Pancreatic lipase inhibitor Pregnancy: Contraindicated in pregnancy — no clinical data on exposed pregnancies are available, although animal studies do not indicate direct or indirect harmful effects with respect to pregnancy, embryonal/foetal development, parturition or postnatal development. Contraindicated during breast-feeding, as it is not known whether orlistat is secreted into human milk. Women of childbearing potential: an additional contraceptive method is recommended to prevent possible failure of oral contraception in the case of severe diarrhoea. Animal studies do not indicate harmful effects on fertility.

Orlistat

Brand names: Xenical, Alli

Orlistat is an oral lipase inhibitor used as an adjunct to a reduced-calorie, lower-fat diet for the management of obesity and overweight with associated risk factors.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: One 60 mg capsule three times daily

Route: Oral — the capsule should be taken with water immediately before, during or up to 1 hour after each main meal. If a meal is missed or contains no fat, the dose should be omitted

Frequency: Three times daily, with each main meal

Max: No more than three 60 mg capsules should be taken in 24 hours

STRENGTH CAVEAT — the UK SPC retrieved is for alli 60 mg hard capsules (the lower-strength, pharmacy product). The 120 mg prescription strength has a separate SPC that was NOT fetched; do not extrapolate this regimen to it. Diet and exercise are important parts of a weight loss programme and a diet and exercise programme should be started before beginning treatment. While taking orlistat the patient should be on a nutritionally balanced, mildly hypocaloric diet containing approximately 30% of calories from fat (e.g. in a 2,000 kcal/day diet this equates to less than 67 g of fat), with the daily intake of fat, carbohydrate and protein distributed over three main meals. The diet and exercise programme should be continued after treatment stops. DURATION: treatment should not exceed 6 months; if patients have been unable to lose weight after 12 weeks of treatment they should consult their doctor or pharmacist and it may be necessary to discontinue. A multivitamin supplement should be taken at bedtime because orlistat may impair the absorption of fat-soluble vitamins (A, D, E and K). ELDERLY (65 years or over): data are limited, but as orlistat is minimally absorbed no dose adjustment is necessary. HEPATIC/RENAL IMPAIRMENT: not studied, but as orlistat is minimally absorbed no dose adjustment is necessary. PAEDIATRIC: safety and efficacy in children below 18 years of age has not been established and no data are available. US OTC labelling cross-check (ALLI): for overweight adults 18 years and older, take 1 capsule with each meal containing fat, do not take more than 3 capsules daily, use with a reduced-calorie low-fat diet and exercise programme, and take a multivitamin once a day at bedtime.

Dose adjustments

Renal

The effect of orlistat in individuals with renal (or hepatic) impairment has not been studied; however, as orlistat is minimally absorbed, no dose adjustment is necessary. Patients with kidney disease should consult a doctor before starting treatment, as orlistat use may be associated with hyperoxaluria and oxalate nephropathy leading sometimes to renal failure — the risk is increased in patients with underlying chronic kidney disease and/or volume depletion.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients
Concurrent treatment with ciclosporin
Chronic malabsorption syndrome
Cholestasis
Pregnancy and breast-feeding
Concurrent treatment with warfarin or other oral anticoagulants

Side effects

Gastrointestinal (very common) — oily spotting, flatus with discharge, faecal urgency, fatty oily stool, oily evacuation, flatulence, soft stools
Gastrointestinal (common) — abdominal pain, faecal incontinence, liquid stools, increased defaecation; mostly mild and transient, occurring early in treatment (within 3 months)
Mild rectal bleeding; diverticulitis and pancreatitis (frequency not known)
Hepatitis that may be serious (some fatal cases or cases requiring liver transplantation reported), cholelithiasis, increases in transaminases and alkaline phosphatase (frequency not known)
Hypersensitivity reactions including anaphylaxis, bronchospasm, angioedema, pruritus, rash and urticaria; oxalate nephropathy that may lead to renal failure; anxiety (common)

Interactions

Ciclosporin — concurrent treatment is contraindicated
Warfarin and other oral anticoagulants — concurrent treatment is contraindicated; decreased prothrombin and increased INR have been reported
Fat-soluble vitamins (A, D, E and K) — absorption may be impaired; a multivitamin supplement should be taken at bedtime
Levothyroxine — hypothyroidism and/or reduced control of hypothyroidism may occur; the two may need to be taken at different times and the levothyroxine dose may need adjustment
Amiodarone, antiepileptic medicinal products (monitor for changes in the frequency and severity of convulsions; consider administering at different times) and antiretrovirals for HIV (absorption may be reduced) — medical advice should be sought before concomitant use
Oral contraceptives — an additional contraceptive method is recommended to prevent possible failure in the case of severe diarrhoea. Antidiabetic, antihypertensive and lipid-lowering medicines may need dose adjustment as weight loss improves metabolic control, blood pressure and cholesterol

Clinical monograph

How it works

It inhibits gastric and pancreatic lipases within the gastrointestinal tract, reducing the breakdown and absorption of dietary fat, which is then excreted.

Prescribing in practice

Gastrointestinal effects such as oily stools, faecal urgency and flatulence are common and are worsened by a high-fat diet, so a lower-fat diet is essential.
It can reduce absorption of fat-soluble vitamins, so a multivitamin taken at bedtime is often recommended.
It may reduce absorption of some medicines, including ciclosporin, levothyroxine and certain antiepileptics, and may affect oral contraception if severe diarrhoea occurs.

Monitoring

Monitor weight response and review at intervals, continuing only if a meaningful weight loss is achieved within the recommended period.

Counselling the patient

Follow a reduced-fat diet to gain benefit and minimise the unpleasant gastrointestinal effects.
Take a multivitamin at bedtime to maintain fat-soluble vitamin intake.
Use additional contraceptive precautions if severe diarrhoea occurs, and separate from levothyroxine dosing.

Evidence & guidelines

Orlistat is recommended by NICE as a pharmacological adjunct to lifestyle measures in obesity when defined weight-loss targets are met.

Reference: NICE CG189; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways