What Is Orlistat and How Does It Work?

Orlistat is a gastrointestinal lipase inhibitor that works by blocking the absorption of 25% of the fat in a meal and is used for weight loss in overweight adults, 18 years and older when used along with a reduced-calorie and low-fat diet.

  • Orlistat is available under the following different brand names: Alli, and Xenical.

What Are Dosages of Orlistat?

Dosages of Orlistat:

Adult and Pediatric Dosage Forms and Strengths


  • 60 mg (Alli)
  • 120mg (Xenical)

Dosage Considerations – Should be Given as Follows:

Obesity Management

Indicated in patients with pretreatment BMI greater than 30 kg/m², or BMI greater than 27 kg/m² in presence of other risk factors or diseases (e.g., hypertension, diabetes mellitus, hyperlipidemia)


  • Rx (Xenical): 120 mg orally every 8 hours with each fat-containing meal (during or up to 1 hour after the meal), doses greater than 120 mg three times daily show no additional benefit
  • Over-the-Counter (OTC) (Alli): Up to 60 mg orally every 8 hours with each fat-containing meal

Children under 12 years: Safety and efficacy not established

Children 12 years and older:

  • Prescription (Rx) (Xenical): 120 mg orally every 8 hours with each fat-containing meal (during or up to 1 hour after the meal), doses greater than 120 mg three times daily show no additional benefit
  • Over-the-Counter (OTC) (Alli): Up to 60 mg orally every 8 hours with each fat-containing meal

Only effective as an adjunct to caloric restriction, increased physical activity, and behavioral modification

Also, see Administration and Cautions (drug interaction overview)

What Are Side Effects Associated with Using Orlistat?

Common side effects of Orlistat include:

  • Oily spotting on underwear

Other side effects of orlistat include:

  • Gas (flatulence) with discharge
  • Fatty/oily stools
  • Increased defecation
  • Fecal incontinence/inability to control bowel movements
  • Urgent bowel movements
  • Loose stools
  • Clay-colored stools
  • Diarrhea
  • Rectal pain
  • Nausea
  • Vomiting
  • Reduced absorption of fat-soluble vitamins and beta-carotene
  • Liver failure
  • Oxalate nephropathy
  • Leukocytoclastic vasculitis
  • Increased number of bowel movements
  • Stomach pain
  • Weakness
  • Dark urine
  • Itching
  • Loss of appetite
  • Yellowing of the skin or eyes (jaundice)
  • Problems with your teeth or gums
  • Cold symptoms (stuffy nose, sneezing, cough, fever, chills, sore throat, flu symptoms)
  • Headache
  • Back pain
  • Skin rash

This document does not contain all possible side effects and others may occur. Check with your physician for additional information about side effects.

What Other Drugs Interact with Orlistat?

If your doctor has directed you to use this medication, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider, or pharmacist first.

  • Orlistat has no known severe interactions with other different drugs.
  • Orlistat has no known serious interactions with other different drugs.
  • Orlistat has moderate interactions with at least 65 different drugs.
  • Orlistat has mild interactions with at least 21 different drugs.

This information does not contain all possible interactions or adverse effects. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share this information with your doctor and pharmacist. Check with your health care professional or doctor for additional medical advice, or if you have health questions, concerns, or for more information about this medicine.

What Are Warnings and Precautions for Orlistat?


This medication contains orlistat. Do not take Alli or Xenical if you are allergic to orlistat or any ingredients contained in this drug.

Keep out of reach of children. In case of overdose, get medical help or contact a Poison Control Center immediately.


Effects of Drug Abuse

Short-Term Effects

  • See "What Are Side Effects Associated with Using Orlistat?"

Long-Term Effects

  • See "What Are Side Effects Associated with Using Orlistat?"


  • If a meal is missed or contains no fat, the dose should be omitted.
  • Daily fat intake (30% of calories), carbohydrate, and protein should be evenly distributed over 3 main meals.
  • Note: A multivitamin supplement (including vitamins A, D, E, K) is recommended.
  • Postmarketing reports of severe liver injury with hepatocellular necrosis or acute hepatic failure with some cases resulting in liver transplant or death.
  • History of hyperoxaluria or calcium oxalate nephrolithiasis; cases of oxalate nephrolithiasis and oxalate nephropathy with renal failure have been reported.
  • Substantial weight loss can increase the risk of cholelithiasis.
  • Exclude organic causes of obesity (e.g., hypothyroidism), before prescribing therapy.
  • May increase gastrointestinal events when taking a diet high on fat (greater than 30% total daily calories from fat).
  • Diabetes mellitus.
  • Avoid with anorexia nervosa or bulimia.
  • Drug interaction overview:
    • Cyclosporine: Administer cyclosporine 3 hours after orlistat
    • Levothyroxine: Administer 4 hours apart; monitored for changes in thyroid function
    • Amiodarone oral: A pharmacokinetic study showed reduced amiodarone and desethylamiodarone systemic exposure when coadministered with orlistat
    • Antiepileptic drugs (AEDs): Convulsions reported with coadministration of AEDs and orlistat; monitor serum AED levels
    • Antiretroviral drugs: Loss of virological control has been reported in HIV-infected patients taking orlistat concomitantly with antiretroviral drugs; HIV RNA levels should be frequently monitored in patients taking orlistat and antiretroviral drugs; if HIV viral load increases, discontinue orlistat
    • Warfarin
      • Vitamin K absorption may be decreased with orlistat
      • Reports of decreased prothrombin increased INR and unbalanced anticoagulant treatment resulting in a change of hemostatic parameters have been with coadministration of orlistat and anticoagulants
      • Patients on chronic stable doses of warfarin or other anticoagulants who are prescribed orlistat should be monitored closely for coagulation parameters changes
    • Vitamin supplements
      • Orlistat may reduce the absorption of some fat-soluble vitamins and beta-carotene
      • Instruct patient to take a multivitamin containing fat-soluble vitamins to ensure adequate nutrition
      • Take the vitamin supplement at least 2 hours before or after taking orlistat, such as at bedtime

Pregnancy and Lactation

  • Do not use orlistat in pregnancy. The risks involved outweigh the potential benefits. Safer alternatives exist. Weight loss offers no potential benefit to a pregnant woman and may result in fetal harm. A minimum weight gain, and no weight loss, is currently recommended for all pregnant women, including those who are already overweight or obese.
  • It is not known if orlistat is distributed in breast milk. Orlistat is not recommended for use while breastfeeding.
Medscape. Orlistat.
RxList. Xenical Side Effects Drug Center.

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