Looking at medical weight loss in the UK? You've probably come across three names already: Wegovy, Mounjaro and orlistat. And as of 2026, more oral weight loss medicines have been approved in the UK, so there are now more options to weigh up.
This guide compares Wegovy injections, the newer Wegovy tablets, Mounjaro, Foundayo and orlistat. We'll look at how each one works, how much weight you might lose, the side effects, and who's eligible in the UK.
There's no single best option. The right fit depends as much on your routine and health as on the trial results.
How does each weight loss treatment work?
All of these treatments support weight management, but they work in different ways. That's part of why their results and side effects differ.
Wegovy (semaglutide)
Wegovy contains semaglutide. It mimics GLP-1 (glucagon-like peptide-1), a hormone your gut releases after you eat.
By activating GLP-1 receptors, it helps you feel fuller for longer and slows how quickly food leaves your stomach. It also reduces how often and how strongly you get food cravings.
It's a once-weekly injection using a pre-filled pen. The dose is increased gradually up to a maintenance dose of 2.4mg, or 7.2mg if you need extra support after reaching the standard dose.
Wegovy tablets (oral semaglutide)
Wegovy tablets contain the same active ingredient as the injection, semaglutide, as a once-daily tablet. Semaglutide would normally be broken down by stomach acid, so the tablet comes with a few rules.
You take it on an empty stomach with a small sip of water. Then you wait 30 minutes before eating, drinking anything else or taking other oral medicines.
The dose starts at 1.5mg and goes up monthly through 4mg and 9mg to a maintenance dose of 25mg. Our Wegovy tablets dosage guide covers the full schedule in more detail.
Mounjaro (tirzepatide)
Mounjaro contains tirzepatide, which acts on two hormone receptors rather than one: GLP-1 and GIP (glucose-dependent insulinotropic polypeptide). Targeting both is thought to be part of why Mounjaro tends to produce greater average weight loss in clinical trials.
It's a once-weekly injection. The dose starts at 2.5mg and goes up every four weeks, to a maximum of 15mg.
Foundayo (orforglipron)
Foundayo (orforglipron) is made by Eli Lilly, the same company behind Mounjaro. It's a newly approved oral GLP-1 tablet, authorised by the MHRA on 10 August 2026.1 Unlike Mounjaro, it targets GLP-1 alone.
In its main trial, it produced a more modest average weight loss of around 12.4% over 72 weeks.2 But there's no injection, and no eating or drinking rules like there are with Wegovy tablets.
It isn't available to order in the UK yet, as stock is still being made and distributed. So it isn't a like-for-like alternative to Mounjaro today.
Curious how it stacks up against Wegovy's tablet? Our Foundayo vs Wegovy pill guide has the details.
Orlistat
Orlistat works completely differently. Rather than affecting your appetite or hormone signals, it blocks the enzymes that break down fat in your gut (gastric and pancreatic lipase). This stops around a third of the fat in your food being absorbed.3
That undigested fat passes through your gut and out in your stool. You take it as a capsule, usually three times a day with meals that contain fat. It's available on prescription (120mg) or over the counter at a lower dose (60mg, branded Alli).
Wegovy, Mounjaro and Foundayo all work on your appetite. Orlistat works on the fat in your food instead.
How much weight can you lose with each treatment?
Clinical trial results aren't a guarantee of what you'll lose. But they give a useful sense of scale. All the figures below come from placebo-controlled trials, where participants also followed a reduced-calorie diet and were more physically active.
- Wegovy 2.4mg - an average of 14.9% of body weight over 68 weeks in the STEP 1 trial, compared with 2.4% on placebo.4
- Wegovy 7.2mg - a higher maintenance dose for people who've plateaued on 2.4mg. The STEP UP trial found an average weight loss of around 19% over 72 weeks, compared with around 16% on 2.4mg.5
- Wegovy tablets (25mg) - an average of 13.6% over 64 weeks, including people who stopped treatment early, or 16.6% among those who took it consistently throughout the OASIS 4 trial.6
- Mounjaro - the SURMOUNT-1 trial found average weight reductions of 16.0%, 21.4% and 22.5% at the 5mg, 10mg and 15mg doses, over 72 weeks.7
- Foundayo - not available to order in the UK yet, but worth knowing for context. In the ATTAIN-1 trial, people on the highest dose lost an average of 12.4% of their body weight over 72 weeks, compared with 0.9% on placebo.2
- Orlistat - more modest. One systematic review of randomised trials found orlistat led to an average of 2.4kg more weight loss than placebo, alongside diet and exercise.8
Most of these trials ran for well over a year. Weight loss on medication builds over months, not weeks.
Apart from one trial comparing Mounjaro with Wegovy injections directly, these medicines haven't been tested head-to-head.9 So treat the figures above as a general guide, not a direct comparison.
Your own results will depend on your starting weight, your dose and how consistently you follow the diet and exercise advice that goes with treatment.
How do the side effects compare?
Side effects are one of the clearest differences between the GLP-1 medicines (Wegovy in both forms, Mounjaro and Foundayo) and orlistat.
GLP-1 medicines: Wegovy and Mounjaro
The most commonly reported side effects of both Wegovy and Mounjaro are digestive. They're classed as very common, meaning they affect more than 1 in 10 people.10,11
- Nausea - most noticeable in the early weeks of treatment or after a dose increase.
- Diarrhoea and vomiting - these usually improve as your body adjusts.
- Constipation - eating more fibre and drinking more fluids can help.
Reduced appetite is the intended effect, but it can feel quite strong for some people.
More serious but less common risks include acute pancreatitis and gallbladder problems, including gallstones, which can happen more often during rapid weight loss. Severe dehydration can also lead to acute kidney injury.
Severe upper tummy pain that spreads to your back needs urgent medical attention. It can be a sign of pancreatitis.
Both medicines slow how quickly food leaves your stomach, which can affect how some oral medicines are absorbed. With Mounjaro, this includes the contraceptive pill. If you take oral contraception, use a barrier method such as condoms as well, or switch to a non-oral method, for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase.11
Our Mounjaro side effects and Wegovy tablet side effects guides go into more detail.
Orlistat
Orlistat's side effects are almost all digestive, and they're directly linked to the unabsorbed fat passing through your gut. They include oily or fatty stools, oily spotting, needing the toilet more often, wind, and sometimes an urgent need to go.3
They're more likely after a high-fat meal. They tend to ease as you get more consistent about keeping the fat in your diet down.
Do not take orlistat with a meal that contains no fat. If you skip a meal, or it has no fat in it, you can skip that dose too.
Orlistat also reduces how well you absorb the fat-soluble vitamins A, D, E and K. A daily multivitamin, such as OneVit Complete Multivitamin, is commonly recommended to help keep your vitamin levels up. Take it at bedtime, or at least two hours after your orlistat dose.3 Our orlistat side effects guide covers the full list.
Who is eligible for each treatment in the UK?
Licensed private eligibility is broadly similar for the GLP-1 medicines. NHS access is much more restricted, and it differs between them.
- Wegovy (injection and tablets) - licensed for adults with a BMI of 30 or above, or from 27 with at least one weight-related health condition.10 On the NHS, NICE guidance (TA875) limits it to specialist weight management services, for adults with at least one weight-related condition and a BMI of 35 or above, or 30 to 34.9 if they meet the criteria for specialist referral.12 Wegovy tablets don't have a confirmed NHS route yet, as NICE hasn't evaluated them separately for weight management.
- Mounjaro - licensed on the same private basis as Wegovy: a BMI of 30 or above, or from 27 with a weight-related condition.11 NHS prescribing follows NICE TA1026, with a phased rollout that currently prioritises adults with a BMI of 40 or above and at least four qualifying health conditions.13 A lower BMI threshold applies if you're from a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background.
- Orlistat - less restrictive criteria than the injections. The 120mg prescription strength is licensed for adults with a BMI of 30 or above, or from 28 with a weight-related risk factor, and it's more widely available through GPs.3 The 60mg version (Alli) can be bought over the counter by adults with a BMI of 28 or above, after a short pharmacist assessment.
None of these treatments are suitable during pregnancy or breastfeeding. You'll need a full clinical assessment to check for other reasons a treatment might not suit you before starting any of them.
Which weight loss treatment is right for you?
There's no single right answer. The decision should always be made with a prescriber, based on your health, goals and preferences. That said, a few general starting points can help narrow things down:
- Biggest average weight loss - if you're comfortable with a weekly injection, Mounjaro tends to produce the strongest results in clinical trials.
- A longer track record - Wegovy injections have been used for weight management for longer, and are a well-established alternative.
- Tablets over injections - if you can stick to a strict morning routine, Wegovy tablets offer broadly similar results to the injection.
- An earlier starting point - if you don't yet meet the BMI threshold for the GLP-1 medicines, or you'd rather start with an oral, non-hormonal option, orlistat may be more accessible.
Whichever option you're considering, medication works best as one part of a wider approach to diet, activity and habits. Relying on it as a standalone fix tends not to give the best long-term results.
When to seek further advice
Contact your GP or prescribing clinician if you:
- Develop severe or persistent nausea, vomiting, abdominal pain, or diarrhoea on any of these treatments
- Notice symptoms consistent with pancreatitis while taking Wegovy or Mounjaro: severe upper abdominal pain, particularly radiating to the back
- Notice signs of gallbladder problems: pain in the upper right abdomen, especially after fatty meals
- Are taking oral contraceptives and have recently started or increased your dose of Mounjaro
- Experience severe diarrhoea while taking orlistat and rely on the contraceptive pill, as its absorption may be reduced
- Have lost less than 5% of your starting body weight after six months on any treatment at the maximum tolerated dose
Do not stop any of these treatments without speaking to your prescriber first.
Frequently asked questions
Is Mounjaro better than Wegovy or orlistat for weight loss?
Clinical trial data suggests Mounjaro tends to produce the greatest average weight loss of the three, with reductions of up to 22.5% over 72 weeks in the SURMOUNT-1 trial, compared with up to around 19% for Wegovy's higher 7.2mg dose and a more modest 3 to 5% for orlistat.7,5,8 However, "better" depends on your individual circumstances, including your BMI, medical history, and whether you'd prefer an injection or a tablet. Mounjaro also has stricter eligibility criteria and a higher cost than orlistat.
Can I take orlistat together with Wegovy or Mounjaro?
There's no clinical evidence supporting the combined use of orlistat with a GLP-1 medicine, and this isn't something to do without your prescriber's guidance. If you're already taking orlistat and want to switch to Wegovy or Mounjaro, speak to your prescriber, who can assess your eligibility and guide you through the transition.
Which of these treatments can I get on the NHS?
Orlistat 120mg is available on the NHS for adults with a BMI of 30 or above, or from 28 with a weight-related health condition, and is more widely accessible than the injectable options.3 Wegovy and Mounjaro are both available on the NHS through specialist weight management services under NICE guidance (TA875 and TA1026 respectively), but access is currently limited to those with the highest clinical need.11,12 The Wegovy tablet and Foundayo don't yet have a confirmed NHS route.
What's the difference between the Wegovy injection and the Wegovy tablet?
Both contain the same active ingredient, semaglutide, and produce broadly comparable results.6 The main difference is how you take them: the injection is administered once a week using a pre-filled pen, while the tablet is taken once daily on an empty stomach, with a 30 minute gap before eating or drinking anything other than water. Some people find the tablet's timing rules more restrictive than a weekly injection.
Is Foundayo available in the UK yet?
Foundayo (orforglipron) received MHRA approval on 10 August 2026, but it isn't yet available to order, as stock still needs to be manufactured, imported and distributed through the UK supply chain.1 It isn't currently a like-for-like alternative to Mounjaro, Wegovy or orlistat, though this may change once it reaches UK pharmacies.
What happens if I stop taking Wegovy, Mounjaro or orlistat?
Weight regain is common after stopping any of these treatments if the underlying diet and lifestyle changes aren't maintained. With Wegovy and Mounjaro, the appetite-suppressing effects stop once injections stop, and hunger typically returns to baseline levels. Orlistat's effect also stops immediately on discontinuation, as it has no systemic action. In all cases, speak to your prescriber before stopping treatment.
Which has the fewest side effects?
Wegovy, Mounjaro and orlistat all commonly cause gastrointestinal side effects, but the nature of those effects differs. Wegovy and Mounjaro's side effects, such as nausea and diarrhoea, are systemic and tend to improve as your body adjusts.9,10 Orlistat's side effects, such as oily stools and flatulence, are directly caused by unabsorbed fat passing through the gut, and are more controllable through a low-fat diet.3 Neither profile is clearly "better" - it depends on which you find more manageable.
Can I switch between Wegovy, Mounjaro, the Wegovy tablet and Foundayo?
Any switch between GLP-1 medicines should only be made under the guidance of a registered prescriber, who can assess your treatment history and determine a suitable starting dose. Foundayo isn't yet available to order in the UK, so switching to it isn't currently an option regardless.
References
- Medicines and Healthcare products Regulatory Agency. UK first in Europe to authorise orforglipron for weight management and type 2 diabetes. GOV.UK; 10 August 2026. gov.uk
- Wharton S, et al. Orforglipron, an Oral GLP-1 Receptor Agonist for Obesity Treatment (ATTAIN-1). New England Journal of Medicine. 2025. doi:10.1056/NEJMoa2511774
- Roche Products Ltd. Xenical (orlistat 120mg) Summary of Product Characteristics. Electronic Medicines Compendium (eMC). medicines.org.uk/emc
- Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). New England Journal of Medicine. 2021;384(11):989-1002. doi:10.1056/NEJMoa2032183
- Wharton S, et al. Once-weekly semaglutide 7.2mg in adults with obesity (STEP UP). Lancet Diabetes & Endocrinology. 2025. doi:10.1016/S2213-8587(25)00226-8
- Wilding JPH, et al. Oral Semaglutide 25mg in Adults with Overweight or Obesity (OASIS 4). New England Journal of Medicine. 2025. doi:10.1056/NEJMoa2500969
- Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). New England Journal of Medicine. 2022;387(3):205-216. doi:10.1056/NEJMoa2206038
- Bhaskaran K, et al. Efficacy of orlistat in type 2 diabetes: a systematic review and meta-analysis. BJGP Open. 2025. doi:10.3399/BJGPO.2025.0058
- Aronne LJ, et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5). New England Journal of Medicine. 2025;393(1):26-36. doi:10.1056/NEJMoa2416394
- Novo Nordisk Ltd. Wegovy (semaglutide) Summary of Product Characteristics. Electronic Medicines Compendium (eMC). medicines.org.uk/emc
- Eli Lilly Nederland B.V. Mounjaro (tirzepatide) Summary of Product Characteristics. Electronic Medicines Compendium (eMC). medicines.org.uk/emc
- National Institute for Health and Care Excellence. Semaglutide for managing overweight and obesity (TA875). NICE; 2023. nice.org.uk/guidance/ta875
- National Institute for Health and Care Excellence. Tirzepatide for managing overweight and obesity (TA1026). December 2024. nice.org.uk/guidance/ta1026
This article is intended for informational purposes only and does not replace professional medical advice. Always read the patient information leaflet supplied with your medication and speak to a healthcare professional if you have specific concerns.