If you're looking at options for medical weight loss in the UK, you'll be familiar with three names: Wegovy, Mounjaro and orlistat. Now, as of 2026, there are further oral weight loss medications that have been approved in the UK, meaning more options to consider.
This guide compares Wegovy injections, the newer Wegovy tablets, Mounjaro, Foundayo (the latest oral weight loss drug to be approved in the UK) and orlistat on how they work, how much weight you might lose, their side effects, and who's eligible for each in the UK.
How does each weight loss treatment work?
Although all the treatments support weight management, they work through different mechanisms, which is part of why their results and side effects differ from one to another.
Wegovy (semaglutide)
Wegovy contains semaglutide, a medicine that mimics GLP-1 (glucagon-like peptide-1) - a hormone your gut releases after eating. By activating GLP-1 receptors, it helps you feel fuller for longer, slows the rate at which food leaves your stomach, and reduces the frequency and intensity of food cravings. It's taken as a once-weekly injection using a pre-filled pen, with the dose gradually increased up to a maintenance dose of 2.4mg, or 7.2mg for those who need additional support after reaching the standard dose.
Wegovy tablets (oral semaglutide)
Wegovy tablets contain the same active ingredient as the injection (semaglutide) but in a once-daily tablet form. Because semaglutide is a peptide that would normally be broken down by stomach acid, the tablet must be taken on an empty stomach with a small amount of water, followed by a 30 minute gap before eating, drinking anything else, or taking other oral medicines. The dose starts at 1.5mg and is increased monthly through 4mg and 9mg to a maintenance dose of 25mg. Our Wegovy tablets dosage guide covers the full titration 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). Activating both receptors produces a stronger appetite-reducing effect than medicines that target GLP-1 alone, which is part of why Mounjaro tends to produce greater average weight loss in clinical trials. It's taken as a once-weekly injection, starting at 2.5mg and increased every four weeks up to a maximum of 15mg.
Foundayo (orforglipron)
Foundayo (orforglipron) is made by Eli Lilly, the same manufacturer behind Mounjaro. It's a newly approved oral GLP-1 tablet that received MHRA authorisation on 10 August 2026.1 Unlike Mounjaro, Foundayo targets GLP-1 alone rather than GLP-1 and GIP together. In its main trial, it produced a more modest average weight loss of around 12.4% over 72 weeks, but does not require an injection and has no restrictions on eating or drinking like Wegovy tablets.2 It isn't yet available to order in the UK, as stock is still being manufactured and distributed, so it isn't a direct alternative to Mounjaro today. If you're curious how it compares with Wegovy's own tablet, our Foundayo vs Wegovy pill guide has the details.
Orlistat
Orlistat works completely differently from the other options here. Rather than affecting appetite or hormone signalling, it blocks around a third of the fat in your food from being absorbed by inhibiting gastric and pancreatic lipase, the enzymes responsible for breaking down dietary fat.3 That undigested fat passes through the gut and out in your stool. It's taken as a capsule, usually three times a day with meals that contain fat, and is available on prescription (120mg) or over the counter at a lower dose (60mg, branded Alli).
How much weight can you lose with each treatment?
Clinical trial results aren't a guarantee of what you'll personally lose, but they give a useful sense of scale when comparing options. All figures below come from placebo-controlled trials in which participants also followed a reduced-calorie diet and increased physical activity.
- 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 the standard 2.4mg dose.5
- Wegovy tablets (25mg) - an average of 13.6% over 64 weeks when accounting for 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 respectively, over 72 weeks.7
- Foundayo - not yet available to order in the UK, but worth noting for context. In the ATTAIN-1 trial, participants 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 - typically produced a result of around 3% to 5% of starting body weight in real-world use - a systematic review of randomised controlled trials found orlistat produced an average of 2.4kg more weight loss than placebo alongside diet and exercise.8
None of these medicines have been tested head-to-head in the same trial, so treat the figures above as a general guide rather than a direct comparison. Individual results depend on your starting weight, dose, and how consistently you follow the accompanying diet and exercise advice.
How do the side effects compare?
The side effect profile is 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 gastrointestinal and classified as very common, meaning they affect more than 1 in 10 people:9,10
- Nausea - most noticeable in the early weeks of treatment or after a dose increase.
- Diarrhoea and vomiting - usually improve as your body adjusts.
- Constipation - increasing fibre and fluid intake can help.
- Decreased appetite - the intended effect, but can feel pronounced for some people.
More serious but less common risks include acute pancreatitis, gallbladder problems (including gallstones, which can occur more often during rapid weight loss), and acute kidney injury as a result of severe dehydration. Mounjaro and Wegovy also slow the rate at which food leaves your stomach, which can reduce the absorption of oral medicines, including the combined contraceptive pill. If you take oral contraception, use an additional barrier method for four weeks after starting treatment or after each dose increase.
Our dedicated Mounjaro side effects and Wegovy tablet side effects guides go into more detail.
Orlistat
Orlistat's side effects are almost entirely gastrointestinal and directly related to the amount of unabsorbed fat passing through your gut: oily or fatty stools, oily spotting, increased bowel movements, flatulence, and in some cases faecal urgency.3 These are more likely after a high-fat meal and tend to ease as you become more consistent about keeping dietary fat intake down.
Orlistat also reduces the absorption of fat-soluble vitamins (A, D, E and K). A daily multivitamin, such as OneVit Complete Multivitamin, taken at least two hours before or after your orlistat dose, is commonly recommended to help maintain adequate vitamin levels during treatment.3 Our orlistat side effects guide covers the full list.
Who is eligible for each treatment in the UK?
Licensed private eligibility for the GLP-1 medicines is broadly similar, though NHS access is far more restrictive and differs between them.
- Wegovy (injection and tablets) - licensed for adults with a BMI of 30 or above, or from 27 where at least one weight-related health condition is present.9 NHS access under NICE guidance (TA875) is limited to specialist weight management services for adults with a BMI of 35 or above, or 30 to 34.9 with a qualifying condition.11 The Wegovy tablet doesn't yet have a confirmed NHS route, as NICE hasn't separately evaluated it for weight management.
- Mounjaro - licensed on the same private basis as Wegovy: BMI of 30 or above, or from 27 with a weight-related condition.10 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.12 A lower BMI threshold applies for people from South Asian, Chinese, other Asian, Middle Eastern, Black African, or African-Caribbean backgrounds.
- Orlistat - has less restrictive criteria than the injectable options. 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 is more widely available through GPs.3 The 60mg version (Alli) can be bought over the counter for adults with a BMI of 28 or above, following a brief pharmacist assessment.
None of these treatments are suitable during pregnancy or breastfeeding, and a full clinical assessment is needed to check for other contraindications before starting any of them.
Which weight loss treatment is right for you?
There's no single right answer, and the decision should always be made with a prescriber based on your health, goals and preferences. That said, some general starting points can help narrow things down:
- If you want the greatest average weight loss and are comfortable with a weekly injection, Mounjaro tends to produce the strongest results in clinical trials.
- If you'd prefer an injection with a longer safety record, or want a slightly gentler option than Mounjaro, Wegovy is a well-established alternative.
- If tablets suit your routine better than injections, but you can manage a strict morning routine, the Wegovy tablet offers broadly comparable results to the injection.
- If you're at an earlier stage of weight management, don't yet meet the BMI threshold for the GLP-1 medicines, or would rather start with an oral, non-hormonal option, orlistat may be a more accessible starting point.
Whichever option you're considering, using medication as one part of a broader approach to diet, physical activity and habit change tends to produce the best long-term results, rather than relying on it as a standalone solution.
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 Wegovy or 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
- 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.