0.5mg Wegovy compared to Mounjaro: what the dose gap really tells you

The biggest misconception: treating 0.5mg Wegovy as a like-for-like rival to any Mounjaro dose

People searching this comparison often assume 0.5mg Wegovy is a mid-range or maintenance dose being weighed against a similar Mounjaro strength. It isn't. In Wegovy's titration schedule, 0.5mg is the second step, reached after four weeks at 0.25mg, and still two further steps below the 1.7mg level and three below the 2.4mg maintenance dose used in STEP 1 trial data. At this point, most people's bodies are still adjusting; the therapeutic weight-loss effect builds as the dose rises over months.

Mounjaro's titration works on a similar principle of slow escalation, beginning at 2.5mg. That starting dose exists to let your system settle, the higher doses (up to 15mg) are where the published weight-loss data lives. So when you place 0.5mg Wegovy alongside any Mounjaro dose, you're comparing an early rung on one ladder against a medicine whose evidence base sits at quite different strengths, and our detailed look at 0.5mg Wegovy compared to Mounjaro explores exactly why that distinction matters. The broader Wegovy vs Mounjaro comparison covers the full picture once both medicines are at maintenance.

Mounjaro is a dual GIP and GLP-1 receptor agonist, the only weight-loss medicine in the UK to activate both pathways simultaneously. Wegovy acts on GLP-1 receptors alone. Both slow gastric emptying and reduce appetite, but the mechanisms differ, and so do the trial populations and result profiles. Neither medicine should be chosen on dose number alone.

How the trial evidence compares, and why 0.5mg doesn't feature in it

The headline clinical data that regulators and prescribers work from comes from maintenance-dose trials. The STEP 1 trial (published in the New England Journal of Medicine) ran 68 weeks at the 2.4mg Wegovy maintenance dose and recorded an average weight reduction of around 15% in adults with obesity. SURMOUNT-1, the equivalent tirzepatide trial, ran 72 weeks at 15mg and recorded average reductions of around 20–21%. SURMOUNT-5 then placed the two medicines head-to-head: tirzepatide produced greater average weight loss than semaglutide 2.4mg over 72 weeks, a result reflected in NICE's appraisal of tirzepatide (TA1026).

None of that evidence applies at 0.5mg. Someone on 0.5mg Wegovy is weeks into a process expected to last a year or more, and the comparison that matters for them is not with Mounjaro's trial averages but with where their own dose journey is heading. If you want to explore how the dose schedules map across medicines, our guide to moving from 0.5mg Wegovy to Mounjaro sets this out clearly.

A note on what's not in this picture: Ozempic and Rybelsus are also semaglutide-based medicines, but both hold UK licences for type 2 diabetes only, not weight management. They are not alternatives to Wegovy for weight loss, and a prescriber will not issue them for that purpose.

Side-effect profiles at low doses, and the storage detail worth knowing early

At 0.5mg, the most common reports from Wegovy users are gastrointestinal: nausea, loose stools, constipation and reflux. These are also common early in Mounjaro treatment. The general pattern with both medicines is that GI effects are most noticeable after starting or after a dose step, then often ease within a week or two as the body adjusts. Individual experience varies considerably.

One practical note for anyone newly starting either medicine: both Wegovy pens and Mounjaro KwikPens need refrigerating between 2–8°C. Many people keep the current pen in the fridge door, easy to reach, hard to forget. Both have a limited window for room-temperature storage once removed; check your Patient Information Leaflet for the exact timeframe rather than relying on a general figure.

For safety concerns that go beyond everyday GI discomfort (severe or persistent stomach pain that spreads to the back, signs of dehydration, or any allergic reaction) seek medical help promptly. The MHRA's Yellow Card scheme lets patients report suspected side effects directly. You can read more about our prescribers' approach to ongoing safety on the clinical team page.

What this comparison means in practice if you're choosing between them

The table below sets out the key factual differences side by side. These are characteristics of the medicines as licensed in the UK; they don't predict what will suit any individual.

Eligibility for either medicine rests on more than BMI. A prescriber looks at your full health picture, including any other conditions, medicines you take, and your own preferences. The guide to how Wegovy doses map to Mounjaro goes into more detail for people already on one medicine and considering the other, and if you are stepping up from your starting dose, our page on how 1mg Wegovy compares to Mounjaro covers what changes as the dose increases. If cost is part of your thinking, why Wegovy tends to cost less than Mounjaro explains the pricing difference honestly.

Which medicine suits you is a clinical decision our prescribers make with you, not something a side-by-side table can resolve. You can read more about how nume approaches treatment on the about us page, or head to the treatment overview to see what's available. When you're ready, speak to our prescribers through a free consultation and get a same-day clinical review.