Orlistat is a medication designed to help you lose weight. It binds to the fat in your meals, preventing it from being digested. However, as with any medication, some patients will experience side effects when using it.

Before You Take Orlistat

Before taking any new medication, you should speak with your GP, and read through the Patient Information Leaflet. This allows you to know the risks you may face before you start a course of medication.

This medicine must not be taken by children and adolescents under 18 years old. 

Do not take orlistat if you;

  • Are allergic to orlistat or any of the listed ingredients

  • Are pregnant or breastfeeding

  • Have cholestasis (a block in the flow of bile from the liver) or chronic malabsorption syndrome

  • Are currently taking warfarin (or other blood thinners) or ciclosporin 


Talk to your doctor before using orlistat if you;

  • Have diabetes

  • Currently have or have previously had problems with your kidneys – orlistat may be associated with kidney stones in cases of chronic kidney disease.

  • Are taking or plan to take any other medications – orlistat can interfere with how much you are able to absorb.

    • The oral contraceptive pill may be less effective if you take orlistat and experience severe diarrhoea. Use an extra method of contraception while using orlistat.

    • Take a multivitamin at bedtime when you are using orlistat every day. Orlistat can prevent you from absorbing some vitamins from your food; taking it at bedtime should allow it to fully digest.

  • Are taking any of the following medications;

    • Amiodarone (for heart rhythm problems)

    • Acarbose (to treat type 2 diabetes)

    • Levothyroxine

    • Medications for high blood pressure or high cholesterol

    • Medications to treat epilepsy, HIV, depression, psychiatric problems or anxiety.


Common Side Effects

As with any medication, some patients will experience side effects when taking orlistat.

As a fat binder, orlistat prevents your body from absorbing around ⅓ of the fat in your diet. This fat is expelled in your faeces, which means the most common side effects are often gastrointestinal in nature. If you experience these effects, you can try eating less fat in your diet, though you may still experience these effects for as long as you use this medication.

More than 1 in 10 people may experience;

  • Flatulence, with or without oily spotting

  • Fatty, oily or soft stools

  • Sudden bowel movements


Up to 1 in 10 people may experience the following;

  • Abdominal pain

  • Anxiety

  • More frequent bowel movements

  • Runny or liquid stools

  • Incontinence


If any of these effects become severe or troublesome, speak to your doctor or pharmacist.


Serious Side Effects

These effects are less common than the above ones; it is not known how frequently they occur in patients. Some of these conditions are complex, with multiple possible symptoms.

  • Severe allergic reaction

    • Breathing difficulties, sweating, rashes, itching, swelling of the face, rapid heart beat, fainting or collapse

    • If you experience any of these effects, stop using this medication and seek urgent medical assistance

  • Bleeding from the rectum

  • Inflammation of the large intestine (diverticulitis)

    • Abdominal pain, particularly on the left side, fever, constipation

  • Pancreatitis

    • Severe abdominal pain, pain that radiates towards the back, fever, nausea, vomiting

  • Skin blistering

  • Inflammation of the liver (hepatitis)

    • Yellowing of the skin and/or eyes

    • Dark coloured urine

    • Loss of appetite

    • Itching

    • Stomach pain

    • Tenderness around the liver

  • Build up of calcium in the kidneys (oxalate nephropathy)

    • Kidney stones


If you experience any of these side effects, stop taking orlistat and speak to your doctor.


Long Term Side Effects

It has been noted that orlistat may have some effects on blood tests while it is taken, which may last for a time after you stop taking it.

  • Increase in liver enzyme levels

  • Effects on blood clotting in people taking blood thinning medication (warfarin)


If you go for a blood test, inform your doctor that you are taking orlistat, or if you have used it in the past.


More Information

Orlistat is available as a first-line treatment on the NHS – they have a great deal of resources for patients taking orlistat, found here.

For a more in-depth look at the advice, you can also read these dietary guidelines for patients using orlistat, also from an NHS source.


How to Reduce the Risk of Side Effects

The most common side effects of orlistat come from the removal of fat from the food you eat. Such side effects in the first few weeks of treatment can be a sign that you haven’t removed enough fat from your diet.

For best results, start your lower-fat diet a few days or a week before you start taking the medication. Find out how much fat your favourite foods contain, and work out the rough size of your usual portions.

This will help you establish a baseline for how much fat you are eating, and whether you may need to swap to a lower-fat alternative, preventing you from accidentally having too much fat in a single meal.

Orlistat is taken three times a day, with each main meal; make sure to spread your allowed amount of fat across these three meals. “Saving up” fat will only make that meal have worse side effects than the others, rather than allowing you to bank up the effects.

Many users find that the common side effects can be controlled by watching their diet and adjusting it as necessary.


How Long Can You Stay on Orlistat?

Orlistat should only be used for more than three months if you have lost at least 5% of your body weight while using it. 

A normal treatment course is around 3 months, after which a pharmacist will review your weight loss. If they decide to allow you to continue, the maximum length of treatment is around two years. Safety trials for taking orlistat for longer than 2 years have not been conducted, so most pharmacists will not prescribe after this length of treatment.


What Happens When You Stop Taking Orlistat?

Stopping orlistat is relatively easy; just stop taking the pills with your meals. Some effects may last for a few days, as the medication leaves your system. Many patients have reported putting back on some of the weight they have lost over the course of treatment, though this can be mitigated by sticking closely to your new diet plans.

There are no currently reported withdrawal effects from orlistat, though if you notice any changes, speak to your doctor. If you notice any changes, speak to your doctor.