myBMI colour logo

Join the community

What are the Side Effects of Orlistat?

Are you concerned about the potential side effects of Orlistat? Find out more about the most common side effects of your weight loss treatment.
man on toilet seat

If you’ve been considering taking Orlistat capsules for weight loss you may have heard about some of the side effects this medication can cause.

Some of this information can be a little off-putting, especially if you’ve never taken weight loss medication before, which is why we’re here to ease your mind.

We’re going to explain the side effects of Orlistat, how some of them can be prevented, and how you’ll be able to gauge whether this is the right medication for you long term.

Let’s begin by explaining what the most common side effects are, so you’ll know what to look out for.

What are the side effects of 120mg of Orlistat?

Like most medications, Orlistat has quite a few potential side effects, no matter what strength you take.

Some of these side effects are more common than others, with the most common affecting more than 1 in 10 patients.

These very common side effects include:

  • Headaches
  • Abdominal pain or discomfort
  • An urgent or increased need to poo
  • Flatulence (wind) with discharge
  • Oily discharge
  • Oily or fatty poo
  • Liquid poo
  • Low blood sugar levels in some patients with type 2 diabetes

If you’ve been looking into Orlistat as a potential weight management aid, you’ll probably have heard about the oily discharge and fatty poo, which we’ll explain more about later.

First, we’re going to let you know more about the other common side effects of Orlistat, which are thought to affect 1 to 10 patients out of every 100:

  • Rectal pain or discomfort
  • Soft poo
  • Inability to control when you poo (faecal incontinence)
  • Bloating in some patients with type 2 diabetes
  • Tooth or gum disorder
  • Irregular periods
  • Tiredness

Now, before we move on it’s important to mention that these aren’t the only possible side effects of Orlistat, just the most common.

There are other potential side effects, but there isn’t enough data to estimate how common they are amongst patients.

You should familiarise yourself with these if you are given Orlistat by a prescriber or pharmacist, and they can all be found in the patient information leaflet included with your medication.

Why does Orlistat cause oily poo and discharge?

Now to address that fatty poo and oily discharge you’ve heard so much about (a pleasant topic, we know).

These side effects happen because of how Orlistat works to help you lose weight.

When you take Orlistat it binds up to a third of the fat you eat, keeping it from being digested and passing it out of your system.

Now, that fat has to go somewhere, and there’s only one way out — with your poo.

Usually, this will pass in a normal, if not a little soft, poo but if you eat more than the recommended amount of fat while taking Orlistat you will probably experience side effects.

With more fat to pass from your system, it can be a little too much to pass with a regular bowel movement alone, which is when you’ll notice oily, often orange, discharge in the toilet, or in your underwear after you break wind.

Put it this way, what goes in, must come out, and if you eat more fat than recommended there will be more for your body to get rid of.

Is there a way to prevent the side effects of Orlistat?

Yes, there is a way to help prevent that oily poo and discharge, and it’s surprisingly simple — you should follow the dietary guidelines set out by the manufacturer or Orlistat itself.

The patient information leaflet recommends that your diet is made up of no more than 30% fat.

This can be a little difficult to gauge by yourself, so here are some guidelines for how much fat you should be eating depending on your current daily calorie intake:

Daily Calorie IntakeAmount of Fat Per MealTotal Amount of Fat Per Day

Of course, these are just guidelines rather than hard and fast rules, but they’re a good start when you’re trying to work out how much fat you should be eating while taking Orlistat.

If you have any questions or are at all uncertain about your treatment, speak to your prescriber, local pharmacist, or another medical professional for advice.

They’ll be able to help you get your fat intake to a place that will work within your diet while keeping your side effects to a minimum.

Does Orlistat cause diarrhoea?

Diarrhoea isn’t a known side effect of Orlistat at the moment.

However, as digestional problems are some of the more common side effects of this medication, we can’t say that diarrhoea is completely out of the question.

In fact, difficulty controlling when you poo or needing to poo urgently are both common side effects people experience during treatment, so you could be forgiven for thinking that diarrhoea is included within that lovely set of experiences.

Should I seek medical help if I experience side effects?

If you experience side effects of any medication, including Orlistat, you should speak to a medical professional, such as your prescriber or local pharmacist.

They will be able to assess your current medical state and whether you should continue your treatment.

If your side effects are severe then you may need to seek emergency medical assistance, which may include going to your local A&E or calling 999, depending on your symptoms.

Serious side effects that you should look out for if you are taking Orlistat include:

  • Symptoms of an allergic reaction, e.g. swelling of the face, lips, tongue, or throat, itching, hives, difficulty breathing or swallowing
  • Bleeding from your back passage
  • Symptoms of inflammation in your large intestine, e.g. lower stomach pain, fever, constipation
  • Skin blistering
  • Symptoms of gallstones, e.g. severe stomach pain
  • Symptoms of inflammation of the pancreas, e.g. severe abdominal pain sometimes radiating towards the back, fever, nausea, vomiting
  • Symptoms of Hepatitis, e.g. yellowing of the skin and whites of the eyes, itching, dark coloured urine, stomach pain, liver tenderness, loss of appetite
  • A build up of calcium oxalate which may lead to kidney stones

Does this medication affect your kidneys?

Using Orlistat can cause kidney stones in some cases, most commonly in patients who already suffer from chronic kidney problems.

If you have kidney disease or any kidney problems, you should tell your prescriber or pharmacist about this during your consultation for weight management treatments.

This is one of the many things they may need to know about while deciding which weight loss medication could be right for you.

If you have kidney disease, your prescriber may not be comfortable providing Orlistat for you and may suggest an alternative medication like Saxenda or Wegovy.

Now you’ll know which symptoms to look out for during your weight management treatment with Orlistat and when you should get emergency medical assistance.

Remember, if you’re ever unsure you should speak to a medical professional — they can help you get on the right track.

If you’d like to learn more about Orlistat and other weight loss medications that are available, why not check out some of our other articles?

We’ve picked out a couple of our favourites that we think you’ll find interesting too.

Content Written By

Laura Henderson

Laura Henderson

Reviewed & Fact-Checked By

Table of Contents

myBMI colour logo heart

Content Written By

Reviewed & Fact Checked by

James O'Loan

James O'Loan

How we ensure accuracy in our content

More Content We Think You'll Love

Foods to avoid on Mounjaro
Diet & Nutrition Advice

When to eat and foods to avoid while taking Mounjaro

As we know, when undergoing any weight loss treatment, it’s always best to have a healthy diet and lifestyle to boost treatment and get the full effect. But each treatment has slightly different effects on the body and metabolism, meaning sometimes the average “healthy diet” doesn’t always work the best. There are certain foods and drinks that you should be avoiding whilst taking Mounjaro for weight loss.

Read More »