It is a fat absorption medicine, not a direct fat burner. Orlistat is intended to be used alongside a reduced-calorie diet and physical activity, with realistic expectations about weight loss.
What is Orlistat?
Orlistat is a drug for weight loss. It is part of a group of medicines called lipase inhibitors and works mainly in the digestive tract.
Its action targets enzymes responsible for digesting dietary fat. By reducing their activity, orlistat decreases the amount of fat that can be broken down and absorbed.
Orlistat is available in the UK in different strengths and formulations. BMI, health risks, medical history and other medicines being taken will determine the right product and if treatment is suitable.
How does Orlistat work?
Orlistat works by blocking gastric and pancreatic lipases. These enzymes normally break down dietary fat into smaller pieces that can be absorbed through the intestine.
When orlistat inhibits these enzymes, some of the fat eaten with a meal is not broken down or absorbed normally. Instead, the undigested fat passes through the digestive tract and is eliminated in the stool.
This means orlistat reduces the amount of dietary fat entering the body; it does not directly stimulate the body to burn stored fat.
The same mechanism also explains many of its characteristic gastrointestinal effects. More unabsorbed fat remaining in the bowel can lead to oily stools, urgency and other changes in bowel habits.
Does orlistat block all dietary fat?
No. Orlistat does not prevent all dietary fat from being absorbed. It reduces the amount that is digested and absorbed, while some fat continues to be absorbed normally.
For this reason, orlistat should not be viewed as a way to offset a high-fat diet. A balanced, reduced-calorie diet remains an important part of treatment.
What are the uses of Orlistat?
The main use of Orlistator is within weight management for people who meet appropriate clinical criteria.
NICE recommends considering orlistat alongside lifestyle measures for adults with a BMI of 30 kg/m² or more, or 28 kg/m² or more where weight-related risk factors are present.
Orlistat is not intended to replace dietary changes, physical activity or behavioural support. A healthcare professional should also consider whether the medicine is appropriate based on the person's health, existing medicines and potential contraindications.
What diet should you follow with Orlistat?
Orlistat is intended to be used with a balanced, calorie-controlled diet rather than a high-fat eating pattern.
This is particularly important because eating more fat can leave more unabsorbed fat in the digestive tract, increasing the likelihood of oily stools, urgency, diarrhoea and other gastrointestinal effects.
The aim is not to eliminate dietary fat completely. Fat provides energy and essential fatty acids and helps the body absorb fat-soluble vitamins. Instead, overall fat intake should be appropriate for the person's weight-management plan.
What are the common side effects of Orlistat?
The most characteristic Orlistat side effects affect the digestive system because of the medicine's effect on dietary-fat absorption.
They can include:
- Oily or fatty stools
- Oily rectal discharge
- An urgent need to open the bowels
- More frequent bowel movements
- Flatulence, sometimes with discharge
- Abdominal discomfort
- Diarrhoea
These effects are particularly associated with meals containing larger amounts of fat. Following the dietary recommendations provided with treatment can help reduce their frequency.
Gastrointestinal effects are generally the most noticeable adverse effects of orlistat. Speak to a doctor or pharmacist if symptoms are persistent, severe or difficult to manage.
Can Orlistat affect vitamin absorption?
Yes. Because Orlistat reduces dietary-fat absorption, it can also reduce absorption of the fat-soluble vitamins A, D, E and K.
UK product information recommends a multivitamin supplement during orlistat treatment to help maintain adequate vitamin intake. Where a multivitamin is used, it should be taken separately from orlistat, generally at bedtime.
This is an important part of understanding how orlistat works: its effect is not limited to calories from dietary fat, so nutritional intake also needs to be considered during treatment.
Who may be suitable for Orlistat?
NICE identifies orlistat as a weight-management option for adults with a BMI of 30 kg/m² or above, or 28 kg/m² or above, where associated risk factors are present.
However, meeting a BMI threshold does not automatically mean that orlistat is suitable.
A healthcare professional should consider medical history, current medicines, possible contraindications and whether the person can follow the dietary and lifestyle measures recommended alongside treatment.
When should Orlistat not be used?
Orlistat is not suitable for everyone. UK product information lists contraindications, including chronic malabsorption syndrome, cholestasis and hypersensitivity to orlistat or its ingredients.
Pregnancy and breastfeeding are also listed as situations in which orlistat should not be used in the relevant product information.
There are also important medicine-related contraindications and precautions, including interactions involving ciclosporin and oral anticoagulants such as warfarin.
Anyone with an existing medical condition or taking regular medicines should speak to a doctor or pharmacist before starting Orlistat.
Can Orlistat interact with other medicines?
Yes. Orlistat can affect the absorption or effectiveness of certain medicines.
Important examples include:
- Ciclosporin: Orlistat can reduce ciclosporin levels.
- Warfarin and other oral anticoagulants: anticoagulant control may be affected.
- Levothyroxine: absorption and thyroid control may be affected.
- Antiepileptic medicines: changes in absorption may affect seizure control.
- HIV antiretroviral medicines: Orlistat may reduce their absorption.
- Amiodarone: changes in amiodarone levels have been reported.
Orlistat can also affect absorption of fat-soluble vitamins. Tell your doctor or pharmacist about prescription medicines, over-the-counter products, supplements and herbal products before starting treatment.
Does Orlistat guarantee weight loss?
No. Orlistat does not guarantee weight loss and should not be presented as a quick solution.
Its mechanism can reduce the amount of dietary fat absorbed, but the overall effect on body weight also depends on diet, physical activity, adherence and individual circumstances.
NICE recommends using weight-management medicines alongside dietary and lifestyle measures. Treatment should also be reviewed to determine whether it is providing meaningful benefit.
NICE recommends stopping orlistat after 12 weeks if the person has not lost at least 5% of their initial body weight.
This provides a realistic expectation: Orlistat is intended to support a structured weight-management programme rather than replace it.
What happens if you eat a high-fat meal while taking orlistat?
A high-fat meal can make gastrointestinal side effects more noticeable.
Because orlistat prevents some dietary fat from being digested and absorbed, more unabsorbed fat can remain in the bowel. This may cause oily stools, urgency, diarrhoea, abdominal discomfort or oily discharge.
Following the recommended dietary approach can therefore make treatment easier to tolerate.
Is Orlistat a fat burner?
No. Orlistat is not a conventional 'fat burner'.
It does not directly stimulate the body to burn stored fat. Instead, it inhibits digestive enzymes that break down dietary fat, meaning some of the fat consumed with food passes through the digestive system without being absorbed.
This distinction is important because orlistat's effect depends on dietary fat and forms part of a wider weight management treatment, rather than working as a standalone fat-burning medicine.
Frequently asked questions
What is Orlistat used for?
Orlistat is used as part of weight management for eligible adults with overweight or obesity. It reduces dietary-fat absorption alongside diet and physical activity.
How does Orlistat work?
Orlistat inhibits digestive lipases, reducing the breakdown and absorption of dietary fat. Some undigested fat then passes through the digestive system instead.
Does Orlistat block all fat absorption?
No. Orlistat reduces the absorption of some dietary fat but does not block all fat. Some dietary fat can still be digested and absorbed normally.
Who can take Orlistat?
Eligibility depends on factors including BMI and weight-related health risks. NICE identifies relevant BMI thresholds of 30 or 28 with associated risk factors.
What are the main side effects of Orlistat?
The main effects are gastrointestinal, including oily stools, urgency, increased bowel movements, flatulence, abdominal discomfort and diarrhoea, especially after high-fat meals.
Can Orlistat interact with other medicines?
Yes. Orlistat can interact with medicines including ciclosporin, anticoagulants, levothyroxine, antiepileptics and some HIV medicines, making professional advice important.
The bottom line
Orlistat is a fat absorption medicine that works by inhibiting digestive lipases and reducing the amount of dietary fat absorbed. It does not directly burn stored fat or guarantee weight loss.
Its use needs to be considered alongside diet, physical activity, eligibility criteria, gastrointestinal effects, vitamin absorption, contraindications and potential medicine interactions.
For more information about weight-management medicines, visit the PharmNexa weight-loss treatment category.
For information about Orlistat specifically, visit the PharmNexa Orlistat product page.
Medical Disclaimer
This article is for general information and does not replace advice, diagnosis or treatment from a qualified healthcare professional. Speak to a doctor or pharmacist about whether orlistat is suitable for you, particularly if you have existing medical conditions or take other medicines.
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