Orlistat

How it works

It inhibits gastric and pancreatic lipases within the gastrointestinal tract, reducing the breakdown and absorption of dietary fat, which is then excreted.

Prescribing in practice

• Gastrointestinal effects such as oily stools, faecal urgency and flatulence are common and are worsened by a high-fat diet, so a lower-fat diet is essential.
• It can reduce absorption of fat-soluble vitamins, so a multivitamin taken at bedtime is often recommended.
• It may reduce absorption of some medicines, including ciclosporin, levothyroxine and certain antiepileptics, and may affect oral contraception if severe diarrhoea occurs.

Monitoring

Monitor weight response and review at intervals, continuing only if a meaningful weight loss is achieved within the recommended period.

Counselling the patient

• Follow a reduced-fat diet to gain benefit and minimise the unpleasant gastrointestinal effects.
• Take a multivitamin at bedtime to maintain fat-soluble vitamin intake.
• Use additional contraceptive precautions if severe diarrhoea occurs, and separate from levothyroxine dosing.

Evidence & guidelines

Orlistat is recommended by NICE as a pharmacological adjunct to lifestyle measures in obesity when defined weight-loss targets are met.