Mounjaro, Wegovy or orlistat: comparing your options

You've Googled all three and still aren't sure which one applies to you

That's a reasonable place to be. The names circulate a lot online, sometimes interchangeably, often without much clarity about how they actually differ. Start with the basics: Mounjaro and Wegovy are injectable GLP-1 class medicines (once-weekly jabs) while orlistat is a daily capsule that works entirely differently. They don't compete in the same way a supermarket does; they occupy different rungs of the clinical evidence ladder and suit different people for different reasons.

Mounjaro (tirzepatide, made by Eli Lilly) is a dual GIP and GLP-1 receptor agonist, the only licensed weight-loss medicine in the UK to activate both pathways simultaneously. Wegovy (semaglutide, Novo Nordisk) targets the GLP-1 receptor alone. Orlistat, sold under brand names like Xenical or the lower-dose over-the-counter Alli, blocks roughly a third of dietary fat from being absorbed in the gut. None of this tells you which is right for you; it tells you they are meaningfully different medicines. The NHS patient information page on tirzepatide and the equivalent page for semaglutide explain how each works at a practical level.

One thing all three share: a prescriber has to assess whether you're medically suitable. That assessment isn't a formality.

What the trial data actually says, side by side

The numbers below are drawn from the pivotal published trials. They're averages across populations, not promises for any individual.

The SURMOUNT-5 head-to-head trial, published in the New England Journal of Medicine in 2025, compared tirzepatide directly against semaglutide 2.4mg over 72 weeks in adults with obesity and no diabetes. Tirzepatide produced greater average weight reduction. The 7.2mg Wegovy dose, approved by the MHRA in April 2026, narrows that gap considerably. Which trial result is most relevant to you depends on what dose you're eligible for, your tolerance, and what your prescriber considers appropriate.

Orlistat's numbers look smaller, and they are. It works through a completely different route (blocking a digestive enzyme, not acting on appetite hormones) so the comparison isn't quite apples to apples. For some people it's the right starting point; for others it's insufficient.

Who each medicine is licensed for, and where NICE draws the lines

All three require at minimum a BMI of 27 (with at least one weight-related condition) or 30 without one, though the specifics differ by medicine and prescriber. Lower thresholds apply for some ethnic backgrounds under UK guidance, your prescriber will apply these to your assessment.

NICE recommends tirzepatide (TA1026, December 2024) for adults with a BMI of 35 or above plus at least one weight-related comorbidity on the NHS. NICE recommends semaglutide (TA875) within specialist weight management services for up to two years. Both recommendations come with phased NHS access criteria that are tighter than private eligibility. There's no NICE technology appraisal for orlistat, and it sits in a different regulatory category, available at lower doses without a prescription at a pharmacy counter.

For a fuller picture of how the injectable options compare head to head, if you want to understand how Wegovy and Mounjaro stack up across mechanism, trial data, and eligibility, that page goes deeper on both. If you'd prefer to approach the same question from the other direction, looking at Mounjaro versus Wegovy covers the comparison with tirzepatide as the starting point. And if you're already on one and wondering about switching, moving from Mounjaro to Wegovy covers what that involves clinically, including dose alignment and what to expect during the transition.

The right choice is rarely obvious from a table alone. Our clinical team, led by GPhC-registered prescribers, makes that determination with you, not for you. Speak to our prescribers through a free consultation to find out which treatment is clinically appropriate for your situation.

Practical differences that matter week to week

Evidence and eligibility aside, there are real-world differences between these medicines that affect daily life. Injectable treatments (Mounjaro and Wegovy) require refrigeration between 2–8°C and a subcutaneous injection once a week. If you're squeamish about needles, that's worth factoring in early rather than after your first pen arrives. Both use fine, short needles and the technique is straightforward once shown, but it's a real consideration.

Orlistat capsules are taken up to three times daily with meals containing fat. The main practical caveat is dietary: eat a high-fat meal and the unabsorbed fat has to go somewhere, oily stools and urgency are common, particularly early on. This is a predictable effect, not an allergy, and it moderates with a lower-fat diet. Some people find that mechanism helpful as a behavioural prompt; others find it disruptive enough to stop.

Timing can also play a role in which medicine fits your life. If you're planning a holiday, travelling with refrigerated pens needs thought. Monday orders placed before 12pm ship the same day, which is useful if you're managing around work schedules or a busy week. The general FAQ page covers storage and travel questions in more detail, and our team is available seven days a week if something comes up mid-treatment, reach the team via the contact page.

For the oral option: as of summer 2026, the MHRA has also approved Wegovy tablets (oral semaglutide), which require no refrigeration and are taken once daily first thing in the morning. That adds a fourth option for some people, discuss with your prescriber whether it's relevant to you. Find an overview of all options on the weight-loss treatments overview.