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Orlistat is a capsule swallowed 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 taken alongside a slightly reduced-calorie, lower-fat diet.
Orlistat 120mg vs. alli. This page covers the prescription-strength 120 mg capsule (Xenical) that Hi-Doctor’s doctors review. alli is the pharmacy version of orlistat that can be bought without a prescription — each alli capsule contains half the orlistat dose of the prescription-only 120 mg product. alli is centrally authorised across the EU, and the authorisation is held by Haleon Ireland Dungarvan Limited.

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What it is

Active ingredient

Orlistat — a lipase inhibitor taken as a hard capsule that acts only inside the gut.

Dosage

120 mg with each main meal, up to three capsules a day.
Orlistat is authorised in the EU for weight loss in adults with obesity, alongside a mildly reduced-calorie diet, and specifically for a body mass index of 28 kg/m² or more, taken together with a mildly reduced-calorie, lower-fat diet. It has been authorised for use in the EU since 29 July 1998, so a licensed doctor can prescribe it when it is clinically appropriate.

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How it works

It switches off fat-digesting enzymes

Orlistat blocks the enzymes in the stomach and gut that break down fat, so about a third of the fat in a meal passes through the body instead of being absorbed.

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 can take up. The fat 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 the body. The European Medicines Agency describes the 120 mg dose as letting about 30% of the fat eaten in a meal pass through undigested.
Unlike GLP-1 medicines, orlistat does not act on appetite — its effect depends on keeping to an appropriate diet while taking it. It is a valid alternative for people who cannot or do not want injectable treatments, although average weight loss is usually lower.

No injections

A capsule, not an injection.

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 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 (Diabetes Care 2004;27(1):155-161).
Every trial behind orlistat is grouped by source and evidence grade, so journal data and manufacturer announcements are not confused.

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Who it is not suitable for

A doctor checks medical history and current medication before prescribing. Yellowing skin can signal serious liver injury and should always be reported. Orlistat is not suitable for people with chronic malabsorption syndrome or cholestasis.

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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.

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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 at month 3 by the doctor, as the first meaningful assessment point.
Yes. Orlistat is authorised alongside a mildly reduced-calorie, lower-fat diet. The bowel 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

The EU Summary of Product Characteristics lists these bowel effects at the 120 mg dose: These bowel effects are more likely after a fatty meal, because the undigested fat has to go somewhere.
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.

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How Hi-Doctor handles it

A questionnaire covering weight, medical history, current medication and previous weight-loss treatment feeds into the doctor’s decision — see how eligibility works. Orlistat is one of several weight-loss options a doctor may consider, alongside injectable medicines like Mounjaro and Wegovy. For the 120 mg prescription version, see orlistat (Xenical). The medical consultation cost is set out on pricing; the medicine itself is paid separately at a pharmacy. See also safety and eligibility for the full checks a doctor applies.

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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.