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Dr Karen Martin
Reviewed by Dr Karen MartinReviewed on 19.10.2023 | 3 minutes read

Orlistat is a medication used for weight loss. You can buy it from your pharmacy under the brand name Alli. It is only suitable for overweight adults with a BMI of 28 kg/m2 or above who will commit to a reduced-calorie and lower-fat diet. Exercise should also form an essential role in the weight loss plan.

Weight loss is crucial if you are overweight, as excess weight puts you at an increased risk of developing a range of health problems such as diabetes, high blood pressure, heart disease, and even some cancers. There is also a higher-strength version of orlistat that is only available on prescription.

How do I use the medication?

Orlistat is available as capsules. You can take one capsule three times a day at breakfast, lunch, and dinner. You should take orlistat just before, during, or up to one hour after meals. If you miss a meal or your meal does not contain any fat, you should not take orlistat. Make sure you swallow the capsules whole with a glass of water.

Orlistat can decrease the absorption of fat-soluble vitamins (namely vitamins A, D, E, and K). Therefore, you should take a multivitamin supplement containing these vitamins. Taking the multivitamin supplement in the evening before you go to bed is best, so orlistat does not stop the fat-soluble vitamins from being absorbed into your body.

Do not take orlistat for longer than six months without consulting your doctor. If you have not lost weight (at least a 5% reduction) after taking orlistat for 12 weeks, you should speak with your doctor or pharmacist, as they may not want you to continue treatment.

How does the medication work?

Orlistat works by reducing fat absorption from your meals into your body. Orlistat inhibits enzymes in your digestive system called lipases that break down fat into components (called fatty acids and monoglycerides) which your digestive system then absorbs. The fat you have not broken down can’t be absorbed and instead passes out of your body in your stools. Orlistat can prevent about a quarter of the fat from your meals from being absorbed by your digestive system.

Should anyone avoid taking it?

Do not take orlistat if you are allergic to it or another ingredient listed in the medicine. It is not suitable for anyone under 18 or with a BMI lower than 28 kg/m2. Do not take it if you are pregnant or breastfeeding, have problems absorbing food, have the medical condition cholestasis, take cyclosporin, or take warfarin or another blood-thinning medication.

Speak with your doctor before taking orlistat if you have:

  • kidney disease
  • diabetes
  • a thyroid condition
  • epilepsy
  • HIV.

If you take any prescription, over-the-counter or herbal medicines, ask your doctor or pharmacist to check if they are safe to take alongside orlistat.

Are there any side effects?

As with all medications, some people may experience side effects. Some common ones include flatulence, fatty or oily stools, oily spotting on your underwear, sudden bowel movements, and stomach pain. Eating lower-fat meals can help to reduce side effects. You should speak with your doctor or pharmacist if you are concerned about any side effects.

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This article has been written by UK-based doctors and pharmacists, so some advice may not apply to US users and some suggested treatments may not be available. For more information, please see our T&Cs.
Dr Karen Martin
Reviewed by Dr Karen Martin
Reviewed on 19.10.2023
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