Introduction
If you've been researching weight loss medications, you've probably narrowed it down to two: Wegovy and Mounjaro. They're the most prescribed, the most discussed, and for most people, the most effective options available.
So which one is right for you? The honest answer is that it depends on what you're trying to achieve. Here's a quick comparison to get you started:
Mounjaro (Tirzapatide) | Wegovy (Semaglutide) | |
|---|---|---|
Mechanism | GLP-1 and GIP agonist | GLP-1 agonist |
Efficacy (weight loss over 18 months) | ~22.5kg / ~50lbs | ~15kg / ~33lbs |
Side Effects | Usually nausea, changes in bowel habits | Usually nausea, changes in bowel habits |
Dosing Scheudle | Start dose 2.5mg, potential increase every 4 weeks | Start dose 0.25mg, potential increase every 4 weeks |
Price | Starts at £99/month | Starts at £59/month |
What they have in common
Before getting into the differences, it's worth knowing what doesn't differ between them. Both are once-weekly injections you give yourself at home. Both are gradually titrated up over several months. Both require medical supervision and ongoing review. Both work best alongside lifestyle change, not as a replacement for it. And both are available through Emerald.
The decision isn't between a "good" drug and a "bad" one. It's between two effective options optimised for slightly different goals.
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How Mounjaro works
Mounjaro is the newer of the two. Its active ingredient is tirzepatide, and what makes it distinctive is that it acts on two appetite-regulating hormone pathways at once (GLP-1 and GIP). Most weight loss medications work on one. By activating both, Mounjaro produces a stronger signal of fullness, slows how quickly your stomach empties, and helps regulate blood sugar more comprehensively.
In practical terms, you eat less, feel satisfied sooner, and lose weight faster.
How Wegovy works
Wegovy contains semaglutide, which acts on one of those same hormone pathways (GLP-1). Just like Mounjaro, It also mimics a hormone your body naturally produces after eating, telling your brain you're full and slowing digestion so that feeling lasts longer.
Wegovy is the more established option. It's been studied for longer, prescribed more widely, and has a deeper real-world track record.
Efficacy
For most people, the first question is simply: how much weight can I lose?
In the first head-to-head trial comparing the two drugs, people on Mounjaro lost around 50 pounds (~22.5kg) on average, compared to 33 pounds (~15kg) on Wegovy, over roughly 18 months.
Both are significant results. Wegovy's outcome is well beyond what most people achieve through diet and exercise alone. But if maximum weight loss is your priority, Mounjaro currently has the edge.
That said, averages hide a lot of individual variation. Some people respond exceptionally well to Wegovy and modestly to Mounjaro, or vice versa. Your prescriber's judgment on what suits you matters more than any trial average.
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Side effects
Both drugs have similar side effect profiles. The most common are digestive (nausea, an unsettled stomach, and changes in bowel habits), and for most people, they're mild, concentrated in the first few weeks, and fade as the body adjusts.
If you know your stomach is particularly sensitive to one of those, mention it on your consultation. It's a small thing, but it can shape which drug feels more manageable day to day.
How carefully your dose is increased makes a far bigger difference to tolerability than the choice between drugs. That's why both are designed to be used under medical supervision, with the dose tailored to your response.
Beyond weight
Weight loss is the visible outcome, but the changes underneath are arguably the more important story, and this is where the two drugs diverge most meaningfully.
Wegovy has the strongest evidence for heart health. In a large trial comprised of participants with obesity and existing heart disease, Wegovy reduced the risk of serious cardiovascular events (heart attack, stroke, and cardiovascular death) by 20%. The benefit didn't depend on how much weight people actually lost, suggesting semaglutide does something protective for the cardiovascular system beyond fat reduction itself.
Mounjaro tends to improve more health markers across the board. In the head-to-head trial, people on Mounjaro saw greater reductions in waist size and blood pressure than those on Wegovy, alongside bigger improvements in blood sugar, insulin, and cholesterol. Mounjaro has also been shown to help with sleep apnoea and certain heart conditions linked to obesity.
On body composition, both drugs cause some loss of lean muscle alongside fat, which is why resistance training and adequate protein intake matter on either.
Which one is right for you?
These above are all starting points, not answers. The right medication depends on your medical history, your current health markers, your goals, and how your body actually responds once you begin treatment. None of that can be predicted from an article.
What this article can do is get you to your consultation knowing which questions to ask.
Book your consultation
Complete your eligibility check, and if eligible, you'll be matched with a doctor who'll review your health profile and recommend the right medication and dose for you. Both Wegovy and Mounjaro are available through Emerald.
References
"Acute Pancreatitis." NHS, www.nhs.uk/conditions/acute-pancreatitis/. Accessed 3 June 2026.
Aronne, Louis J., et al. "Tirzepatide as Compared with Semaglutide for the Treatment of Obesity." The New England Journal of Medicine, vol. 393, no. 1, 3 July 2025, pp. 26–36. NEJM, doi:10.1056/NEJMoa2416394.
Lincoff, A. Michael, et al. "Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes." The New England Journal of Medicine, vol. 389, no. 24, 14 Dec. 2023, pp. 2221–32. NEJM, doi:10.1056/NEJMoa2307563.
Malhotra, Atul, et al. "Tirzepatide for the Treatment of Obstructive Sleep Apnea and Obesity." The New England Journal of Medicine, vol. 391, no. 13, 2024, pp. 1193–1205. NEJM, doi:10.1056/NEJMoa2404881.
"Mounjaro KwikPen 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, 15 mg Solution for Injection in Pre-Filled Pen — Summary of Product Characteristics." Electronic Medicines Compendium, Eli Lilly and Company Limited, www.medicines.org.uk/emc/product/13941/smpc. Accessed 3 June 2026.
Packer, Milton, et al. "Tirzepatide for Heart Failure with Preserved Ejection Fraction and Obesity." The New England Journal of Medicine, vol. 392, no. 5, 30 Jan. 2025, pp. 427–37. NEJM, doi:10.1056/NEJMoa2410027.
"SURMOUNT-5: Greater Loss of Weight, Waist Circumference With Tirzepatide Than Semaglutide." American College of Cardiology, 10 July 2025, www.acc.org/Latest-in-Cardiology/Journal-Scans/2025/07/10/09/09/SURMOUNT-5. Accessed 3 June 2026.
"Wegovy 0.25 mg, 0.5 mg, 1 mg, 1.7 mg, 2.4 mg Solution for Injection in Pre-Filled Pen — Summary of Product Characteristics." Electronic Medicines Compendium, Novo Nordisk Limited, www.medicines.org.uk/emc/product/13895/smpc. Accessed 3 June 2026.
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