Orlistat (Xenical): how to take and how it works

What is Orlistat ?

Orlistat (Orlistate), better known by the trade name Xenical®, is a weight loss drug that acts by preventing the absorption of fats in the intestine.

Unlike most other drugs used in the treatment of obesity, orlistat is not a hunger suppressant, it only acts on the pancreatic enzymes that digest fat, being able to reduce the absorption of up to 1/3 of the fats consumed in the diet.

Orlistat is a medication indicated for people who need to lose weight and cannot do it through diet and exercise alone.

How it acts

The drug exerts its anti-obesity effect through inhibition of a pancreatic enzyme called lipase.

Lipase is the enzyme responsible for breaking ingested fats into smaller molecules, facilitating their absorption by the intestine. Without the action of lipase, the fat that reaches the intestines cannot be absorbed and is eliminated practically intact by the feces. Orlistat, therefore, prevents the digestion of fat and, consequently, its absorption by the body.

As its action is restricted to the gastrointestinal tract, and the drug is poorly absorbed by the body, orlistat has a very acceptable adverse effect profile. The main side effects are caused exactly by the large elimination of fat in the feces.

It is important to clarify that the drug is not able to prevent 100% the absorption of fats, an effect that, in fact, would not be desired, because our body needs this substance to function.

In general, Xenical prevents the absorption of 25% to 30% of ingested fat. This means that without an appropriate diet that restricts the consumption of fatty foods, orlistat does not have a relevant effect, because if the patient consumes much more fat than he needs, even with the 30% reduction in its absorption, a large amount will still be assimilated.

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In addition to aiding in weight loss, Xenical also reduces blood levels of glucose, uric acid, and LDL cholesterol, and helps treat hepatic steatosis and control blood pressure.


Orlistat should be used as complementary therapy for weight loss in patients with a body mass index greater than 30 kg/m².

The drug increases the effectiveness of the diet, helping the patient to lose, on average, 5 to 10 kg over a 12-month period.

Orlistat is also indicated for patients with a BMI above 27 kg/m² who have other diseases related to overweight, such as type 2 diabetes mellitus (or glucose intolerance), hypertension, dyslipidemia (high cholesterol), or hepatic steatosis.

Dosage – how to take

Xenical is sold in 120 mg tablets. The recommended dose is 1 tablet 3 times a day, during or right after each meal (breakfast, lunch and dinner). Doses higher than 360 mg per day (more than 3 tablets per day) do not show superior efficacy, so they are not indicated.

Xenical is considered the reference orlistat, but there are already similar drugs in Brazil, containing orlistat in 120 mg tablets. They are these: Orlistate, Lystate and Lipiblock.

Alli (not available in Brazil, only in Portugal) is sold in 60 mg capsules or 27 mg chewable tablets. The recommended dose is 1 tablet 3 times a day with each meal (breakfast, lunch and dinner).

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Since orlistat interferes with the absorption of fat-soluble vitamins (A, D, E and K), it is suggested that the patient take a vitamin supplement at night every day before going to bed.

The use of orlistat without a proper diet, with fat restriction, compromises the final result of the treatment. Therefore, the advice of a nutritionist is suggested as to the best diet to be taken during treatment.

Side effects

The most common side effect of orlistat treatment is the presence of fat droplets in stools. Other symptoms related to undigested fats are abdominal cramps, increased gas, increased number of daily bowel movements, and fecal incontinence. In general, the adverse effects are more easily controlled if the patient is disciplined in his diet. The more fats are ingested, the more common the undesirable effects will be.

Headache occurs in up to 30% of patients, back pain in 14%, flu symptoms in 40%, fatigue in 7%, anxiety in 5%, insomnia in 4%, pain to urinate in 8% and menstrual irregularity in up to 10% of women.

In the last 10 years, 13 cases of severe hepatic injury supposedly associated with the use of the drug have been described. So far, however, it has not been proven that the complication was directly caused by orlistat. It is worth noting that this drug has been used by more than 40 million people worldwide with no other reports of serious liver damage.

As with any drug, there are cases of allergic reactions, including anaphylaxis, like the use of Orlistat. However, these reactions are rare, occurring in less than 1% of cases.

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Drug Interactions

The following drugs may have their absorption altered by the use of orlistat:

  • Cyclosporine – an interval of at least 3 hours is required between administration of orlistat and cyclosporine.
  • Levothyroxine – an interval of at least 4 hours is needed between administration of orlistat and levothyroxine.
  • Multivitamins – an interval of at least 2 hours is needed between administration of orlistat and multivitamins.
  • Vitamin D analogues – an interval of at least 2 hours is needed between administration of orlistat and vitamin D analogues (calcitriol, paricalcitol, cholecalciferol…).

Patients taking warfarin anticoagulants should use orlistat with caution because the reduction of vitamin K absorption in the intestines may increase the anticoagulant effect, increasing the risk of hemorrhage .

As orlistat favors the control of glucose levels, in diabetic patients it may be necessary to adjust the dose of oral antidiabetics so that hypoglycemic episodes do not occur.

Orlistat does not interfere with the effectiveness of the birth control pill.


Orlistat is contraindicated in pregnancy and in patients with severe liver or biliary tract disease. Its use during breast-feeding is also not indicated.

In people with intestinal malabsorption syndrome, the use of orlistat may worsen the condition, so it is contraindicated.