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Orlistat (Xenical)

Orlistat is a drug that is available on prescription for people with obesity.

  • Orlistat reduces the amount of fat that your body can absorb from food in your diet.
  • It encourages you to follow a low-fat diet, otherwise you experience the unpleasant side effects of fat passing through your digestive system without being absorbed.
  • The side effects of eating fatty foods while taking Orlistat include stomach pain, bloating, fatty stools and diarrhoea.


When combined with a low fat and low calorie diet and lifestyle changes, Orlistat can produce moderate weight loss.

There are certain conditions under which Orlistat can be prescribed, according to guidelines from the organisation NICE. NICE (the National Institute of Clinical Excellence) makes recommendations about safe practice in healthcare.

According to the NICE Obesity Guidelines, which were last amended in 2010, Orlistat can be considered for:

  • adults with a BMI of 30 or more
  • adults with a BMI of 28 or more if there are associated risk factors such as high cholesterol or high blood pressure.
  • Additionally, prescribing a drug treatment for weight management should only be considered after dietary, exercise and behavioural approaches have been started and evaluated.

Regular reviews are recommended to monitor the effect of the drug. The length of time you take the drug may depend on how effective it is at helping you to lose weight.

Occasionally, drug treatments may be used to maintain weight loss rather than to continue weight loss.

People who have used drug treatments to manage obesity should be offered continued support to manage their weight after the drug is no longer taken.



Alli is a weight loss drug that is available over-the-counter.


The over-the-counter Alli pill is a lower-dose version of Orlistat (Xenical). It can be bought by adults aged 18 and over with a BMI of 28 or greater. Pharmacists are required to weigh customers before they can sell the pills.

There are several groups of people who should not take the Alli pill, including:

  • people who have a problem with absorbing nutrients
  • pregnant or breastfeeding women
  • people taking other prescribed medicines such as ciclosporin, warfarin or other oral anticoagulants
  • people with some liver problems.


It is vital that you have a consultation with the dispensing pharmacist or professional to ensure that the Alli pill is right for you and that you have the right information and support to use it effectively.

During your consultation you’ll also have the opportunity to discuss your general health and cardiovascular risk factors, and to get a full assessment of your health needs.

Weight loss medicines should only ever be taken if you are also committed to making changes to your diet and lifestyle.
They should not be considered as a quick-fix stand-alone treatment.

Good to Know! The emphasis on long-term rather than quick-fix improvement might help you lose weight and keep the weight off.



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* Some information on this page has been produced with the kind permission of the British Heart Foundation, which is the joint copyright owner with Weight Concern

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