Orlistat vs GLP-1 Medications: How They Compare

Orlistat and GLP-1 medicines such as Mounjaro (tirzepatide) and Wegovy (semaglutide) are both licensed in the UK for weight management, but they work in completely different ways and differ greatly in how much weight people lose on average. Orlistat is a capsule that stops some dietary fat being absorbed. GLP-1 medicines reduce appetite through hormone pathways. In trials, GLP-1 medicines produced several times more average weight loss than orlistat, but orlistat is older, widely available on the NHS, and suits some people. This guide compares the two so you can discuss them with a prescriber.

Two very different medicines

Orlistat in brief

Orlistat has been used for weight management in the UK since the late 1990s. It is a lipase inhibitor: it blocks lipases, the enzymes in the stomach and small intestine that break down dietary fat. Fat that is not broken down cannot be absorbed and passes out of the body in the stools. At the prescription dose, roughly a third of the fat in a meal is not absorbed.

It comes in two strengths:

• 120mg capsules (brand name Xenical, and generic orlistat): prescription-only, usually taken up to three times a day with each main meal containing fat.
• 60mg capsules (brand name Alli): a pharmacy medicine, which a pharmacist can supply without a prescription after checking it is suitable, for adults with a BMI of 28 or more.

Orlistat acts locally in the gut and very little is absorbed into the bloodstream. It does not reduce appetite.

GLP-1 medicines in brief

GLP-1 receptor agonists copy the action of glucagon-like peptide-1, a hormone released by the gut after eating. They act on receptors in the brain to reduce hunger and increase feelings of fullness, and they slow the rate at which the stomach empties. Tirzepatide (Mounjaro) also acts on the GIP receptor. The result is that people tend to eat less without the same struggle against hunger.

The GLP-1 medicines licensed for weight management in the UK at the time of writing include:

• Mounjaro (tirzepatide), a weekly injection
• Wegovy (semaglutide), a weekly injection
• Liraglutide (Saxenda and generic versions), a daily injection
• Wegovy tablets (oral semaglutide), a daily tablet authorised by the MHRA in June 2026
• Foundayo (orforglipron), a daily tablet authorised by the MHRA in August 2026

All are prescription-only. For background, see our complete guide to Mounjaro and complete guide to Wegovy.

At a glance

What the evidence shows

Orlistat

The largest long-term orlistat trial is XENDOS, published in Diabetes Care in 2004. It followed over 3,000 adults with obesity for four years, all receiving lifestyle advice. Those taking orlistat 120mg three times a day lost more weight on average than those on placebo (around 5.8kg compared with 3.0kg at four years), and the orlistat group had a lower rate of developing type 2 diabetes over the trial. Many participants did not complete the four years, which is common in long weight-management trials.

Shorter trials and pooled analyses have found broadly similar results: orlistat adds a few kilograms of weight loss on top of diet and lifestyle changes over a year. That is modest, but for some people it is clinically meaningful, particularly alongside improvements in blood pressure, cholesterol or blood glucose.

GLP-1 medicines

The main weight-management trials for GLP-1 medicines produced considerably larger average results:

For a person weighing 100kg, a 15% reduction would be 15kg, which illustrates the difference in scale compared with orlistat. These are averages, though. Some people lose much more and some much less, and you can read about the spread in our guide to realistic weight loss expectations.

Side effects compared

Orlistat

Orlistat's side effects follow directly from how it works. Undigested fat in the bowel can cause:

• Oily spotting from the bottom
• Wind with an oily discharge
• Urgent need to open the bowels, sometimes with little warning
• Fatty or oily stools
• More frequent bowel movements
• Abdominal discomfort

These are more likely after meals high in fat. Many people find the effects encourage them to eat less fat, which is part of how orlistat is thought to help. The SmPC also notes that orlistat can reduce absorption of fat-soluble vitamins (A, D, E and K), and a multivitamin taken at bedtime, away from the orlistat dose, is often advised. Rare but serious problems, including liver injury, have been reported.

Orlistat can interact with several medicines, including levothyroxine, ciclosporin, warfarin and other anticoagulants, some anti-epilepsy medicines, amiodarone and some antiretroviral medicines. Severe diarrhoea can also reduce the effectiveness of the oral contraceptive pill. A pharmacist should always check your other medicines.

GLP-1 medicines

GLP-1 medicines most commonly cause:

• Nausea, especially early on and after dose increases
• Vomiting
• Diarrhoea or constipation
• Indigestion, burping, reflux and bloating
• Tiredness and headache
• Injection-site reactions (injections only)

Less common but serious risks include pancreatitis, gallbladder problems such as gallstones, and dehydration leading to kidney problems. Low blood sugar can occur in people also taking insulin or sulfonylureas. The MHRA has advised effective contraception during treatment, and has noted that tirzepatide may reduce the effectiveness of oral contraceptives in some people. Our guides to Mounjaro side effects and Wegovy side effects cover these in detail.

A practical difference

The two sets of side effects affect daily life in different ways. Orlistat side effects are tied to individual meals and can be reduced by eating less fat. GLP-1 side effects are more related to the medicine itself and tend to ease as the body adjusts, though some people continue to have them.

Who is eligible?

Orlistat

NICE guidance on overweight and obesity management (NG246, 2025) includes orlistat as an option for adults alongside diet, physical activity and behavioural support. The usual criteria for the prescription strength are a BMI of 30 or more, or 28 or more with weight-related risk factors. Lower BMI thresholds are often applied for people from some ethnic backgrounds. NICE advises reviewing orlistat after 12 weeks and using clinical judgement about stopping if a person has not lost at least 5% of their starting weight.

The pharmacy strength (Alli) is for adults with a BMI of 28 or more, after a pharmacist consultation.

GLP-1 medicines

UK licences for GLP-1 weight-management medicines usually cover adults with a BMI of 30 or more, or 27 or more with at least one weight-related condition, alongside a reduced-calorie diet and increased physical activity. Private prescribers generally work to these licence criteria.

NHS access is narrower:

• Wegovy is recommended by NICE (TA875) for some people within specialist weight-management services, for up to two years.
• Mounjaro is recommended by NICE (TA1026), and NHS England began a phased rollout in primary care in June 2025, starting with people with the highest BMI and several weight-related conditions.

Our guides to who can get weight loss injections and private vs NHS weight loss treatment explain these routes in more depth.

Who might each option suit?

These are general considerations only. A prescriber will look at your full history.

Situations where orlistat may be discussed

• Wanting a medicine that acts locally in the gut with little absorption into the body
• A BMI that is above the threshold for orlistat but where GLP-1 treatment is not suitable or not accessible
• A history that rules out GLP-1 medicines, such as previous pancreatitis or certain thyroid cancers (although orlistat has its own cautions)
• Preferring a capsule over an injection, where GLP-1 tablets are not suitable
• Wanting to try a first-line medicine alongside lifestyle changes, particularly through the NHS

Situations where a GLP-1 medicine may be discussed

• A higher BMI with weight-related conditions such as type 2 diabetes, high blood pressure or sleep apnoea
• Having tried orlistat without enough benefit
• Persistent hunger that makes dietary change hard to sustain
• Established cardiovascular disease, where semaglutide has outcome evidence from the SELECT trial (see Wegovy and heart health)

Who should not take orlistat

Orlistat is not suitable for people with chronic malabsorption syndromes or cholestasis (reduced bile flow), and is generally avoided during pregnancy and breastfeeding. For GLP-1 contraindications, see our guide to who should not take GLP-1 medications.

Living with each treatment

Orlistat day to day

• A capsule is taken with each main meal containing fat, or up to an hour after. If a meal is missed or contains no fat, the dose is usually skipped.
• Fat intake is ideally spread across three meals, with each meal containing a moderate amount.
• A multivitamin at bedtime is often recommended.
• People often learn quickly which meals trigger side effects.

GLP-1 medicines day to day

• Weekly injections are taken on the same day each week; daily tablets at a set time, with oral semaglutide on an empty stomach.
• Doses start low and rise gradually over several months.
• Smaller meals, eating slowly and stopping when full help reduce nausea.
• Adequate protein and fluids matter, especially as appetite falls. See protein on GLP-1 medication.

What happens when you stop?

With both treatments, weight tends to return after stopping if the habits and circumstances that led to weight gain have not changed. For GLP-1 medicines, this has been studied directly. In STEP 4 (semaglutide) and SURMOUNT-4 (tirzepatide), people who were switched to placebo after an initial period on the medicine regained a substantial part of the weight they had lost, while those who continued kept losing or maintained their loss. Our guide to weight regain after stopping GLP-1 medication explains this research.

Obesity is increasingly viewed as a long-term condition, and both NICE and prescribers now think about weight-management medicines in terms of ongoing treatment and support, not a one-off course.

Cost considerations

We do not quote prices in our guides. In general:

• Orlistat on NHS prescription is covered by the standard prescription charge in England, or is free in Scotland, Wales and Northern Ireland and for those with exemptions. Pharmacy and private costs vary.
• GLP-1 medicines privately cost considerably more, and prices depend on the medicine, the dose, the provider and what is included, such as clinical support and delivery. Manufacturer list prices also change; the UK list price of Mounjaro rose in September 2025, for example.

For current comparisons, see our prices page.

Why such a large difference in effect?

The gap in average weight loss between orlistat and GLP-1 medicines comes down to how each works.

Orlistat affects only one part of what we eat: fat. It does nothing to reduce hunger, and the body may partly compensate, for example if people eat more carbohydrate. Its side effects can encourage a lower-fat diet, which is helpful, but the overall effect on energy intake is limited.

GLP-1 medicines act on the brain's appetite systems. People typically report feeling full sooner, thinking about food less and finding it easier to stop eating. That leads to a sustained reduction in total energy intake, from every type of food. Tirzepatide's additional action on the GIP receptor appears to add to this effect, which may explain its larger average weight loss in trials.

This does not make orlistat "useless". For some people, a modest weight loss of 5% or so brings meaningful improvements in blood pressure, blood glucose and joint pain. NICE continues to include orlistat as an option for this reason.

Common misunderstandings

"Orlistat lets me eat what I like." No. Eating high-fat meals on orlistat greatly increases side effects. It works with a reduced-calorie, lower-fat diet, not instead of one.

"GLP-1 medicines replace the need for lifestyle changes." No. All UK licences for GLP-1 weight-management medicines specify use alongside a reduced-calorie diet and increased physical activity, and the trials included lifestyle support. Nutrition and strength training are particularly important to protect muscle as weight falls; see preserving muscle on GLP-1 treatment.

"Orlistat is safer because you can get it without a prescription." The pharmacy strength is available after a pharmacist consultation because its risks are considered manageable in that setting, but it still has side effects, interactions and people for whom it is unsuitable. Every medicine has risks as well as benefits.

"A GLP-1 tablet is the same kind of medicine as orlistat." No. GLP-1 tablets such as Wegovy tablets and Foundayo work on appetite hormones, like GLP-1 injections. They share nothing with orlistat except that they are swallowed. Our guide to weight loss tablets in the UK explains each option.

"Herbal or 'natural' alternatives work like these medicines." Products marketed as natural alternatives to GLP-1 medicines or orlistat have not been shown to produce comparable effects in robust trials, and some unlicensed products have been found to contain undeclared medicines. Be cautious of online claims.

Questions to ask your prescriber

• Based on my BMI and health, which options am I eligible for, privately and on the NHS?
• What average weight loss could I realistically expect, and how will we measure progress?
• How do the side effects of each option fit with my lifestyle and other conditions?
• Do any of my current medicines interact with orlistat or a GLP-1 medicine?
• If the first option does not work well enough, what would we try next?
• How long would treatment continue, and what support is available alongside it?

Can orlistat and GLP-1 medicines be used together?

There is little robust evidence for routinely combining orlistat with a GLP-1 medicine, and it is not a standard approach in UK guidance. Both medicines can cause bowel symptoms, which may add up. If you are taking orlistat and are being assessed for a GLP-1 medicine, tell the prescriber. They will usually stop one before starting the other. Never combine weight-loss medicines on your own.

When to speak to a professional

Talk to your GP, pharmacist or prescriber before starting either type of medicine, and if you are considering moving from orlistat to a GLP-1 medicine. Mention all the medicines you take, including thyroid medicines, anticoagulants, anti-epilepsy medicines and contraceptives. Tell them if you are pregnant, planning pregnancy or breastfeeding, or have a history of pancreatitis, gallbladder disease, liver or kidney problems, or an eating disorder.

Seek urgent medical help through NHS 111, or call 999 in an emergency, if you have:

• Severe, persistent abdominal pain, possibly spreading to the back, with or without vomiting
• Yellowing of the skin or eyes, dark urine, pale stools or itching (possible liver or gallbladder problems)
• Vomiting or diarrhoea that stops you keeping fluids down, or signs of dehydration
• Rectal bleeding or black, tarry stools
• Signs of a severe allergic reaction, such as swelling of the face or throat or difficulty breathing

You can report suspected side effects through the MHRA Yellow Card scheme. For more on the tablet options available in the UK, see our guide to weight loss tablets and the oral GLP-1 hub. To compare regulated online services, visit our provider comparison.