What is Orlistat and how does it work?

Orlistat is a medicine which can help you to lose weight if you are overweight or obese. It blocks enzymes in your gut which digest fat, stopping the digestion of 1/3rd of the fat that you eat. The undigested fat leaves your body in your stools (faeces).

Who can use Orlistat?

To be prescribed Orlistat, you must have:

  • Tried weight loss using conventional methods first (diet and exercise)

  • Your BMI:

    • Must be 30 or above; or

    • be 28 or above, and you have a medical condition that would benefit from you losing weight (such as diabetes, high blood pressure, high cholesterol).

You shouldn't take Orlistat if you are:

  • Pregnant

  • Breastfeeding

  • Under the age of 18 years.

  • Have a malabsorption syndrome.

  • Have cholestasis

What is the recommended dose?

The normal dose is one 120 mg capsule, three times a day with each meal. You do not need to take a capsule if there is no fat in that meal or if you miss a meal.

What are the side effects?

The main side-effects are caused by the fat that is excreted in your stool (faeces). This leads to smelly stools, flatulence, urgency to get to the toilet, or spotting on underwear. These side-effects settle with time and are less likely if you follow a low-fat diet. 

How long should treatment continue for?

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 you can stay on Orlistat. Our clinicians will review you regularly and will decide if it is still appropriate for you to continue on treatment. If you continue to lose weight after six months, your clinician may advise that you to continue taking Orlistat. This could be for up to 2 years, longer if you have a larger amount of weight to lose.

What results have been seen with Orlistat?

Studies have consistently shown that people taking Orlistat lose 3% more weight compared to diet alone in overweight and obese adults. Furthermore, the weight loss is maintained in the medium term in patients who continue therapy. As with any treatment, results vary from patient to patient, with others acheiving better results. 

Other health benefits:

  • Orlistat has been shown to improve glycaemic control in type 2 diabetes, reducing the risk of developing diabetes in overweight and obese individuals with impaired glucose tolerance.

  • Trials also showed small improvements in blood pressure and cholesterol than expected for the level of weight loss

Can I use it alongside other medication?

During your consultation, your clinician will go through your medical conditions and medications. This is important as Orlistat may be unsuitable if you are on other medications. 


Orlistat can interfere with the absorption of various medicines and vitamins and affect the way that they work. These include (but are not limited to HIV medication, Ciclospirin, Levothyroxine, Amiodarone, Warfarin, Antiepiletic drugs, acarbose and the contraceptive pill. ​



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©2020 by Dr Mariam Adegoke.