Xenical (orlistat): uses, doses, side effects

Steve Silvestro, MD - Contributor Avatar

Written by Alison Dalton 

Steve Silvestro, MD - Contributor Avatar

Written by Alison Dalton 

last updated: Nov 17, 2021

3 min read

There are many weight-loss drugs on the market. Most work by decreasing your appetite so that you’re more likely to eat smaller meals. Xenical (also known by its generic name, orlistat, and its over-the-counter name, Alli) is different. It works by reducing the amount of fat your body absorbs from the food you eat. Read on to learn about the effectiveness, benefits, dosage, and possible risks of Xenical.

What is Xenical (orlistat)?

Xenical is a weight-loss drug for people with obesity. It’s available only by prescription. The generic name for Xenical is orlistat. Xenical works by reducing the amount of fat your body absorbs from the foods you eat.

A lower-dose, over-the-counter (OTC) version of Xenical is available without a prescription. Its brand name is Alli.

Xenical uses

The FDA approves Xenical for the treatment of obesity. It can be used for weight loss, as well as weight management once you’ve lost weight. It is best used when combined with a reduced-calorie diet (National Library, 2020). 

Does Xenical work for losing weight? 

Xenical has been shown to be effective in lowering body weight, body mass index (BMI), and waist circumference. Studies showed that one year of using Xenical could result in losing 5–10% or more of your starting weight (FDA, 2009).

There can be other benefits of Xenical as well, including (Bansal, 2020):

Xenical should be combined with a reduced-calorie diet to be most effective.

Orlistat side effects

Common side effects of orlistat include (National Library, 2020):

  • Stomach cramps

  • Gas

  • Diarrhea

  • Stool leakage

  • Oily stools

These side effects are more likely to happen if you take Xenical with a high-fat meal (that is, more than 30% of the calories are from fat). If you avoid eating a lot of dietary fats with a meal, you may be less likely to have these side effects.

Some people taking Xenical have reported severe liver injury. However, it’s not known whether Xenical caused the damage.

Xenical dosage

Xenical comes in 120 mg capsules. The typical recommended dose of Xenical is one capsule three times per day, taken with your main meals, though your healthcare provider will determine the best plan for you. It’s recommended that no more than 30% of the calories in the meal come from fat. Because Xenical works by decreasing how much fat your body absorbs from a meal, you can skip the dose for that meal if the meal contains no fat. Increasing the dosage of Xenical doesn’t increase weight loss.

When using Xenical, you should take a multivitamin supplement that contains the fat-soluble vitamin A, vitamin D, vitamin E, vitamin K, and beta-carotene to ensure you’re getting all the nutrition you need. The multivitamin should be taken at least two hours before or after taking Xenical (National Library, 2020).

Xenical warnings

Xenical shouldn’t be taken by people who (National Library, 2020):

  • Are pregnant

  • Have chronic malabsorption syndrome (inability to absorb nutrients from the intestine)

  • Have cholestasis (reduced or no flow of bile, the digestive fluid made by the liver)

  • Have anorexia or bulimia (Bansal, 2020)

If you’re breastfeeding, talk with your healthcare provider before taking Xenical. Small amounts of Xenical have been detected in the breast milk of one woman studied. However, it’s believed to be unlikely that harmful amounts of Xenical would be absorbed by your baby (Drugs and Lactation, 2021). Speak with your healthcare provider to determine whether you should take Xenical while breastfeeding.

Xenical drug interactions 

Xenical interacts with a number of other drugs. These interactions can have serious effects on your health. Be sure to tell your healthcare provider if you’re taking any of the medications listed below (National Library, 2020):

  • Cyclosporine

  • Levothyroxine

  • Warfarin

  • Amiodarone

  • Antiretroviral drugs (for HIV/AIDS)


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

How we reviewed this article

Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

November 17, 2021

Written by

Alison Dalton

Fact checked by

Steve Silvestro, MD

About the medical reviewer

Dr. Steve Silvestro is a board-certified pediatrician and Associate Director, Clinical Content & Education at Ro.

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