[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Anti-obesity drugs](https://durgical.com/en/pharmacology/classes/anti-obesity-drugs/) › Orlistat

[Pharmacology](https://durgical.com/en/pharmacology/) · [Anti-obesity drugs](https://durgical.com/en/pharmacology/classes/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

- Class: [Anti-obesity drugs](https://durgical.com/en/pharmacology/classes/anti-obesity-drugs/)
- Enzyme: Pancreatic and gastric lipases
- ATC code: A08AB01

## 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 →](https://durgical.com/en/conditions/obesity/)
- Overweight with risk factors such as high blood pressure, diabetes or dyslipidemia [Metabolic syndrome →](https://durgical.com/en/conditions/metabolic-syndrome/)

## Adverse effects

### Common

- Oily spotting, flatus with discharge
- Urgency, fatty or oily stools, more bowel movements
- Abdominal pain

### Serious (rare, important)

- Severe liver injury (rare)
- Oxalate kidney stones and oxalate nephropathy
- Deficiency of fat-soluble vitamins

## 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.

## Memory aid

Orlistat 'locks the lipase': fat that is not digested is not absorbed, it leaves, and so do some fat-soluble vitamins (A, D, E, K).

## 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).

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/orlistat/)

## Related drugs

- [Semaglutide](https://durgical.com/en/pharmacology/semaglutide/)
- [Liraglutide](https://durgical.com/en/pharmacology/liraglutide/)
- [Tirzepatide](https://durgical.com/en/pharmacology/tirzepatide/)

## Related conditions

- [Obesity](https://durgical.com/en/conditions/obesity/)
- [Metabolic syndrome](https://durgical.com/en/conditions/metabolic-syndrome/)

[← Back to the class: Anti-obesity drugs](https://durgical.com/en/pharmacology/classes/anti-obesity-drugs/)

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](https://medlineplus.gov/druginfo/meds/a601244.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [DailyMed - ORLISTAT capsule](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f81dfaeb-46d5-47ce-9ef6-19259f5ac61c) (DailyMed (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=A08AB01) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/orlistat/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/orlistat/