Orlistat for obesity


Generic Name Brand Name
orlistat Xenical

How It Works

Orlistat prevents your intestines from absorbing some of the fat from the food you eat. When taken 3 times per day with meals, orlistat blocks about one-third 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.

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 with BMIs of 27 or higher when they have other conditions (such as diabetes or sleep apnea) that are made worse by being overweight.

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

One study showed that:1

  • About 30% of people who took orlistat for 12 to 18 months lost 10% or more of their weight. In the placebo group, 24% had lost this amount of weight at 12 months and 16% at 18 months.
  • About 60% of people who took orlistat for 12 to 18 months lost 5% or more of their weight. In the placebo group, 46% had lost this amount of weight at 12 months and 37% at 18 months.

Research reports that taking 120 mg of orlistat 3 times per day and following a reduced-calorie diet can result in greater weight loss after 6 months and 12 months, compared with taking a placebo.2

Another study found that people taking orlistat lost an average of 6.4 lb (2.9 kg) more by 12 months compared to those who took a placebo.3

Side Effects

The side effects of orlistat are all related to your intestines or bowels. Only very small amounts of orlistat are absorbed into the bloodstream, so it has little effect on other body systems.

Changes in bowel habits include:

  • Oily spotting, flatulence (with discharge), and an urgent need to go to the bathroom. This was reported by 22% to 27% of people who used orlistat.2
  • Gas with bowel movements.
  • Oily or fatty stool. The oil seen in a bowel movement may be clear, orange, or brown.
  • An increased number of bowel movements.
  • Inability to control bowel movements.

Some people have these side effects only in the first few weeks of use. Most people have fewer side effects after 1 year of use. Others have them as long as they take orlistat. Most people find these side effects unacceptable if they do not go away in a few weeks. Inability to tolerate these side effects is the most common reason people stop using this medicine.

The side effects increase when you eat more fat and decrease when you eat less fat. People using orlistat are advised to eat foods with no more than 30% fat. This amount of fat keeps the side effects in a range that most people can manage.

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

What To Think About

Xenical is approved for the management of obesity in adolescents 12 to 16 years of age.

Orlistat interferes with your body's absorption of fat-soluble vitamins. When you use orlistat, you should 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.

Because orlistat blocks fat absorption, some people believe they can eat more fat without weight gain. But the unpleasant side effects of orlistat increase with the amount of fat a person eats. Research shows that people taking orlistat may want to eat less fat than before, in order to reduce these side effects. As long as you do not replace the fat calories in your diet with calories from other foods, orlistat will work as intended.

Ask your doctor if there is a support program that helps you with lifestyle changes along with this medicine.

Treatment with orlistat may lower the level of total cholesterol and triglycerides (fats) in the blood and thus lower your risk of heart disease. It may also have a positive effect on levels of blood sugar and insulin, which may lower your risk of developing type 2 diabetes.

Complete the new medication information form (PDF)(What is a PDF document?) to help you understand this medication.



  1. Krempf M, et al. (2002). Weight reduction and long-term maintenance after 18 months' treatment with orlistat for obesity. International Journal of Obesity, 27(5): 591–597.
  2. Arterburn DE, et al. (2008). Obesity in adults, search date February 2007. Online version of BMJ Clinical Evidence: http://www.clinicalevience.com.
  3. Li Z, et al. (2005). Meta-analysis: Pharmacologic treatment of obesity. Annals of Internal Medicine, 142(7): 532–546.

Last Updated: April 16, 2009

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