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Orlistat is a capsule you swallow with meals. It is not a hormone and does not act on the brain or on appetite: it blocks the gut enzymes that digest fat, so roughly a third of the fat in a meal leaves the body in the stool instead of being absorbed. In the EU it is sold as Xenical and is taken alongside a slightly reduced-calorie, lower-fat diet.
Active ingredient orlistat  ·  Dosages 120 mg with each main meal  ·  Authorised in the EU since 29 July 1998

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What it is

Orlistat is a lipase inhibitor: it blocks the intestinal enzyme that digests fat, reducing the absorption of part of the fat you eat. Unlike GLP-1s, it does not act on appetite — its effect depends on keeping to an appropriate diet while taking it. It’s a valid alternative for people who cannot or do not want injectables, although average weight loss is usually lower.

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How it works

It switches off fat-digesting enzymes

Orlistat binds to lipases, the enzymes your stomach and small intestine release to digest fat. It forms a chemical bond with the active site of gastric and pancreatic lipase and switches the enzyme off inside the gut. It is not an appetite medicine and does not act on the brain.

Dietary fat stays undigested

The inactivated enzyme cannot break dietary fat, which arrives as triglycerides, into the smaller free fatty acids and monoglycerides that the gut wall is able to take up. The fat therefore stays whole, and whole fat molecules are too large to cross into the body.

The blocked fat leaves in stool

The unabsorbed fat passes along the bowel and out in the stool, so those calories never reach you. The EMA describes the 120 mg dose as letting about 30% of the fat eaten in a meal pass through undigested.

No injections

Taken as a hard capsule; it acts only inside the gut.

Local, not systemic

Acts locally in the gut, not system-wide.

Adjunct to diet

An alternative when GLP-1s aren’t the right fit.

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What the studies reported

XENDOS (Diabetes Care 2004;27(1):155-161) was designed to test prevention of type 2 diabetes rather than weight loss alone. Only 52% of the orlistat group and 34% of the placebo group completed the four years, and everyone in the trial also made lifestyle changes. The European Multicentre Orlistat Study (Lancet 1998;352(9123):167-172) is the other cited trial. Full prescribing detail is in the EMA EPAR for Xenical and its Summary of Product Characteristics (SmPC).

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Interactions

Because orlistat blocks fat absorption, it can interfere with the absorption of other medicines taken at the same time. The EU Summary of Product Characteristics advises that orlistat and cyclosporine should not be taken together, and that thyroid medicines, warfarin and some anti-epileptic medicines may need dose adjustment. The reviewing doctor checks current medication before prescribing.

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What happens when you stop

Because orlistat works only while it is in the gut, stopping means normal fat digestion resumes. Weight that was lost during treatment can be regained if the dietary changes made alongside it are not sustained. The reviewing doctor discusses a maintenance plan when treatment ends.

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Common questions

Orlistat and GLP-1 medicines work through completely different mechanisms — one in the gut, one through hormone signalling. A doctor reviews whether combining them is appropriate for your case, but the two are not routinely prescribed together.
The effect on fat absorption starts with the first capsule taken with a fatty meal. Weight change is reviewed by the doctor at month 3, the first meaningful assessment point.
Yes. Orlistat is authorised alongside a mildly reduced-calorie, lower-fat diet. Bowel side effects are more likely after a fatty meal, so adjusting meals towards lower fat from day 1 is part of the approach.
Orlistat can reduce absorption of vitamins A, D, E and K. The EU product information advises a diet rich in fruit and vegetables and says a multivitamin supplement taken at bedtime may be considered.
Orlistat has been authorised for use in the EU since 29 July 1998, with long-term safety data from the XENDOS trial that followed people for four years. The doctor reviews response at month 3 and periodically thereafter.

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What has been reported

Lower absorption of fat-soluble vitamins. Orlistat can reduce absorption of vitamins A, D, E and K; the EU product information advises a diet rich in fruit and vegetables and says a multivitamin supplement, taken at bedtime, may be considered.
Oily stools are very common. Yellowing skin can signal serious liver injury and needs urgent medical attention.

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How to take it

1

Days 1–7

Adjust meals towards lower fat.
2

Weeks 2–8

Consistent use with each main meal.
3

Month 3

Response reviewed by your doctor.
Take it with the meal — one 120 mg capsule with each main meal, up to three capsules a day. Skip meals that have no fat, since there is nothing for it to act on.

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How Hi-Doctor handles it

An EU-licensed doctor reviews your case and, if eligible, issues an electronic prescription valid at any EU pharmacy under Directive 2011/24/EU. See pricing for the consultation fee; the medicine is paid separately at a pharmacy. For injectable alternatives, see liraglutide, semaglutide, or tirzepatide. For the non-prescription version, see alli. The full eligibility checks are on safety and the weight-loss treatment area.

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Start a consultation

Weight-loss consultation

Answer the weight-loss questionnaire and a registered doctor reviews it. They decide whether treatment is appropriate, which one, and at what dose — and declining is a normal outcome. See what it costs and how the review works.
This page is reference information, not medical advice and not a prescription. Whether a medicine is appropriate for you is decided by a registered doctor after reviewing your consultation.