Skip to main content

Orlistat capsules

Alli, Orlos, Xenical

Take one capsule three times daily with your main meals.

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 back passage (rectal) spotting, particularly at the beginning of treatment. These effects can be reduced by eating less fat in your meals.

Continue reading below

About orlistat

Type of medicine

An anti-obesity medicine

Used for

The treatment of obesity alongside a reduced-calorie diet

Also called

Xenical®; Alli®; Orlos®

Available as


Orlistat is a medicine that can help you to lose weight if you are obese or overweight. It works by interfering with the way fat is digested and absorbed by your body. It prevents the action of enzymes found in the digestive juices of your stomach and small intestine. These enzymes normally break down the fat which you consume in your diet, allowing it to be absorbed into your bloodstream. By blocking the enzymes' action, orlistat reduces the digestion of fat. This allows the fat you have eaten to be passed out of your body instead of being absorbed by your body, and this helps you to lose weight.

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

Orlistat is available on prescription, and lower-strength capsules (Alli® brand) can also be bought from pharmacies. It is not suitable for everyone and a number of guidelines apply as to who can be supplied with orlistat - more information about this can be found in the separate health information leaflet called Orlistat Weight Loss Medicine.

Before taking orlistat

Some medicines are not suitable for people with certain conditions, and sometimes a medicine may only be used if extra care is taken. For these reasons, before you start taking orlistat it is important that your doctor or pharmacist knows:

  • If you are pregnant, trying for a baby or breastfeeding.

  • If you have any problems with the way your kidneys work.

  • If you have a condition called chronic malabsorption syndrome, where your food is not absorbed properly.

  • If you have a problem with the flow of bile to your liver, a condition called cholestasis.

  • If you have ever had an allergic reaction to a medicine.

  • If you are taking any other medicines. This includes any medicines you are taking which are available to buy without a prescription, as well as herbal and complementary medicines.

Continue reading below

How to take orlistat

  • Before you start the treatment, read the manufacturer's printed information leaflet from inside the pack. It will give you more information about orlistat and will provide you with a full list of the side-effects which you may experience from taking it.

  • Take orlistat exactly as your doctor or pharmacist tells you to. There are two strengths of capsules - 60 mg and 120 mg. The lower-strength capsule is available from pharmacies whilst the higher-strength capsule is only available on a prescription from a doctor.

  • The usual dose of orlistat is one capsule (60 mg or 120 mg) taken with each of your three main meals of the day. Swallow the capsule with a drink of water as you are about to eat the meal or soon afterwards. It can be taken up to one hour after a meal. Do not take more than three doses a day.

  • Orlistat only works when there are fats in what you eat, so if you miss a meal or if you eat a meal which is fat-free then do not take a dose of orlistat.

  • If you forget to take a dose, do not worry; just take a capsule with your next meal as usual. Do not take two doses together to make up for a forgotten dose.

Getting the most from your treatment

  • 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.

  • To lose weight, the best chance of long-term success is to eat a well-balanced, calorie-controlled diet that is low in fat and rich in fruit and vegetables. If you are able, you should also exercise regularly. See the separate health information leaflet called Weight Loss (Weight Reduction) for more details. Your practice nurse will be able to give you further help and advice about eating a healthy diet and taking suitable exercise.

  • If you have bought orlistat from a pharmacy, 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 within three months from starting orlistat; if not, the treatment should be stopped. Do not continue taking orlistat for longer than six months without seeing a doctor.

  • If you have been prescribed orlistat, your doctor will want to review your weight and treatment regularly to decide if it is still appropriate for you to carry on taking orlistat. You must lose at least 5% of your weight within three months from starting orlistat; if not, the treatment is likely to be stopped. It may also be necessary for you to have some blood tests during treatment to check your blood lipids. If you continue to lose weight after six months, your doctor may advise that you continue to take orlistat for up to a year, or possibly longer.

  • 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. Reducing the amount of fat you eat in your meals will reduce the likelihood of these harmless, but unpleasant, side-effects.

  • Orlistat can interfere with the absorption of various medicines, including possibly the contraceptive pill. If you take 'the pill' and you have severe diarrhoea as a side-effect of taking orlistat, it could reduce the effectiveness of the contraception. If you experience diarrhoea, use another method of contraception in addition to the pill - for example, a condom.

  • Orlistat can also interfere with the absorption of vitamins which are fat-soluble. These are vitamins A, D, E and K. If you decide to take a multivitamin supplement, take it at a time when you are not also taking orlistat. The best time to take the supplement would be at bedtime.

  • If you have diabetes, it is important that you speak with a doctor before you start taking orlistat, as it can affect the control of your diabetes. This may require extra monitoring.

  • After you stop taking orlistat, you may put some weight back on. Remembering to continue with your healthy eating and increased level of physical activity can help to prevent this.

Continue reading below

Can orlistat cause problems?

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains some of the most common ones associated with orlistat. You will find a full list in the manufacturer's information leaflet supplied with your medicine. The unwanted effects often improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following continue or become troublesome.

Very common orlistat side-effects (these affect more than 1 in 10 people)

What can I do if I experience this?

Lower tummy (abdominal) discomfort, oily spotting from your back passage, wind, loose oily stools, an urgent need to open your bowels, pain around your back passage

These symptoms generally occur at the start of treatment as your body is adjusting. Reducing the fat content in your meals will help


Drink plenty of water and ask a pharmacist to recommend a suitable painkiller. If the headaches continue, let your doctor know

Throat and chest infections, flu-like symptoms

If troublesome, speak with your doctor or pharmacist for advice

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 the capsules, speak with your doctor or pharmacist for further advice.

How to store orlistat

  • Keep all medicines out of the reach and sight of children.

  • Store in a cool, dry place, away from direct heat and light.

Important information about all medicines

Important information about all medicines

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 you or someone else might have taken an overdose of this medicine, go to the accident and emergency department of your local hospital. 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.

Do not 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.

Report side effects to a medicine or vaccine

If you experience side effects, you can report them online through the Yellow Card website.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

symptom checker

Feeling unwell?

Assess your symptoms online for free