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Orlistat 120mg side effects

With Orlistat, your plate decides your side effects. The capsule stops about a third of the fat in a meal being absorbed, and the unabsorbed fat leaves through the bowel.

By Gary Atmos, Penzilla Editorial Team. Last reviewed 8 October 2026.

What people notice

Oily marks on underwear. Oily wind. A sudden need for the toilet. Pale, greasy stools. Stomach cramps. All of these trace back to fat passing through.

The fat rule

A low fat meal brings mild effects or none. A takeaway brings the worst. Aim for roughly 30% of calories from fat, split across your meals. No fat in the meal, or no meal? Leave the capsule out.

A fat budget per meal

On 2,000 calories a day, 30% from fat is about 67g. Split across three meals, aim for roughly 22g of fat per meal. Read labels: a single pastry can hold the whole amount.

Timing the capsule

Right before the meal, during, or within the hour afterwards. Later than an hour and the capsule misses the fat.

The vitamin rule

Vitamins A, D, E and K dissolve in fat, so Orlistat lowers how much you absorb. Take a multivitamin at bedtime, well away from your last capsule.

Medicines which clash

Mention Orlistat to a pharmacist if you take warfarin, ciclosporin, levothyroxine, epilepsy medicines or HIV medicines. Take levothyroxine and Orlistat at least four hours apart. If Orlistat gives you severe diarrhoea, the contraceptive pill may fail, so add a barrier method.

Stop and seek advice

Yellow skin or eyes, dark urine, or severe stomach pain are reasons to stop and speak to a doctor. Report reactions on the Yellow Card site.

60mg is gentler

Alli, the 60mg capsule, blocks less fat and tends to cause milder effects. Orlistat cost and options.

Questions people ask

Sources

1. Cheplapharm, Xenical 120mg Summary of Product Characteristics (electronic medicines compendium)
2. NHS, Obesity: treatment
3. MHRA, Yellow Card reporting site