Table of contents
Medically reviewed by
Dr Daniel Atkinson
GP Clinical Lead
on August 02, 2022.
Meet Daniel  
Was this article useful?

How does orlistat work?

Orlistat is a lipase inhibitor. Lipase is an enzyme in your digestive system that helps you to break down any fat you eat in your meals and snacks, which it stores as energy for you to use later.

When you take orlistat it stops lipase from working, making it difficult for your body to digest and store fat. This is why you’ll need to follow a low-fat diet when you’re taking these tablets. Eating too much fat whilst taking orlistat can increase your risk of getting stomach problems. Equally, the medication won’t work at all if you completely cut fat out of your diet.

Alli works in exactly the same way as Xenical and Prolistat, but it’s just a smaller dose.

What does orlistat look like?

Both Xenical and Prolistat are branded blue capsules, with the name of the drug and the dosage imprinted on the side of it.

Alli tablets are also blue, with the name and dose on the side of the tablet.

How to take orlistat

The maximum daily dose for the medication is 360mg. That’s based on taking one 120mg capsule three times a day. The instructions for taking Prolistat and Xenical are usually the same, but your clinician will be able to advise you best.

It’s best to take orlistat with each meal you have that has fat in it, either:

  • just before you’re about to eat,
  • with your meal,
  • or up to one hour after you’ve finished eating.

If you skip a meal, or you forget to eat, you don’t need to take a tablet. If you know you’re eating a meal that contains no fat at all then you don’t need to take a tablet then, either.

When is the best time to take orlistat?

The best time to take Prolistat or Xenical is at meal times. The simplest way to do it is to have your three doses with your main meals - breakfast, lunch and dinner. You can take it just before food, with your meal or up to one hour afterwards.

How do I get the best results from orlistat?

To get the best results from orlistat, take it with food. The meal that you eat has to meet certain criteria for the medication to work. You’ll have to follow a low fat diet, but it’s important your meal does contain a little essential fat. If you’re eating a meal that has no fat in it at all, then it’s best not to take your tablet, as it won’t work.

How long does orlistat take to work?

If you follow the right diet, and take it as you’ve been prescribed to, you should find that Xenical and Prolistat start to work pretty fast - you could start to see results after two weeks.

How long should I take orlistat for?

How long you take orlistat for depends on your weight loss goals and how long it takes you to reach them. Generally speaking, you shouldn’t take orlistat for longer than three months, as if you haven’t achieved your weight-loss goals within this time, you should perhaps consider using alternative methods. You should also stop taking orlistat if you’ve reached a healthy weight.

Is orlistat effective?

Yes. In a clinical study, obese patients with a BMI of over 30 were given 120mg or orlistat three times a day. On average they lost 4.65kg, almost 5cm from their waist circumference and reduced their cholesterol levels by 10.6mg.

Does orlistat burn existing fat?

Orlistat doesn’t burn existing fat, it works to try to stop you from gaining more from the foods you eat. But, by stopping you from absorbing all the calories from the foods you eat, you’ll find it easier to maintain a calorie deficit, forcing your body to make use of its fat stores for energy.

Does orlistat suppress your appetite?

Orlistat isn’t an appetite suppressant. It will simply limit the amount of fat you can absorb from your diet and the meals you eat. When you take it to help you reach your weight-loss goals it can encourage healthier eating habits in the long-term, and encourage you to eat less fat once you’ve stopped taking it.

Is orlistat safe?

Orlistat is a very safe treatment to take. Some people might experience a few side effects, such as stomach issues, but these usually stop after a few weeks. Check with a clinician to make sure that it’s safe for you to use before you start taking it.

Is orlistat right for you?

choose-iocn-4Prolistat and Xenical are lipase inhibitors that work to block lipase from being produced by your body when you eat.

When you take either of these alongside a low fat-diet and exercise they can offer weight-loss benefits. The results you see from taking orlistat will depend on the dose you take and what your weight loss goals are. You can chat with our experts to see if this can be the right treatment for you.

Reference Popover #ref1
Reference Popover #ref2
Reference Popover #ref3
Reference Popover #ref4
This page was medically reviewed by Dr Daniel Atkinson, GP Clinical Lead on August 02, 2022. Next review due on August 01, 2024.

How we source info.

When we present you with stats, data, opinion or a consensus, we’ll tell you where this came from. And we’ll only present data as clinically reliable if it’s come from a reputable source, such as a state or government-funded health body, a peer-reviewed medical journal, or a recognised analytics or data body. Read more in our editorial policy.

What did you like about it?

What didn't you like about it?

Suggest a treatment

If there’s a particular treatment or condition you’re looking for, tell us and we’ll look into it for you.

We may email you about the problem, but you can opt out of these communications any time you like.

Ask or suggest something.

Submit your question here, or tell us if you’ve found an issue on our site.

We may email you about your query, but you can opt out of these communications any time you like.

Our average rating based on 3295 reviews.

Tell us about a problem

I accept the terms of use.
We may email you about the problem, but you can opt out of these communications any time you like.

We’ll get back to you very soon. We aim to respond to all queries in one working day.

You’re signed up to our newsletter. Keep an eye on your inbox for our latest update.


Sign up to our newsletter for all the latest on Weight Loss and more.

By clicking 'Subscribe now' you're agreeing to our Privacy Policy.