Orlistat, which is a type of medicine called a lipase inhibitor, was first launched as Xenical. Orlistat is prescribed to aid weight loss in 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.
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.
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.
We would recommend you take a supplement of Vitamins A,D,E and K whilst taking orlistat.
Medicines and their possible side effects can affect individual people in different ways. 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 orlistat and do not take it with meals that are high in fat.
The following are some of the side effects that are known to be associated with orlistat:
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.
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 orlistat, please read the information provided with the medicine or consult your doctor or pharmacist.
It is important to follow a reduced fat, lower calorie diet while you are taking orlistat.
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.
Orlistat 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 persistent rectal bleeding while taking orlistat you should consult your doctor so that this can be investigated.
Orlistat 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, e.g. condoms, if you experience severe diarrhoea while taking this medicine.
If you have been unable to lose at least five per cent of your body weight after 12 weeks of treatment with orlistat you should stop taking it and consult a doctor.
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.
Orlistat should be used with caution in:
- People with long-term kidney disease.
- People with an underactive thyroid gland (hypothyroidism). (Orlistat may affect the absorption of levothyroxine).
- Epilepsy. (Orlistat may affect the absorption of antiepileptic medicines).
- People taking antiretrovirals for HIV infection. (Orlistat may affect the absorption of these medicines.)
- People who are also taking amiodarone, an anticoagulant such as warfarin, an antidepressant or an antipsychotic medicine. (Orlistat may make these medicines less effective).
Orlistat should NOT 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.
Orlistat 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 orlistat and inform your doctor or pharmacist immediately.
The patient information leaflet (PIL) is a leaflet containing specific information about medical conditions, doses and side effects. You can download a copy of the PIL here:
Patient Info Leaflet