If you're weighing up Mounjaro vs Wegovy and which is better, the honest answer is: it depends on what you're optimising for. Both are licensed, once-weekly injections used for weight management in the UK — but they work slightly differently, deliver different average results and cost very different amounts. This guide puts the two side by side on the measures that actually separate them, using price data from our tracker of UK providers, last checked 17 July 2026.
Neither is universally "better". Mounjaro tends to produce more weight loss on average; Wegovy has the longer track record and a proven heart benefit. Below we break down exactly where each one wins so you can match the medicine to your own goals.
Key takeaway: Mounjaro (tirzepatide) delivers the largest average weight loss — around 21–22% at the higher doses over 72 weeks — and beat Wegovy head-to-head in the SURMOUNT-5 trial (~20% vs ~14%). Wegovy (semaglutide) is cheaper to start, has the longest UK track record, and is the only one shown to cut heart-attack and stroke risk in people with existing heart disease. Both are prescription-only; a prescriber decides which suits you. And the same medicine can cost far more at one provider than another — always compare.
Mounjaro vs Wegovy: the core difference
Wegovy contains semaglutide, which mimics one gut hormone (GLP-1) to reduce appetite and slow stomach emptying. Mounjaro contains tirzepatide, a "twincretin" that mimics two hormones (GIP and GLP-1). That extra mechanism is widely thought to explain why Mounjaro tends to produce larger average weight loss in trials.
Both are once-weekly injections you self-administer with a pen, both start low and step up slowly, and both work best alongside changes to diet and activity. Our deep-dive on what's actually different covers the mechanisms in more detail.
Head-to-head: the numbers that matter
| Mounjaro | Wegovy | |
|---|---|---|
| Active ingredient | Tirzepatide (dual GIP + GLP-1) | Semaglutide (GLP-1) |
| How it's taken | Weekly injection, 2.5–15 mg | Weekly injection, 0.25–2.4 mg |
| Average trial weight loss | 21.4–22.5% at 10–15 mg over 72 weeks (SURMOUNT-1) | ~15% at 2.4 mg over 68 weeks (STEP 1) |
| Head-to-head (SURMOUNT-5) | ~20% average loss | ~14% average loss |
| Standout strength | Largest average weight loss | Longest track record; proven heart benefit (SELECT) |
| Starter month from | £131.00 | £89 |
| Top maintenance dose from | £266.00 (15 mg) | £174.99 (2.4 mg) |
"From" prices are the cheapest per 4 weeks among our tracked UK providers, last checked 17 July 2026. The trials enrolled different populations over different durations, so cross-trial percentages are a guide, not a precise ranking.
Best for sheer weight loss: Mounjaro
If your single yardstick is kilograms lost, Mounjaro leads — and not narrowly. In SURMOUNT-1, participants averaged 21.4% loss at 10 mg and 22.5% at 15 mg over 72 weeks, versus 2.4% on placebo, and about 90% of people on 15 mg lost at least 10% of their body weight. In SURMOUNT-5, the direct head-to-head against Wegovy, tirzepatide came out ahead at roughly 20% versus about 14%.
Mounjaro is MHRA-licensed for weight management and recommended by NICE (TA1026, December 2024). The trade-off is cost: while its cheapest starter month (£131) is actually competitive, the higher maintenance doses climb steeply. Our efficacy comparison lays out the real numbers dose by dose.
Best for track record and heart protection: Wegovy
Wegovy has been prescribed in the UK longer than Mounjaro, so it carries more real-world experience and trial data. It also holds one card Mounjaro can't yet match: in the SELECT trial it cut heart-attack and stroke risk in people with existing cardiovascular disease — the only weight-loss injection with that proof to date.
It's also the cheapest way in, with a starter month from £88.96. If around 15% average loss meets your goal — and for many people it comfortably does — the case for paying for Mounjaro's extra few percentage points is weaker than the headlines suggest.
Our recommended provider, The Weight Clinic, stocks both medicines, offers £35 off your first order with code NEWME, refunds you if the prescriber declines, and runs monthly video reviews to keep your dose on track.
Side effects: broadly similar
Both belong to the same broad class and share the same common side effects: nausea, diarrhoea, constipation, vomiting and tiredness. These are usually worst when starting or stepping up a dose, which is why both are titrated slowly. Rarer but more serious risks include pancreatitis, gallstones and dehydration that can strain the kidneys.
If you experience a side effect, report it through the MHRA Yellow Card scheme. Our honest side-effect comparison looks at how the two compare in practice.
Price: don't overpay for the same pen
Both medicines vary enormously in price between providers. Across our tracker, the same Mounjaro pen ranges from £131 to £220 for the 2.5 mg starter dose — an £89 spread. Wegovy ranges from £88.96 to £185 at the 0.25 mg starter dose. Many providers also run first-month promotions and discount codes that only apply to the starter dose.
Because you'll usually step up over several months, look at the whole dose ladder rather than just the headline first-month price. The full comparison lives on our homepage price table, and our prices-compared guide explains how to read it.
So, which is better for you?
Choose Mounjaro if maximum average weight loss is your priority and you're comfortable with the higher maintenance cost. Choose Wegovy if you want the longest track record, a lower entry price, or you have existing heart disease where the SELECT data matters. Either way, eligibility is typically a BMI of 30+, or 27+ with a weight-related condition — and a prescriber makes the final call.
For a structured way to decide, our 5-question framework and the wider 2026 UK comparison are good next reads.
Ready to compare on a real prescription? The Weight Clinic is our recommended provider — GPhC-registered, with £35 off your first order using code NEWME, a refund if the prescriber decides the medicine isn't right for you, and monthly video reviews to support your progress.
Frequently asked questions
Is Mounjaro more effective than Wegovy?
On average, yes. In the SURMOUNT-5 head-to-head trial, tirzepatide (Mounjaro) produced about 20% average weight loss versus about 14% for semaglutide (Wegovy). Individual results vary, and a prescriber decides which is appropriate for you.
Which is cheaper, Mounjaro or Wegovy?
Wegovy is cheaper to start, from £88.96 per 4 weeks versus £131 for Mounjaro at the starter dose among our tracked UK providers. Prices rise with higher doses, and promotions usually apply only to the first month, so check the full dose ladder before committing.
Can I switch from Wegovy to Mounjaro?
Many people do switch, often for greater weight loss or to manage side effects, but it must be done under a prescriber's guidance. They'll advise on the right starting dose and timing rather than you swapping directly at an equivalent strength.
Do Mounjaro and Wegovy have different side effects?
They share the same common side effects — nausea, diarrhoea, constipation, vomiting and tiredness — and similar rare risks such as pancreatitis and gallstones. Report any side effects via the MHRA Yellow Card scheme.
Which is better if I have heart disease?
Wegovy is the only weight-loss injection shown, in the SELECT trial, to reduce heart-attack and stroke risk in people with existing cardiovascular disease. Discuss your history with a prescriber, as this may influence the choice.
Am I eligible for either medicine?
Private eligibility is typically a BMI of 30+, or 27+ with a weight-related condition. Both are prescription-only medicines, so a GPhC-registered pharmacy or CQC-regulated clinic prescriber will assess your suitability. This article is information only, not medical advice.