Skip to content


orlistat Alli Xenical

How It Works

Orlistat prevents your intestines from absorbing some of the fat from the food you eat. When taken 3 times a day with meals or within an hour of eating, orlistat blocks some of the fat you eat from being absorbed. Instead, this fat passes through your intestines and is excreted in your stool. When you absorb less fat, you take in fewer calories, which causes weight loss.

When a meal does not have any fat in it, you do not need to take orlistat.

Orlistat does not affect your appetite.

Why It Is Used

Orlistat is prescribed to help people who are obese (those with a body mass index [BMI] of 30 or higher) to lose weight. It may also be prescribed for people who have BMIs of 27 or higher when they have other conditions (such as diabetes, high blood pressure, or high cholesterol) that are made worse by being overweight.

Orlistat is also available in a lower strength without a prescription. This orlistat is meant for adults who are overweight (those who have a BMI of 25 or higher).

Orlistat is designed to be used along with a reduced-calorie diet, which is a diet that includes no more than 30% of its calories from fat. A regular exercise program is also an important part of any weight-loss treatment plan.

How Well It Works

Research reports that taking 120 mg of orlistat 3 times a day and following a reduced-calorie diet can result in greater weight loss after 6 months and 12 months, compared with taking a placebo.1

Side Effects

All medicines have side effects. But many people don't feel the side effects, or they are able to deal with them. Ask your pharmacist about the side effects of each medicine you take. Side effects are also listed in the information that comes with your medicine.

Here are some important things to think about:

  • Usually the benefits of the medicine are more important than any minor side effects.
  • Side effects may go away after you take the medicine for a while.
  • If side effects still bother you and you wonder if you should keep taking the medicine, call your doctor. He or she may be able to lower your dose or change your medicine. Do not suddenly quit taking your medicine unless your doctor tells you to.

Call or other emergency services right away if you have:

Call your doctor right away if you have:

Common side effects of this medicine include:

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Orlistat interferes with your body's absorption of fat-soluble vitamins. When you use orlistat, you will need to take a daily multivitamin supplement that contains vitamins A, D, E, and K and beta-carotene. Take the multivitamin once a day at least 2 hours before or after taking orlistat, such as at bedtime. Talk to your doctor or pharmacist about all the medicines you take, as there are risks combining some drugs and orlistat.

Taking medicine

Medicine is one of the many tools your doctor has to treat a health problem. Taking medicine as your doctor suggests will improve your health and may prevent future problems. If you don't take your medicines properly, you may be putting your health (and perhaps your life) at risk.

There are many reasons why people have trouble taking their medicine. But in most cases, there is something you can do. For suggestions on how to work around common problems, see the topic Taking Medicines as Prescribed.

Advice for women

If you are pregnant, breast-feeding, or planning to get pregnant, do not use any medicines unless your doctor tells you to. Some medicines can harm your baby. This includes prescription and over-the-counter medicines, vitamins, herbs, and supplements. And make sure that all your doctors know that you are pregnant, breast-feeding, or planning to get pregnant.


Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor if you are having problems. It's also a good idea to know your test results and keep a list of the medicines you take.

Complete the new medication information form (PDF) to help you understand this medication.


  1. DeLaet D, Schauer D (2011). Obesity in adults, search date September 2010. BMJ Clinical Evidence. Available online:

By Healthwise Staff See additional information
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Specialist Medical Reviewer Theresa O'Young, PharmD - Clinical Pharmacy
Current as of March 12, 2014

WebMD Medical Reference from Healthwise

Healthy Recipe Finder

Browse our collection of healthy, delicious recipes, from WebMD and Eating Well magazine.

Top searches: Chicken, Chocolate, Salad, Desserts, Soup

Heart Rate Calculator

Ensure you're exercising hard enough to get a good workout, but not strain your heart.

While you are exercising, you should count between...