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How does it work?
Xenical capsules contain the active ingredient orlistat, which is a type of medicine called a lipase inhibitor. It is used to aid weight loss in people who are overweight or obese. Orlistat is also available without a brand name, ie as the generic medicine.
Orlistat is not absorbed into the bloodstream, but works locally in the stomach and small intestine, where it prevents the action of two compounds found in the digestive juices. These compounds (known as enzymes) are called gastric and pancreatic lipases. They normally break down fats that we consume in our diet.
The fats we consume in our diets are made of molecules that are too large to be absorbed from the gut into the bloodstream. They need to be broken down into smaller molecules during the process of digestion, in order to be absorbed. Gastric and pancreatic lipases are the compounds in the gut that carry out this function.
Orlistat works by preventing the gastric and pancreatic lipases from working. The medicine is taken at mealtimes to prevent fat that is eaten in the meals from being broken down and absorbed by the body. This means the body cannot use the fat as a source of energy, or convert it into fat tissue. Instead, the fat is excreted in the faeces. This helps weight loss.
Orlistat should be used with increased exercise and a reduced calorie, lower fat diet. Approximately 30 per cent of your daily calories should come from fat, and your daily intake of fat, carbohydrate and protein should be spread evenly over your three main meals. For example, for a diet of 1400 calories per day, each meal should contain approximately 15 grams of fat.
The actual calorie intake and fat consumption that you should follow will depend on your initial weight and level of physical activity - there is guidance provided in the package leaflet, and your doctor or pharmacist can also advise.
What is it used for?
Orlistat is prescribed to aid weight loss in obese people who have a body mass index (BMI) of 30kg/m² or more. It can also be prescribed to overweight people who have a BMI of 28kg/m² or more, if they also have additional risk factors for obesity-related diseases.
How do I take it?
- One capsule should be taken immediately before, during, or up to one hour after each main meal. If a meal is missed, or contains no fat, you should leave out the dose. This is because the medicine will have no effect if no fat has been consumed.
- Each capsule should be swallowed whole with a drink of water.
- Do not take more than three capsules per day. Higher doses have been shown to be no more effective.
- It is important to follow a reduced fat, lower calorie diet while you are taking this medicine. If you take orlistat with a meal that is very high in fat you are more likely to experience digestive side effects such as wind, oily spotting from the rectum, sudden bowel motions, and soft, fatty or oily stools.
- This medicine may potentially reduce the absorption of fat-soluble vitamins (A,D,E,K) from the gut. To make sure you are still getting adequate nutrition your diet should be rich in fruit and vegetables. Your doctor may also recommend a multivitamin supplement. If you do take a multivitamin supplement, it should be taken at least 2 hours after your orlistat dose, or at bedtime.
- If you experience any severe or persistant rectal bleeding while taking this medicine you should consult your doctor so that this can be investigated.
- This medicine can cause diarrhoea, which if severe, can reduce the effectiveness of oral contraceptive pills. If you are taking the pill for contraception you may need to use an additional method of contraception to prevent pregnancy, eg condoms, if you experience severe diarrhoea while taking this medicine. Follow the instructions in the leaflet provided with your pill, or in our factsheet on your pill (follow the link above to find your pill).
- Your doctor may ask you to stop treatment if you have been unable to lose at least five per cent of your body weight after 12 weeks of treatment with this medicine.
- Once you stop taking this medicine it is important to continue to follow a healthy, balanced diet and take regular exercise to make sure the weight you have lost stays off.
Use with caution in
- People with long-term kidney disease.
- People with an underactive thyroid gland (hypothyroidism). (Orlistat may affect the absorption of levothyroxine - see end of this factsheet for more information.)
- Epilepsy. (Orlistat may affect the absorption of antiepileptic medicines - see end of this factsheet for more information.)
- People taking antiretrovirals for HIV infection. (Orlistat may affect the absorption of these medicines - see end of this factsheet for more information.)
- People who are also taking amiodarone, an anticoagulant such as warfarin, an antidepressant or an antipsychotic medicine. (Orlistat may may make these medicines less effective - see end of this factsheet for more information).
Not to be used in
- People who suffer from a long-term condition in which the gut does not absorb sufficient nutrients (chronic malabsorption syndrome).
- People in whom the normal flow of bile from the liver to the intestines is blocked (cholestasis).
- Women who are breastfeeding.
- This medicine is not licensed for use in children under 18 years of age. However, it may sometimes be prescribed by specialists for children over 12 years of age who are obese. This is an unlicensed use of the medicine.
This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.
If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.
Pregnancy and breastfeeding
Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.
- The safety of this medicine in pregnancy has not been established. It should be used with caution during pregnancy and only if the benefits outweigh any possible risks to the developing baby. Ask your doctor for advice if you think you could be pregnant while taking this medicine.
- It is not known if this medicine passes into breast milk. It should not be taken by mothers who are breastfeeding. Seek further medical advice from your doctor.
Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Just because a side effect is stated here does not mean that all people using this medicine will experience that or any side effect.
You are less likely to experience digestive side effects if you follow the instructions on what to eat while taking this medicine and do not take it with meals that are high in fat.
Very common (affect more than 1 in 10 people)
- Oily spotting from the rectum.
- Abdominal pain or discomfort.
- Flatulence (wind), sometimes with discharge.
- Oily or fatty stools.
- Urgent or increased need to open the bowels.
- Low blood sugar levels (hypoglycaemia) in people with type 2 diabetes.
- Upper airway infections such as flu.
Common (affect between 1 in 10 and 1 in 100 people)
- Pain or discomfort in the rectum.
- Abdominal bloating in people with type 2 diabetes.
- Faecal incontinence.
- Tooth or gum disorders.
- Chest infections.
- Urinary tract infections.
- Irregular menstrual periods.
Unknown frequency (reported since the medicine has been on the market)
The side effects listed above may not include all of the side effects reported by the medicine's manufacturer.
For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.
How can this medicine affect other medicines?
It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while taking this one, to make sure that the combination is safe.
The manufacturer of this medicine recommends that orlistat should not be used in combination with the following medicines:
- acarbose (as this combination has not been studied)
- ciclosporin (as orlistat may decrease the blood level of ciclosporin and make it less effective).
If it is unavoidable to use orlistat in combination with ciclosporin, the level of ciclosporin in your blood should be monitored more frequently. In particular, your ciclosporin level should be checked after you start and stop taking orlistat.
If you are taking the anticoagulant medicines warfarin, acenocoumarol or phenindione in combination with orlistat, your blood clotting time (INR) should be monitored more frequently, particularly after you start and stop taking orlistat.
Orlistat may decrease the blood level of amiodarone, a medicine for irregular heartbeats. Your doctor may want to monitor your heart more closely if you are taking amiodarone in combination with this medicine.
This medicine may possibly reduce the absorption of levothyroxine (taken for an underactive thyroid gland) from the gut. If you have an underactive thyroid gland you should let your doctor know if you think your thyroxine has become less effective after starting treatment with this medicine.
This medicine may possibly reduce the absorption of antiepileptic medicines such as valproate or lamotrigine from the gut. If you are taking antiepileptic medicines you should let your doctor know if your seizures have got worse or become more frequent after starting treatment with this medicine.
This medicine may possibly reduce the absorption of medicines used to treat HIV infection such as efavirenz or lopinavir from the gut, which could potentially make these medicines less effective.
If you take a multivitamin supplement with this medicine, it should be taken at least two hours after your orlistat dose, or at bedtime, as otherwise the orlistat will prevent the vitamins being absorbed.
If you are taking medicines for diabetes, you may need an adjustment in your dose if you lose weight while taking this medicine. This is because weight loss may be accompanied by an improvement in your blood sugar levels. Ask your doctor or pharmacist for advice.
If you are taking medicines for high blood pressure or medicines for high cholesterol levels, you may need an adjustment in your dose if you lose weight while taking this medicine. This is because your weight loss may be accompanied by an improvement in your blood pressure or cholesterol levels. Ask your doctor or pharmacist for advice.
This medicine can cause diarrhoea, which if severe, can reduce the absorption of oral contraceptive pills from the gut and thus make them less effective at preventing pregnancy. If you are taking the pill for contraception you may need to use an additional method of contraception, eg condoms, to prevent pregnancy, if you experience severe diarrhoea while taking this medicine. Follow the instructions in the leaflet provided with your pill, or in our factsheet on your pill.
If you are taking an antidepressant or antipsychotic medicine, including lithium, it is important to tell your doctor if you think your medicine has become less effective after you start taking orlistat. This has been reported in a few people taking orlistat with an antidepressant or antipsychotic medicine.
Other medicines containing the same active ingredient
Orlistat capsules are also available without a brand name, ie as the generic medicine.