Orlistat is a medicine which can help you to lose weight if you are obese or overweight. It works by interfering with the way that fat is digested and absorbed into the body. Doctors have guidelines as to when orlistat can be prescribed. You can also buy orlistat from pharmacies - but certain conditions apply, detailed below. If you take orlistat, as it may possibly interfere with the absorption of some vitamins, you should take a multivitamin supplement at bedtime. Tell your doctor or pharmacist if you take any other medicines, as orlistat can interfere with the absorption of some medicines.


Orlistat is a medicine which can help you to lose weight if you are obese or overweight. It works by blocking chemicals (enzymes) in your gut which digest fat. Nearly a third of the fat that you eat is blocked by orlistat. The undigested fat is not absorbed into your body, and is passed out with your stools (faeces). The normal dose is one capsule - 120 mg, three times a day with each meal. However, you do not need to take one if there is no fat in the meal or if you miss a meal.

Orlistat is the only medicine available to prescribe to help with weight loss. Two other medicines - sibutramine and rimonabant - previously used to help with weight loss are no longer available in the UK because of concerns over their safety.



You are obese or overweight if you are carrying excess body fat. As an adult, one way you can find out whether you are overweight or obese, and whether your health may be at risk, is by calculating your body mass index (BMI).

BMI is used to estimate how much of your body is made up of fat, and if someone's weight is putting their health at risk. It is a measure of your weight related to your height. BMI may not be an accurate measure for people who are very muscular, because muscle weighs more than fat. In those people, a high BMI may not necessarily mean they have too much fat in their body.

Your doctor will normally calculate your BMI and use this number, as well as other factors, to decide if you should be prescribed orlistat.


Calculating your BMI

Your BMI is calculated by dividing your weight (in kilograms) by the square of your height (in metres). So, for example:

  • If you weigh 70 kg and are 1.55 metres tall, your BMI is 70/(1.55 x 1.55), which is 29.
  • If you weigh 85 kg and are 1.7 metres tall, your BMI is 85/(1.70 x 1.70), which is 29.

If you do not have scales, your practice nurse can measure and weigh you, and tell you your BMI. You can also use our calculator to find out your BMI.

Normal healthy BMI is 18.5 to 24.9 kg/m2. In general, the more your BMI is over 25, the more overweight or obese you are, and the greater the risk to your health. If you are very overweight, the risks to your health may be very high.

Another way to find out if you are overweight or obese is to measure your waist circumference. This is discussed in detail in a separate leaflet called Obesity and Overweight in Adults.


To lose weight, the best chance of long-term success is to eat a healthy diet and, if you are able, to exercise regularly. To lose weight, you need to be using more energy (calories) than you are taking in by eating.

There is only a limited role for medicines to help with weight loss. Orlistat is a medicine that is sometimes advised. However, it is no 'wonder drug'; it only partially helps, and you still need to make lifestyle changes to improve your diet, eat less and increase your physical activity levels to lose weight.

For more information see separate leaflet called Weight Reduction - How to Lose Weight.


Studies have shown that, on average, orlistat, plus a weight-reducing diet and exercise, causes more weight loss than a weight-reducing diet and exercise alone. Some people lose 10% or more of their body weight within six months with the help of orlistat. In others, it is less effective.

One reason why orlistat may not work is that you may think that you can relax your weight-reducing diet, and the orlistat will 'do it all'. This is not true. In order to lose weight you still have to eat less, and exercise regularly. Remember, orlistat prevents only some of the fat that you eat from being absorbed (just under a third). But, if you do not keep to a healthy weight-reducing diet, and you eat more fat (chocolates, cakes, etc), the extra fat that you eat will easily cancel out the effect of the orlistat.


Orlistat is not used in everyone who wants to lose weight. It is only recommended in people over a certain BMI. For a doctor to prescribe orlistat, they also need to be sure that you have tried changing your diet and increasing your physical activity levels first.

Doctors are expected to use the following guidelines when prescribing orlistat:

  • Your BMI:
    • Must be 30 or above; or
    • Must be 28 or above, and you have a medical condition that would benefit from losing weight (such as diabetes or high blood pressure).
  • You must lose at least 5% of your weight by three months from starting orlistat; if not, treatment should be stopped.


If you have lost 5% of your weight within three months, there is no restriction on how long orlistat may be prescribed. However, most doctors will review treatment regularly, and will decide if it is still appropriate for you to carry on taking orlistat. If you continue to lose weight after six months, your doctor may advise that you continue to take orlistat. This may be for up to 1-2 years, or longer if you have a great deal of weight to lose.


After treatment is stopped, a number of people who have lost weight with the help of orlistat put weight back on. Try to anticipate this. Once you have lost some weight, you are more likely to keep your weight down if you stick to a healthy diet, exercise regularly (if you are able), and weigh yourself once a week.


Orlistat is available on prescription from your doctor (120 mg) and low-dose orlistat (60 mg) is also available to buy over-the-counter in pharmacies. Pharmacists cannot just sell it to anyone. They are also expected to follow guidelines which include:

  • Your BMI must be 28 or above.
  • Your BMI should be checked on each occasion that you request orlistat.
  • You must be over the age of 18.
  • You should not take orlistat for more than six months over the counter.
  • If you have not lost weight after taking orlistat for three months, you should not continue to take it.

Your pharmacist will also give you advice on an appropriate diet - a low-calorie and low-fat diet.


The main side-effects are caused by the fat which is passed out with your stools (faeces). You may get fatty smelly stools, urgency to get to the toilet, oily spotting on your underclothes, and excess wind. These side-effects are less likely if you eat a low-fat diet. They tend to settle with time, possibly because if they occur they remind you that you should be eating a low-fat diet. Other side-effects are rare. Note: the above is not the full list of side-effects for those taking orlistat. Please see the leaflet that comes with your medicine for a full list of possible side-effects and cautions.


The following people should not take orlistat:

  • Pregnant or breast-feeding women.
  • People under the age of 18.
  • People who have a condition where food is not absorbed properly (a malabsorption syndrome).
  • People with cholestasis. This is a condition where bile does not flow properly from the liver to the duodenum.

Orlistat can also interfere with the absorption of various medicines and vitamins and affect the way that they work. For example, orlistat interferes with:

It may also affect how well contraceptive pills work if you get so much diarrhoea that they don't absorb properly. If you take orlistat:

  • 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.
  • Tell your doctor or pharmacist about other medicines that you take, before starting on orlistat.
  • Take a multivitamin supplement at bedtime - a time when you will not be taking orlistat - to help ensure adequate vitamin intake.

Always read the packet leaflet for a full list of cautions and of people who should not take orlistat.


If you think you have had a side-effect to one of your medicines, you can report this on the Yellow Card Scheme. You can do this online at the following web address: www.mhra.gov.uk/yellowcard.

The Yellow Card Scheme is used to make pharmacists, doctors and nurses aware of any new side-effects that your medicines or any other healthcare products may have caused. If you wish to report a side-effect, you will need to provide basic information about:

  • The side-effect.
  • The name of the medicine which you think caused it.
  • The person who had the side-effect.
  • Your contact details as the reporter of the side-effect.

It is helpful if you have your medication and/or the leaflet that came with it with you while you fill out the report.