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

Alli is a branded product that contains the medication orlistat, which is used for weight loss. You can buy it from your pharmacy, although it is only suitable for overweight adults with a body mass index (BMI) of 28 kg/m2 or above who will commit to a reduced-calorie and lower-fat diet.

Exercise and other healthy living choices should also form an essential role in your weight loss plan. The medication can help those who are overweight to reduce their increased risk of developing a range of health problems such as diabetes, high blood pressure, heart disease, and even some cancers.

How do I take it?

Alli is available as capsules. You can take one capsule three times a day at breakfast, lunch, and dinner. You should take Alli 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 Alli. Make sure you swallow the capsules whole with a glass of water.

The medication orlistat found in Alli 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. It is best to take the multivitamin supplement in the evening before you go to bed so orlistat does not stop the fat-soluble vitamins from being absorbed into your body.

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

How does it work?

The active medication orlistat works by reducing the absorption of fat from your meals into your body. Orlistat inhibits enzymes in your digestive system called lipase that breaks down fat into smaller components that your digestive system is able to absorb. The fat you have not broken down can’t be absorbed and instead passes out of your body in your stools. Alli can prevent about a quarter of the fat from your meals from being absorbed from your digestive system.

Who should avoid the medication?

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

Speak with your doctor before taking Alli if you have kidney disease or take amiodarone, levothyroxine, or other medications for diabetes, epilepsy, high blood pressure, high cholesterol, or HIV. If you would usually check with your pharmacist or doctor before taking new medications, it may be best to speak to them first to ensure Alli is a safe option for you.

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, an urgency to have a bowel movement, and abdominal 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.

Remember that Alli isn’t a ‘magic bullet’ that will instantly get you to your ideal weight. It’s only part of a general weight loss program that includes a healthy calorie-controlled diet and regular exercise.

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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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