How Does Orlistat Work?

If you're exploring weight loss medicines, you may have come across Orlistat and want to know more. Our healthcare professionals have taken a deep dive to help you understand how Orlistat works, the benefits and side effects.

Article summary:

• Orlistat works by blocking some of the enzymes responsible for breaking down dietary fat, meaning less fat is absorbed by your body.
• Orlistat is different to other weight loss treatments because it's not made to suppress hunger and works best alongside regular exercise.
• Other medications you’re taking may be affected when you incorporate Orlistat into a weight management plan.

What is Orlistat?

Orlistat is a medicine that helps support weight management by reducing fat absorption in your body from food. This type of medication is known as a lipase inhibitor. Unlike some other weight loss treatments, it isn't designed to suppress appetite but instead works within your digestive system to help reduce the absorption of fat. [1]

When taken alongside a balanced, reduced-calorie diet and healthier lifestyle habits, Orlistat may help support gradual weight loss.

Normally, fat from your diet is broken down by enzymes in your stomach, and then absorbed into your body to be stored. Orlistat works by reducing the activity of these enzymes, meaning that some of the fat from your food passes through your digestive system without being absorbed, and instead passes out of your body in your bowel movements.

How does Orlistat compare to weight loss injections?

Orlistat and weight loss injections work differently.

Orlistat works in the digestive system and is designed to reduce the amount of dietary fat absorbed from food into your body. Weight loss injections, like GLP-1 receptor agonists, work by mimicking the hormones involved with appetite control and digestion, helping you to feel fuller for longer so you consume less calories.

Some of the main differences between Orlistat and weight loss injections include:

Can Orlistat help with weight loss?

Orlistat can support weight loss when combined with healthy lifestyle changes, but might not be effective for everyone, and shouldn’t be considered a shortcut to losing weight. Prioritising factors like healthy eating, exercise and a bedtime routine can have a greater impact on overall weight loss. [2]

A sustainable weight management plan usually includes:

• A balanced diet with reduced calories
• Regular physical activity
• Quality sleep and recovery time

How effective is Orlistat?

In a 2-year clinical trial, people taking Orlistat lost more weight on average than those taking placebo (a dummy pill), achieving a 10.2% reduction in body weight compared with 6.1%. This clinical trial also showed that those taking Orlistat maintained weight loss better than in the placebo group. [3]

For maximum effectiveness, 1 Orlistat capsule should be taken with each main meal (a maximum of 3 capsules a day) before, during, or up to 1 hour after each meal. If you miss a meal or the meal does not contain any fat, you don't need to take the capsule.

How do I take Orlistat?

Orlistat is usually only taken with meals that contain fat. There are two types of treatments: Xenical and Alli.

• Xenical is the prescription dose which contains 120mg of Orlistat.
• Alli is available over-the-counter and contains 60mg of Orlistat.

Both treatments target weight loss in exactly the same way. Take one capsule within an hour of eating each of your three main meals. One at breakfast, one at lunch and one at dinner.

You should continue taking Orlistat for at least three months to notice any changes. If you haven’t lost 5% of your initial body weight within three months, continuing is not recommended and you should speak to your prescriber. Orlistat works best if you're eating a moderate-fat, reduced-calorie diet. If your diet is higher in fat, you may not see weight loss even if the drug is working mechanically.

Who is eligible to take Orlistat?

It’s important to know which weight loss treatment works for you, and Orlistat isn’t suitable for everyone. In the UK, adults with a body mass index (BMI) of 30kg/m² or above, or people with existing weight-related conditions can be eligible for an Orlistat prescription.

Some conditions such as:

• High blood pressure
• Type 2 diabetes
• Sleep apnoea
• High cholesterol

What foods can I eat while taking Orlistat?

It's important to eat foods with only a moderate amount of fat when taking Orlistat. Avoid high-fat foods like processed meat, fried meals or sugary snacks like cake and biscuits.

Fortunately, healthy eating doesn't need to be complicated. You could consider:

• Lean sources of protein (turkey breast, chicken and salmon)
• Fruit and vegetables (avocado, olives and soybeans)
• Whole grains (oats, quinoa and almonds)
• Lower-fat dairy options (skimmed milk and plain yogurt)

How to get the most from your Orlistat treatment

Make gradual changes to reduce your calorie intake, such as choosing smaller portions and limiting high-calorie foods. Many people are advised to aim for around 600 fewer calories per day than they would normally eat. [4]

Increasing your physical activity with regular exercise can also improve your weight loss results with Orlistat. 30 minutes of moderately intense workouts over 5 days is a recommended good place to start.

What are my targets?

Successful weight loss depends on realistic, achievable goals. When you start taking Orlistat, your first weight loss target could be to lose 5% of your weight in the first 3 months. If you succeed in losing the weight, you'll be able to continue with the treatment.

However, don't be disheartened if you don't lose weight with Orlistat. After a break of 6 months, you can either try again or explore other types of weight loss medication to find what works for you.

What are the side effects of Orlistat?

Side effects related to Orlistat are mainly related to the reduced absorption of fat which passes out in the faeces. The symptoms are often mild and not everyone experiences them, but keeping to your low-fat diet will reduce the risk of side effects occurring. [5]

The side effects you could experience may include:

• Stomach pain/discomfort
• Passing wind
• Loose, oily stool
• Oily spotting from your bottom
• Going to the toilet more often
• Headache
• Bloating
• Fatigue

These symptoms often improve after a few weeks when your body has adjusted to the new medicine.

How will Orlistat affect other medications?

As Orlistat affects absorption into your digestive system, other medications* may be affected, especially if you experience diarrhoea. It's very important to check with your doctor or pharmacist first before taking Orlistat if you're taking other medications, such as the oral contraceptive pill. If you’re taking an oral contraceptive pill and experience severe diarrhoea, you should use an additional method of contraception, such as a condom. It's also a good idea to consult your doctor if you:

• Are pregnant or breastfeeding
• Have problems absorbing food
• Have reduced bile flow
• Are allergic to any inactive ingredients in Orlistat (including gelatine)

*Cyclosporine, aevothyroxine, anticoagulants, amiodarone, antiepileptics and antiretrovirals.

Can I take vitamins?

Yes, you should take a multivitamin containing fat-soluble vitamins (A, D, E, K and beta-carotene) while taking orlistat long-term, because Orlistat reduces absorption of these vitamins

It's strongly recommended that you take a multivitamin containing these at least two hours before or after you've taken your Orlistat dose of the day. Most doctors recommend you take your multivitamin at bedtime to help with absorption. [6]

If you’ve decided to try Orlistat, the next step might be to work out your diet.

Speak to our healthcare professionals to explore our Orlistat diet plan.

At MedExpress, we offer online consultations with regular clinical check-ins, and a range of weight loss treatments including Orlistat, Mounjaro Pen, Wegovy Pen and Wegovy Pill, and our team can help you find the right treatment for you.

References

1. NHS website. Orlistat [Internet]. nhs.uk. 2026. Available from: https://www.nhs.uk/medicines/orlistat/
2. Sharma S, Kavuru M. Sleep and Metabolism: An Overview. International Journal of Endocrinology [Internet]. 2010 Aug 2;2010(270832):1–12. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2929498/
3. Sjöström L, Rissanen A, Andersen T, Boldrin M, Golay A, Koppeschaar HP, et al. Randomised placebo-controlled trial of orlistat for weight loss and prevention of weight regain in obese patients. European Multicentre Orlistat Study Group. Lancet (London, England). 1998 Jul 18;352(9123):167–72.
4. Dietary advice whilst taking Orlistat | NHS Lanarkshire [Internet]. Available from: https://www.nhslanarkshire.scot.nhs.uk/patient-information-leaflets/nutrition-dietetics/pil-dietad-22-12321-l/
5. NHS website. Orlistat [Internet]. nhs.uk. 2026. Available from: https://www.nhs.uk/medicines/orlistat/
6. McDuffie JR, Calis KA, Booth SL, Uwaifo GI, Yanovski JA. Effects of Orlistat on Fat-Soluble Vitamins in Obese Adolescents. Pharmacotherapy. 2002 Jul;22(7):814–22.