• While you are taking orlistat you should eat a well-balanced, calorie-controlled diet that is rich in fruit and vegetables and contains an average of a third of the calories from fat.
  • If there is no fat in one of your meals or if you miss a meal, there is no need for you to take a dose of orlistat.
  • Common side-effects include wind, loose stools and rectal spotting, particularly at the beginning of treatment. These effects can be reduced by eating less fat in your meals.
  • Orlistat is not suitable for under 18 year-olds.
Type of medicine Anti-obesity medicine
Used for Treatment of obesity (along with a reduced-calorie diet)
Also called Xenical®
Available as Capsules and chewable tablets

Orlistat is used in the treatment of obesity alongside a low-calorie diet to help you lose weight. It works by interfering with the way that fat is digested and absorbed into your body. It works on your stomach and small intestine where it prevents the action of two enzymes found in digestive juices. These enzymes normally break down the fats which you consume in your diet. The fat that orlistat blocks from being digested, is passed out with your stools instead of being absorbed into your body.

Orlistat only prevents about a third of the fat you eat from being absorbed so it is also important for you to eat a weight-reducing diet and exercise regularly.

Before taking orlistat make sure your doctor or pharmacist knows:

  • If you are pregnant, trying for a baby or breast-feeding.
  • If you have kidney problems.
  • If you have chronic malabsorption syndrome (where your food is not absorbed properly).
  • If you have cholestasis (a problem with the flow of your bile).
  • If you have ever had an allergic reaction to this or to any other medicine.
  • If you are taking other medicines, including those available to buy without a prescription, herbal and complementary medicines.
  • Before taking orlistat, read the manufacturer's printed information leaflet from inside the pack.
  • Take orlistat exactly as your doctor or pharmacist has told you. There are two strengths of capsules and one strength of tablets. The higher-strength capsule is only available on a prescription from a doctor.
  • Take one capsule or tablet just before or up to one hour after each of your main meals. Do not take more than three doses each day. If you are taking capsules, swallow each dose with a little water. If you are taking tablets, chew them before swallowing.
  • If you miss a meal or eat a meal which does not contain fat, then there is no need for you to take that dose of orlistat.
  • If you forget to take a dose, do not worry, just take a dose with your next meal as normal. Do not take two doses together to make up for a forgotten dose.
  • To lose weight, the best chance of long-term success is to eat a healthy diet and, if you are able, to exercise regularly. See separate leaflet called 'Weight Reduction - How to Lose Weight' for more details. Your practice nurse will also be able to give you further help and advice about a healthy diet and exercise.
  • While you are taking orlistat you should eat a well-balanced, calorie-controlled diet that is rich in fruit and vegetables and contains an average of a third of the calories from fat.
  • Orlistat is only suitable if your body mass index (BMI) is 28 kg/m2 or greater. BMI is calculated by dividing your weight in kilograms by the square of your height in metres. So, for example, if you weigh 85 kg and are 1.7 metres tall, your BMI is 85/(1.7 x 1.7), which is 29. Alternatively, your practice nurse can measure and weigh you, and tell you your BMI.
  • The fat which remains undigested from your diet can cause changes in your bowel habit, resulting in wind, loose stools, and oily spotting from your back passage. By reducing the amount of fat you eat in your meals, you can reduce the likelihood of experiencing these harmless but unpleasant side-effects.
  • Check your weight regularly and, if you have not lost weight after three months, see your doctor or pharmacist for further advice. You must lose at least 5% of your weight by three months from starting orlistat, and at least 10% of your weight by six months.
  • Since orlistat may interfere with the absorption of vitamins A, D, E and K, you may wish to take a multivitamin supplement. Take this at a time when you are not taking orlistat, such as at bedtime or at least two hours after you have taken your orlistat dose.
  • If you take the contraceptive pill and have severe diarrhoea, you should use other methods of contraception in addition to the pill - for example, condoms. This is because having diarrhoea may prevent oral contraceptives from working fully.
  • If you are diabetic, speak to a doctor before taking orlistat, as it may affect the control of your diabetes, requiring a change in your treatment.
  • Usually orlistat is taken for up to six months, but this may be longer if your treatment is prescribed by a doctor.
  • Remember to continue your healthy eating and increased level of physical activity even after you have finished taking orlistat.

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. These usually improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following side-effects continue or become troublesome.

Common orlistat side-effects - these affect around 1 in 10 people who take this medicine What can I do if I experience this?
Headache Ask your pharmacist to recommend a suitable painkiller
Abdominal discomfort, oily spotting from your back passage, wind, loose stools, an urgent need to open your bowels, pain around your back passage These symptoms are generally mild and occur at the start of treatment as your body is adjusting. Reducing the fat content in your meals will help
Tooth and gum problems See your dentist if you are concerned
Anxiety, tiredness, menstrual cycle irregularities Speak with your doctor or pharmacist if any of these become troublesome

Important: if you experience any bleeding from your back passage, speak with your doctor for advice.

If you experience any other symptoms which you think may be due to this medicine, discuss them with your doctor or pharmacist.

  • Keep all medicines out of the reach and sight of children.
  • Store in a cool, dry place, away from direct heat and light.
  • If you buy any medicines check with a pharmacist that they are safe to take with your other medicines
  • Never take more than the prescribed dose. If you suspect that someone has taken an overdose of this medicine go to the accident and emergency department of your local hospital at once. Take the container with you, even if it is empty.
  • If you are having an operation or dental treatment, tell the person carrying out the treatment which medicines you are taking.
  • This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.
  • Never keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.
  • If you have any questions about this medicine ask your pharmacist.

Further reading & references

  • British National Formulary; 62nd Edition (Sep 2011) British Medical Association and Royal Pharmaceutical Society of Great Britain, London
  • Manufacturer's PIL, Xenical® 120 mg hard capsules; Manufacturer's PIL, Xenical® 120 mg hard capsules, Roche Products Limited, electronic Medicines Compendium. Dated April 2011.

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Helen Allen
Current Version:
Peer Reviewer:
Dr Adrian Bonsall
Last Checked:
Document ID:
1437 (v28)
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