Orlistat Side Effects: How to Manage Them

If you're taking orlistat to support your weight loss, knowing what side effects to expect and how to manage them can make a real difference to your experience of the treatment. The good news is that orlistat side effects are well understood, mostly digestive in nature, and significantly reduced by following a low-fat diet.

What Are the Most Common Orlistat Side Effects?

The vast majority of orlistat side effects are gastrointestinal, and they're directly connected to how the medication works. Orlistat blocks around a third of the fat you eat from being absorbed by your body.¹ That undigested fat passes out in your stools. The more fat you eat, the more pronounced the effects.

According to the orlistat prescribing information, the following effects are classified as very common (affecting more than 1 in 10 people):¹

• Oily or fatty stools
• Oily spotting on underwear
• Flatulence (wind), sometimes with discharge
• An urgent need to open your bowels
• Increased frequency of bowel movements
• Liquid or loose stools
• Abdominal discomfort or pain
• Headache

These effects tend to be most noticeable in the first few weeks of treatment and typically reduce as you adjust your diet to contain less fat.¹ They're a signal that the medication is working, not a sign that something is wrong.

Why Does Diet Make Such a Big Difference?

The single most effective way to reduce orlistat side effects is to reduce your dietary fat intake. Clinical guidance is clear that the likelihood of gastrointestinal effects increases when orlistat is taken alongside a high-fat diet.¹

NHS guidance recommends that no more than approximately 30% of your daily calorie intake comes from fat.⁶ In practice: no more than 20g of fat per meal, spread evenly across three meals a day. Eating most of your daily fat in one sitting significantly increases the risk of side effects.

Foods to avoid on orlistat (or keep to very small portions):

• Fried foods (chips, fried chicken, battered fish)
• Full-fat dairy (butter, cream, full-fat cheese)
• Fatty cuts of meat (bacon, sausages, lamb chops)
• Pastries, croissants, and pies
• Crisps, chocolate, and creamy sauces
• Takeaways and fast food

Practical swaps that reduce your fat intake quickly:

• Choose lean cuts of meat and remove visible fat before cooking
• Grill, bake, poach, or steam rather than frying
• Switch to semi-skimmed or skimmed milk and reduced-fat dairy products
• Use a low-fat spread instead of butter
• Check labels on sauces and ready meals and aim for less than 5g of fat per 100g

The relationship is straightforward. Less dietary fat means less unabsorbed fat passing through your system, and fewer side effects as a result. For more ideas on keeping your meals low in fat while taking orlistat, take a look at our guide to 5 Simple Meal Swaps for Weight Loss.

How to Manage Specific Orlistat Side Effects

Oily stools and spotting

Oily stools are the most commonly reported effect and are caused by unabsorbed fat passing through the bowel. Reducing your fat intake at each meal is the most reliable fix. These effects typically improve significantly after the first few weeks as your dietary habits adjust.

Wind and urgency

Flatulence and urgency to use the toilet can feel unpredictable early in treatment. Eating smaller meals, avoiding high-fat snacks between meals, and not taking orlistat without food all help to keep things predictable. The prescribing guidance states that the dose should be omitted entirely if a meal is missed or contains no fat.¹

Abdominal discomfort

Mild cramping and abdominal discomfort are common and usually settle as your gut adjusts. Staying well hydrated, eating slowly, and not overloading any single meal with fat will help. If abdominal pain is severe or persistent, speak to your GP or prescribing pharmacist.

Headache

Headaches are listed as very common in the clinical trial data.¹ Staying hydrated and eating regular, balanced meals supports overall wellbeing during the adjustment period. Standard over-the-counter pain relief such as paracetamol is appropriate for short-term management.

Will Orlistat Affect My Vitamin Absorption?

Yes. Because orlistat reduces the absorption of dietary fat, it can also reduce the absorption of fat-soluble vitamins: A, D, E, and K. These vitamins are carried into the body dissolved in dietary fat, so blocking fat absorption can lower their uptake too.¹

The prescribing guidance notes that a multivitamin supplement like OneVit Complete Multivitamin could be considered for patients on orlistat. If you do take a multivitamin, take it at least two hours before or after your orlistat dose, or simply at bedtime, to allow it to be absorbed properly.¹ This is especially relevant if you're eating less overall, as micronutrient intake may already be lower on a reduced-calorie diet.

Are There Any Medications That Interact With Orlistat?

Orlistat can affect how several medications are absorbed in the gut. The following interactions are worth being aware of:¹

• Anticoagulants (e.g. warfarin): orlistat may affect INR levels. If you're on warfarin, your coagulation should be monitored closely.
• Anticonvulsants (e.g. valproate, lamotrigine): there have been reports of convulsions in patients taking these alongside orlistat. Tell your prescriber if you're on epilepsy medication.
• Levothyroxine (thyroid medication): rare cases of reduced thyroid control have been reported. Your GP may want to monitor thyroid levels.
• Ciclosporin: co-administration is not recommended due to reduced ciclosporin blood levels.
• Combined oral contraceptive pill: if you experience severe diarrhoea while taking orlistat, the pill may be less reliably absorbed. Use additional contraception (such as condoms) during episodes of severe diarrhoea.

Always tell your GP, pharmacist, or prescribing clinician about all medications you're taking before starting orlistat.

What Are the Less Common but Serious Side Effects?

The following side effects are uncommon or rare, but are important to be aware of:¹

• Liver problems (hepatitis): very rare, but cases have been reported. Symptoms to watch for include yellowing of the skin or eyes (jaundice), dark urine, itching, or upper abdominal pain. Stop taking orlistat and seek urgent medical advice if these develop.
• Kidney problems (oxalate nephropathy): rare. The risk is higher in people with existing kidney disease or dehydration.
• Rectal bleeding: uncommon. Contact your GP if you notice blood in your stools or rectal bleeding.
• Pancreatitis: rare. Symptoms include severe upper abdominal pain that may radiate to the back, along with nausea and vomiting.
• Gallstones (cholelithiasis): reported in some patients, with frequency not yet fully established.

These effects are rare, but knowing the warning signs means you can seek help promptly if needed.

When to Seek Further Advice

Contact your GP or prescribing clinician if:

• You experience yellowing of the skin or eyes, dark urine, or severe abdominal pain
• You notice rectal bleeding or blood in your stools
• Your side effects are severe, persistent, or significantly affecting your daily life
• You develop severe diarrhoea while taking the combined contraceptive pill
• You are on anticoagulants, anticonvulsants, or levothyroxine and have concerns about how orlistat may affect them
• You haven't lost at least 5% of your starting body weight after 12 weeks of treatment

A full list of known side effects and drug interactions is available in the patient information leaflet supplied with your medication.

Frequently Asked Questions

Do orlistat side effects go away?

For most people, yes. Gastrointestinal effects are typically most noticeable in the first few weeks and reduce significantly as dietary habits adjust. Clinical trial data confirms that the incidence of side effects decreases with prolonged use.¹ The key is keeping dietary fat low and consistent.

Can I take orlistat if I have IBS?

This is worth discussing with your GP before starting. Orlistat's gastrointestinal effects can overlap with IBS symptoms and may make them harder to distinguish. Your GP can help you weigh up whether orlistat is appropriate for your circumstances.

Is Orlos a different medication to orlistat?

Orlos is a branded version of orlistat. It contains the same 120mg active ingredient and works in exactly the same way. The side effect profile is identical. Some patients are prescribed or sold orlistat under different brand names, but the medication itself is the same.

Should I stop taking orlistat if I get side effects?

Not necessarily. Mild gastrointestinal effects are expected and manageable with dietary adjustments. If symptoms are severe or distressing, speak to your pharmacist or GP before stopping.

Can I drink alcohol on orlistat?

Alcohol itself doesn't directly interact with orlistat, and there's no known interaction between the two.¹ That said, alcoholic drinks (particularly beer, wine, and cocktails) are often consumed alongside high-fat foods, which is what causes side effects. Alcohol can also lower your willpower to stick to a low-fat diet, so moderation is sensible. There's no clinical reason to avoid alcohol entirely, but drinking heavily while on orlistat is likely to make side effects worse.

What happens if I accidentally eat a high-fat meal on orlistat?

You're likely to experience more pronounced side effects: oily stools, urgency, and flatulence are the most common. This is uncomfortable but not dangerous. Return to your low-fat diet at your next meal.

References

1. Neon Healthcare Ltd. Orlistat 120mg hard capsules – Summary of Product Characteristics. Electronic Medicines Compendium (eMC). Last updated October 2023. Available at: https://www.medicines.org.uk/emc/product/2592/smpc
2. NHS Inform. Orlistat. NHS. Last reviewed February 2026. Available at: https://www.nhsinform.scot/tests-and-treatments/medicines-and-medical-aids/types-of-medicine/orlistat/
3. Highlights of Prescribing Information. Orlistat. StatPearls, National Center for Biotechnology Information. Last updated February 2024. Available at: https://www.ncbi.nlm.nih.gov/books/NBK542202/
4. Patient.info. Orlistat (Weight Loss Medicine): Uses and Side-Effects. Last reviewed June 2024. Available at: https://patient.info/healthy-living/obesity-overweight/orlistat-weight-loss-medicine
5. NHS Lanarkshire. Dietary advice whilst taking Orlistat. Available at: https://www.nhslanarkshire.scot.nhs.uk/patient-information-leaflets/nutrition-dietetics/pil-dietad-22-12321-l/
6. South West Yorkshire NHS. Primary Care Orlistat Prescribing and Review Guidelines for Adults. Available at: https://best.barnsleyccg.nhs.uk/media/momgdvqe/orlistat.pdf

This article is intended for informational purposes only and does not replace professional medical advice. Always read the patient information leaflet supplied with your medication and speak to a healthcare professional if you have specific concerns.

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