Orlistat vs Mounjaro and Wegovy: How They Differ, and Can You Take Them Together?

Short answer: Orlistat and Mounjaro or Wegovy work in different ways. Orlistat (Xenical 120mg on prescription, or alli 60mg from a pharmacy) is a capsule taken with meals that blocks the gut enzymes that digest fat, so some of the fat you eat is not absorbed; it is not a GLP-1, and its UK product information describes no effect on appetite (Xenical SmPC section 5.1). Mounjaro (tirzepatide) and Wegovy (semaglutide) are once-weekly injections that act on the appetite areas of the brain, through GLP-1, and GIP as well for Mounjaro (SmPC section 5.1 of each). We do not supply orlistat together with a GLP-1 medicine: our consultations ask about every weight-loss medicine you take, and our pharmacist confirms that one has stopped before the other is supplied. Who each may suit differs too: orlistat from a BMI of 30, or 28 with certain conditions, and Mounjaro or Wegovy from a BMI of 30, or 27 with a weight-related condition.

This guide sets out what the UK product information and the NHS say, and how our service works, as of October 2026: how each medicine works, whether orlistat affects appetite, why we do not supply them together, who each may suit, the side effects, how each is taken and how to change from one to the other. A GPhC-registered pharmacist reviews every Solira consultation before anything is supplied.

What is the difference between orlistat and Mounjaro or Wegovy?

The difference is where they work: orlistat works inside the gut, on the fat in your meals, while Mounjaro and Wegovy work on appetite. This is how the UK product information describes each, as of October 2026 (Xenical and alli SmPCs sections 4.1, 4.2 and 5.1; Mounjaro and Wegovy SmPCs sections 4.1, 4.2, 4.8 and 5.1):

The table does not rank them. Orlistat and the GLP-1 medicines were tested in different trials, in different groups of people, so their results are not a direct comparison, and which suits you depends on your health, your weight and your medicines. For Mounjaro and Wegovy side by side, see Mounjaro vs Wegovy, and for every licensed option, Mounjaro alternatives.

How does orlistat work?

Orlistat works by blocking lipases, the enzymes in your stomach and small intestine that break down fat, so part of the fat in each meal is not digested or absorbed and passes out of the body instead. The UK product information calls it "a potent, specific and long-acting inhibitor of gastrointestinal lipases" that works inside the stomach and small intestine (Xenical SmPC section 5.1). The NHS website puts it simply: about a third of the fat from your food is passed out in your poo. Our orlistat page gives about a third at 120mg and about a quarter at 60mg, from each product's patient leaflet.

This is how we counsel every orlistat patient to take it:

Take one capsule immediately before, during, or up to one hour after each main meal, up to three times a day. If you miss a meal, or a meal contains no fat, skip that dose.

Its effect starts and stops quickly. The amount of fat in your stools rises within 24 to 48 hours of a dose, and after stopping it usually returns to normal within 48 to 72 hours (Xenical SmPC section 4.2).

How do Mounjaro and Wegovy work?

Mounjaro and Wegovy work mainly through the brain, on appetite. Mounjaro contains tirzepatide, "a long acting GIP and GLP-1 receptor agonist": it acts on two hormone receptors, including in the areas of the brain important to appetite, and reduces appetite and how much you eat (Mounjaro SmPC section 5.1). More in how does Mounjaro work.

Wegovy contains semaglutide, a man-made version of GLP-1, a hormone your body releases after eating that regulates appetite and calorie intake. It acts directly on the hypothalamus and brainstem, which control hunger and fullness, so you feel less hungry and fuller (Wegovy SmPC section 5.1). More in what is Wegovy, and the whole class in what is a GLP-1 medication.

Does orlistat reduce appetite?

No. Orlistat is not an appetite suppressant and it is not a GLP-1: it works inside the gut, on the fat you eat, and the UK product information for both Xenical and alli describes no effect on appetite (SmPC sections 4.1, 4.2 and 5.1 of each, as of October 2026). It classes orlistat as a "peripherally acting" anti-obesity medicine, one that works in the stomach and small intestine rather than on the brain.

The weight-loss medicines that act on appetite are the GLP-1 medicines, such as Mounjaro and Wegovy, and the GLP-1 tablets, Wegovy tablets and Foundayo. With orlistat, the weight loss comes from the fat that is not absorbed, alongside a reduced-calorie diet, which is why the diet below is part of taking it.

Can you take orlistat with Mounjaro or Wegovy?

We do not supply orlistat together with Mounjaro, Wegovy or any other GLP-1 medicine. The rules our pharmacist works to for each of these medicines exclude taking another weight-loss medicine at the same time, whether prescribed, bought over the counter or herbal, and the orlistat rules count a GLP-1 medicine as another weight-loss medicine. The orlistat product information does not mention GLP-1 medicines at all (Xenical SmPC, revised October 2023), so it gives no guidance on using the two together, and we do not combine them.

This is how it works in our consultations, in both directions:

• Starting Mounjaro or Wegovy while on orlistat. Our weight-loss consultation asks whether you take any other weight-loss medicine, for example orlistat or alli. If you do, it says: "Weight-loss medicines are not taken together. Our pharmacist will confirm with you that it has stopped before anything is supplied."
• Asking for orlistat while on a GLP-1 medicine. Our orlistat consultation asks about every other weight-loss medicine, including any GLP-1 medicine as an injection or a tablet, and if you take one, it does not go on: we are unable to supply orlistat alongside it. If one of your diabetes medicines is a GLP-1, it says: "We can't supply orlistat alongside this medicine. Please speak to your GP or the clinic that prescribes it."
• A GLP-1 medicine from us recently. If we supplied you a GLP-1 medicine recently, our pharmacist confirms with you that it has stopped before orlistat is supplied.

The same applies to the GLP-1 tablets, Wegovy tablets and Foundayo. Other medicines that matter with Mounjaro and Wegovy are in medicines you cannot take with Mounjaro or Wegovy.

Who can have orlistat, and who can have Mounjaro or Wegovy?

Orlistat and the GLP-1 medicines have different eligibility rules: orlistat 120mg needs a BMI of 30 or above, or 28 or above with type 2 diabetes, high blood pressure or high cholesterol, while Mounjaro and Wegovy need a BMI of 30 or above, or 27 or above with a weight-related condition. These are the rules our pharmacist works to, as of October 2026:

The age ranges differ as well: orlistat 120mg is supplied to adults aged 18 to 75, and Mounjaro and Wegovy to adults aged 18 to 85. Orlistat is not suitable if you are pregnant, planning a pregnancy or breastfeeding, have chronic malabsorption syndrome, cholestasis, or liver or kidney problems, or your weight gain is caused by a hormone condition or a medicine. For Mounjaro and Wegovy, the product information gives one reason never to use them, an allergy to the medicine or its ingredients, and our consultation also asks about conditions where we do not supply them. The full list is in is Mounjaro safe? and is Wegovy safe?

How do the side effects compare?

Both mainly affect the stomach and bowel, but in different ways: orlistat's side effects come from the fat that is not absorbed, while with the GLP-1 medicines the most common are nausea, diarrhoea, vomiting and constipation. The orlistat product information says its side effects are "largely gastrointestinal in nature" and became less frequent the longer people took it (Xenical SmPC section 4.8).

With orlistat, common side effects include oily or fatty stools, oily spotting, wind with discharge, and needing the toilet urgently or more often. They are more likely after a meal high in fat. Side effects in the gut are more likely after a meal high in fat.

For Mounjaro, the product information lists nausea, diarrhoea, vomiting, constipation, stomach pain and reduced appetite as very common, affecting more than 1 in 10 people; for Wegovy, headache, nausea, vomiting, diarrhoea, constipation, stomach pain and tiredness. For both, stomach side effects happen most often while the dose is going up, and are mostly mild to moderate (SmPC section 4.8 of each). Pancreatitis is uncommon with both (up to 1 in 100 people) and gallstones are common (up to 1 in 10). The rates and how to manage each are in Mounjaro side effects and Wegovy side effects.

How are they taken day to day?

Orlistat is taken with meals, every day, while Mounjaro and Wegovy are a single injection once a week, so the routines are very different. With orlistat, the diet is part of the treatment. This is the counselling we give every orlistat patient:

Eat a balanced diet with slightly fewer calories, rich in fruit and vegetables, with about 30% of your calories from fat. Spread your fat, carbohydrate and protein over three main meals.

Take a daily multivitamin containing vitamin D, at least 2 hours after a dose of orlistat, or at bedtime.

Mounjaro and Wegovy are injected under the skin once a week, at any time of day, with or without meals (SmPC section 4.2 of each). A Mounjaro KwikPen and a Wegovy FlexTouch pen each hold four weekly doses (sections 6.5 and 6.6); Wegovy 7.2mg comes as single-dose pens, one a week. A reduced-calorie diet and more physical activity are part of the licence for both (SmPC section 4.1). Vitamins alongside a GLP-1 medicine are covered in vitamins and supplements on Mounjaro and Wegovy.

Both can affect the contraceptive pill, in different ways. For orlistat: If you experience severe diarrhoea, use an additional contraceptive method as orlistat may reduce the effectiveness of oral contraception.

Contraception (Mounjaro only): tirzepatide can reduce absorption of the contraceptive pill. Use a non-oral method or add condoms for 4 weeks after starting and for 4 weeks after each dose increase. Wegovy needs no extra precautions unless severe vomiting or diarrhoea occurs, then follow missed-pill guidance. More in GLP-1 medicines, contraception and pregnancy.

Can you switch from orlistat to Mounjaro or Wegovy, or back?

Yes, you can change from one to the other after a consultation, as long as the new medicine suits you: the one you are on stops before the other is supplied, and our pharmacist confirms that with you. This is how it goes:

1. Tell us what you take now. Our consultations ask about every weight-loss medicine, including orlistat or alli bought from a pharmacy, and every GLP-1 medicine, injection or tablet.

2. One stops before the other starts. Weight-loss medicines are not taken together. Our pharmacist will confirm with you that it has stopped before anything is supplied.

3. A pharmacist reviews it. A GPhC-registered pharmacist reviews your answers, and asks you anything else needed, before the new medicine is supplied.

Moving to a GLP-1 medicine, the dose starts low and rises in steps: if you have not taken them before, Mounjaro starts at 2.5mg once a week and Wegovy at 0.25mg, to make stomach side effects less likely (SmPC section 4.2 of each). Our Mounjaro dosage chart and Wegovy dose schedule set out each step.

Moving to orlistat, it has its own orlistat consultation and its own review point: Orlistat is reviewed at 12 weeks and only continued if you have lost at least 5% of your starting weight. After that, our pharmacist reviews it at every order. Each order through Solira is paid on its own, with no subscription to cancel when you change, as our guide to weight-loss medication without a subscription explains.

Is orlistat available on the NHS?

Yes. Orlistat can be prescribed on the NHS as Xenical for adults with a BMI of 30 or above, or 28 or above with a weight-related condition such as type 2 diabetes or high blood pressure, and a lower dose can be bought from a pharmacy as alli (NHS website, page last reviewed 6 May 2026). The NHS routes for Mounjaro and Wegovy are in weight-loss injections on the NHS.