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Medicines management

Exploring the effects of orlistat and guidance on its use to achieve weight loss in patients

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Orlistat inhibits the action of gastrointestinal lipases. Normally, these break down dietary fat into absorbable free fatty acids and monoglycerides. By inhibiting this breakdown, orlistat reduces the amount of fat that is absorbed, so helps patients lose weight.

Who should take orlistat?

Alli should only be used in patients over 18 who have a BMI of 28kg/m2 or more (Electronic Medicines Compendium (EMC), 2009a). A height measure and calibrated weighing scales are needed to calculate a patient’s BMI. Xenical has been reviewed in a NICE clinical guideline, and should be used in patients with a BMI of 30kg/m2 or more, or in patients with a BMI of 28kg/m2 or more with associated risk factors (NICE, 2006).

There is no information on the use of orlistat when pregnant or breastfeeding, so it should be avoided in these patients. It should also not be used in patients with cholestasis or chronic malabsorption syndrome.

Orlistat should be used in conjunction with a lower-fat, mildly hypocaloric diet. This diet should be nutritionally balanced, with fat providing 30% of the calorie intake, distributed over three main meals per day. It is recommended that the diet and an exercise programme should be started before beginning treatment with Alli, and this programme should continue once Alli is stopped.

Weight loss

Realistic weight loss targets should be discussed with the patient. NICE (2006) suggests a total weight loss of 5–10% and a maximum weekly weight loss of 0.5–1kg.

Alli should be taken in 60mg doses three times a day, just before or within one hour of meals. Xenical should be taken at the same time intervals, but in 120mg doses. If a meal is missed or contains no fat, the dose of orlistat should be omitted.

An assessment of the patient’s weight loss should be undertaken at 12 weeks.  For Alli, if the patient has not lost any weight then the use of Alli should be reviewed. If some weight loss has been achieved, its use can be continued for up to a maximum of six months. For Xenical, its use should only be continued if the patient has lost 5% of their original body weight. Treatment with Xenical should only be continued for more than 12 months if the benefits and limitations have been discussed with the patient.


The side-effects of orlistat are mainly related to undigested fat passing through the gastrointestinal tract. These side-effects include oily spotting, flatus with discharge, fatty/soft/liquid stools, faecal urgency and faecal incontinence. The likelihood of side-effects occurring can be minimised by adhering to a lower-fat diet.

Interactions with other products

Orlistat may decrease the absorption of other medicines. It has been shown that ciclosporin is affected in this way, so orlistat should not be given to patients on ciclosporin. It should also not be used by patients on oral anticoagulants as their international normalised ratio (INR) may be affected. It may reduce plasma levels of amiodarone, which may make dose adjustments necessary. Orlistat may also indirectly reduce the effectiveness of oral contraceptives by reducing absorption and possibly causing diarrhoea, so an additional contraceptive method is recommended while orlistat is taken. A multivitamin should be taken each night while on orlistat to ensure an adequate intake of fat soluble vitamins A, D, E and K (European Medicines Agency, 2009; EMC, 2009a; EMC, 2009b).


Indications for orlistat

To help weight loss in conjunction with a lower-fat, mildly hypocaloric diet.


  • For Alli (available without prescription), the patient should be over 18 with a BMI of 28kg/m2 or more
  • For Xenical (prescription-only product), the patient should have a BMI of 30kg/m2 or more, or 28kg/m2 or more with associated risk factors
  • BMI = weight (kg) divided by height (m2)
  • Discuss realistic weight loss targets:

5–10% weight loss overall

Maximum 0.5–1kg per week (NICE, 2006)

  • Assess weight loss at 12 weeks:

Only continue Alli if weight loss has been achieved, and use for a maximum of six months

Only continue Xenical if a weight loss of 5% of original weight has been achieved. The drug should only be continued after one year if the potential benefits and limitations have been discussed with the patient


David Abbott MRPharmS, is Senior Pharmacist – Medicines Information, Chesterfield Royal Hospital NHS Foundation Trust

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