told that one is simply a newer version of the other, that framing understates how the mechanisms differ. Our comparison of Mounjaro and semaglutide covers this in more depth.

Mounjaro is also the only dual-agonist weight-loss medicine currently licensed in the UK, which makes it structurally different from every GLP-1 medicine that preceded it. That distinction matters when a prescriber is weighing up which option suits a patient's physiology, health history and goals.

What the trial numbers actually show

The strongest evidence comes from SURMOUNT-5, a 72-week open-label head-to-head trial in 751 adults with obesity and no diabetes, comparing tirzepatide directly against semaglutide 2.4mg. Tirzepatide produced greater average weight reduction. Earlier pivotal trials give useful context: SURMOUNT-1 reported average body-weight reductions of around 20 to 21 percent at the 15mg dose over 72 weeks, while the STEP 1 trial for semaglutide 2.4mg, published in the New England Journal of Medicine, reported approximately 15 percent average reduction over 68 weeks.

Novo Nordisk has since received MHRA approval for a 7.2mg semaglutide dose, with trials reporting around 20.7 percent average weight loss, which narrows the gap considerably. A full breakdown of how the two drugs compare at their respective doses is on the Wegovy vs Mounjaro comparison page.

Numbers from clinical trials are averages across large study populations, not predictions for any individual. Suitability is a clinical decision. You can read a fuller account of whether Wegovy is as effective as Mounjaro on a dedicated page.

Side effects, tolerability and practical differences

Both medicines share a broadly similar side-effect profile because both slow gastric emptying. Nausea, constipation, diarrhoea, indigestion, fatigue and headache are the most common complaints, typically peaking after a dose increase and easing over the following days to a couple of weeks. If you are trying to decide between the two, it helps to understand whether Wegovy is as strong as Mounjaro in practice, because tolerability and potency are closely linked when choosing a starting point. Neither medicine is clearly better tolerated than the other across the general population; individual response varies considerably.

One practical difference that comes up in consultations is contraception. Women taking tirzepatide should add a non-oral method for the first four weeks of treatment and for four weeks after each dose increase, because oral contraceptive absorption may be reduced. The same precaution is not indicated for semaglutide based on current evidence. NHS England's guidance on weight-management injections covers this, along with advice on HRT and surgical procedures.

Storage is identical for both: refrigerated between 2 and 8 degrees Celsius. For most people that means the fridge door, though the exact out-of-fridge window for travel or if a pen is accidentally left out should always be confirmed in the Patient Information Leaflet rather than estimated.

Both carry a Black Triangle designation, meaning the MHRA requires additional monitoring. Any suspected side effect can be reported at the MHRA's Yellow Card scheme.

Which one is right? That question belongs in a consultation

A fair answer to 'is semaglutide as good as Mounjaro' is: on average, across the trial populations studied, tirzepatide produced greater weight loss. Researchers have examined this closely, and our dedicated page on whether semaglutide is as good as tirzepatide walks through the evidence in detail. For a specific person, the right choice depends on their BMI, existing health conditions, current medications, contraceptive or HRT situation, and their own preferences about the treatment schedule. Tolerability, prior experience and cost all feed into the decision too.

There is also a broader category to be aware of: Ozempic is also semaglutide, but it is licensed for type 2 diabetes in the UK, not weight management. Wegovy and Mounjaro are the two medicines licensed specifically for weight loss, and those are the ones a prescriber would consider.

If you want to explore which medicine our prescribers think suits your situation, our clinical team reviews every consultation personally, the same day, and will discuss the clinical reasoning with you. A prescriber, not an algorithm, makes that call. You can read more about the full range of options on our weight-loss treatment overview, or go straight to start your free consultation.