BMA Concise Guide to Medicine & Drugs


Brand names Alli, Xenical

Used in the following combined preparations None


Drug group Anti-obesity drug

Overdose danger rating Low

Dependence rating Low

Prescription needed No

Available as generic No


Orlistat blocks the action of stomach and pancreatic enzymes (lipases) that digest fats; hence less dietary fat is absorbed and more passes out in the faeces. This leads to reduced calorie uptake and helps to produce weight loss as the body burns stored fat to provide energy. The effectiveness of orlistat varies from person to person, and it should only be used to lose weight in conjunction with healthy lifestyle measures. Because of how orlistat works, the faeces become oily, and this can cause flatulence. Part of the drug’s effect may be due to people reducing their fat intake to avoid these side effects. As fat absorption is reduced, there is a danger of fat-soluble vitamins being lost to the body, and a multivitamin supplement may be needed to compensate (see Diet advice).


Follow instructions on the label. Call your doctor if symptoms worsen.

How taken/used Capsules.

Frequency and timing of doses Just before, during, or up to 1 hour after each main meal (up to 3 x daily). If a meal is omitted or contains no fat, do not take the dose of orlistat.

Adult dosage range 120–360mg daily.

Onset of effect 30 minutes; excretion of excess faecal fat begins about 24–48 hours after the first dose.

Duration of action Orlistat is not absorbed from the gut, and potentially continues to work as it passes through the intestines. If you stop taking the drug, faecal fat returns to normal in 48–72 hours.

Diet advice Eat a nutritionally balanced diet that does not contain quite enough calories, and that provides about 30 per cent of the calories as fat. Eat lots of fruit and vegetables. The intake of fat, carbohydrate, and protein should be distributed over the three main meals. If a multivitamin supplement is needed, it should be taken at least 2 hours before an orlistat dose or at bedtime.

Storage Keep in original container at room temperature out of the reach of children.

Missed dose No cause for concern. Take the next dose with the next meal.

Stopping the drug The drug can be safely stopped as soon as it is no longer needed.

Exceeding the dose An occasional unintentional extra dose is unlikely to be a cause for concern. But if you notice any unusual symptoms, or if a large overdose has been taken, notify your doctor.


Most side effects of orlistat depend on how much fat is eaten, as well as the dose of the drug. Common side effects include liquid, oily stools, faecal urgency, flatulence, abdominal or rectal pain, headache, menstrual irregularities, anxiety, fatigue, nausea, infections (e.g. respiratory infections), and hypoglycaemia (low blood sugar). Discuss with your doctor if these are severe.


General note Orlistat reduces absorption of fat-soluble vitamins (A, D, E, and K) so that a multivitamin supplement may be needed. This is particularly important in growing teenagers.

Ciclosporin, oral anticoagulants, amiodarone, and anti-epileptics Orlistat may reduce the effects of these drugs.

Acarbose Avoid using orlistat if taking acarbose.


Be sure to consult your doctor or pharmacist before taking this drug if:

· You have diabetes.

· You have chronic malabsorption syndrome.

· You have gallbladder or liver problems.

· You are taking lipid-lowering drugs.

· You are taking other medicines.

Pregnancy Safety not established. Discuss with your doctor.

Breast-feeding Safety not established. Discuss with your doctor.

Infants and children Should not be used in under-18s except on specialist advice.

Over 60 No special problems.

Driving and hazardous work No special problems.

Alcohol No special problems.


Orlistat treatment should be stopped after 12 weeks if you have not lost 5 per cent of your body weight since the start of treatment. It should also be stopped if you have lost less than 10 per cent of your body weight over the first 6 months. If you have, then the drug may be continued, for up to a maximum of 2 years, until your target weight is approached.

When orlistat treatment is stopped, there may be gradual weight gain.