Pharmacology · Anti-obesity drugs
Orlistat !
An anti-obesity drug that blocks fat-digesting enzymes in the gut, so part of the fat eaten leaves in the stool.
Updated 2026-11-01
Mechanism of action
Orlistat binds the active-site serine of gastric and pancreatic lipases in the gut lumen, forming a slowly reversible covalent bond. The lipases cannot split dietary triglycerides into absorbable fatty acids and monoglycerides, so part of the fat eaten is excreted. Fewer calories are absorbed; there is no effect on appetite.
- Binds gastric and pancreatic lipases in the gut lumen
- Dietary triglycerides are not split
- Part of the fat eaten leaves in the stool
- Fewer calories absorbed: modest weight loss
Pharmacokinetics
- Absorption
- Minimal absorption; it acts in the gut.
- Elimination
- Mostly in feces, unchanged.
Indications
- Obesity, for weight loss and maintenance with a reduced-calorie diet, and to reduce weight regain Obesity →
- Overweight with risk factors such as high blood pressure, diabetes or dyslipidemia Metabolic syndrome →
Adverse effects
Common
- Oily spotting, flatus with discharge
- Urgency, fatty or oily stools, more bowel movements
- Abdominal pain
Contraindications
- Pregnancy
- Chronic malabsorption syndrome
- Cholestasis
- Hypersensitivity to orlistat
Key interactions
- Cyclosporine
- Absorption falls; it is given hours after orlistat and levels are checked.
- Levothyroxine
- Absorption falls; doses are separated and thyroid function is watched.
- Warfarin
- Less vitamin K absorption can change the INR.
- Antiepileptic drugs
- Seizure control may change.
- Antiretroviral drugs
- Loss of viral control has been reported.
What is monitored
- Weight
- INR in patients on warfarin
- Thyroid function on levothyroxine
- Symptoms of liver injury
Administration and safety
- Oral capsule with each main meal that contains fat (during or shortly after).
- If a meal has no fat or is skipped, that dose can be skipped.
- A multivitamin with fat-soluble vitamins is taken at a different time of day, such as bedtime.
Nursing care
- Before: pregnancy, malabsorption, gallbladder or kidney stone history.
- During: bowel effects and fat intake; spreading fat over meals reduces symptoms.
- Teach to report itching, dark urine, jaundice or pale stools.
Pregnancy and breastfeeding
Contraindicated in pregnancy: weight loss is not a goal and offers no benefit.
Test yourself
Think of the answer, then tap the question to see it.
Why is a multivitamin given apart from orlistat?
Orlistat reduces absorption of fat-soluble vitamins; giving the vitamin at another time avoids the effect.
A patient on warfarin starts orlistat. What should be watched?
The INR, because less vitamin K is absorbed and the anticoagulant effect can change.
Name two contraindications to orlistat?
Pregnancy and chronic malabsorption (also cholestasis).
Related drugs
Related conditions
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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Orlistat: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); DailyMed - ORLISTAT capsule (DailyMed (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.