Lose weight with Orlistat in an effective and safe way

Orlistat (generic Xenical) is a weight-loss medicine commonly prescribed to patients struggling with obesity. Alongside a healthy, low-fat diet and exercise programme, orlistat can help you lose weight effectively.

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Virginia Chachati

Reviewed by Virginia Chachati MPharm
(2013, University College London)
GPhC Registration number: 2087654

Information last reviewed 06/04/21


What is Orlistat?

Orlistat (generic Xenical) is a type of weight-loss medicine that is prescribed to patients struggling with obesity. Taking orlistat in combination with a low-fat diet and regular exercise can help you lose weight effectively.

How does Orlistat work?

Orlistat is not absorbed into the bloodstream, but works locally in the stomach and small intestine by preventing an enzyme, called lipase, from digesting fat. As a result, you cannot absorb at least a third of the fat you eat. This fat will be passed out of your body with your stools. You will lose weight if you follow a calorie-reduced low-fat diet and exercise regularly alongside taking orlistat.

How long does it take for Orlistat to work?

Orlistat can help you start losing weight within two weeks. However, if you have not lost at least 5 % of your body weight within the first three months of treatment, you should see your doctor. They may discuss your treatment plan and alternative weight-loss methods.

How will I know if Orlistat has started working?

Orlistat will help you lose weight when accompanied by a low-fat diet and regular exercise. You may want to weigh yourself weekly to see if there are any changes in your body weight. Orlistat should start working within two weeks. However, orlistat only works in the presence of dietary fat in your body, so if you cut fat out of your diet altogether, this treatment will have no effect. Keep in mind that you must eat fat in your diet to help you absorb essential vitamins such as vitamins A, D, E and K. Eating a balanced, healthy diet, as recommended by a doctor or dietitian, is the safest and most effective way of losing weight while using orlistat.

How effective is Orlistat?

Orlistat is effective after two weeks of use and you should see your body weight reduce by a minimum of 5 % after three months. The effectiveness of Orlistat differs from patient to patient. Results are reliant on dietary changes and whether the patient is following an exercise programme. Orlistat is the only weight-loss medicine proven to be safe and effective for use in the UK.

What to do if someone has an eating disorder and is taking Orlistat?

Orlistat is prescribed to patients who are struggling with obesity and have failed to lose weight using other methods. Orlistat should never be used by someone who is of a healthy weight or underweight and is trying to lose more weight. If you suspect that someone you know is struggling with an eating disorder, try letting them know that you are worried about them and suggest that they speak to a healthcare professional. This can be difficult, as people suffering from eating disorders may not be willing to accept help. Visit the NHS website for advice on how to help if someone you know has an eating disorder.


Active ingredients

The active ingredient in Orlistat is orlistat 120 mg.

Inactive ingredients

The inactive ingredients in Orlistat are cellulose microcrystalline PH 112, sodium starch glycolate (type A), silica, colloidal anhydrous, sodium laurilsulfate, gelatine, titanium dioxide (E171) and indigo carmine (E132).

Please Note: Generic Orlistat is made by a range of different manufacturers and may contain different ingredients than those listed above. Please check the patient information leaflet provided for further details.

Which ingredients can cause an allergic reaction?

While a very serious allergic reaction to this drug is rare, it is important to look out for the signs of an allergic reaction when taking this medication for the first time. Hives/rash, swelling of the face/lips/tongue, difficulty breathing, dizziness and chest tightness are signs of an allergic reaction. Get medical help right away if you notice any symptoms and stop taking the medication immediately. Do make sure to let your prescribing doctor know.


How to take Orlistat?

Always take Orlistat as instructed by your doctor. Take orlistat in combination with a well-balanced calorie-controlled diet that contains plenty of fruits and vegetables and contains roughly 30% of calories from fat. You should also try to distribute your daily intake of fat, carbohydrate and protein evenly across your three daily meals. Swallow one orlistat 120 mg capsule with water immediately before, during or within an hour of each meal. For best results, avoid eating fat-containing foods between meals, such as biscuits, chocolates and crisps. 

If you miss a meal, or have a fat-free meal, you do not need to take an orlistat capsule. If you forget to take an orlistat capsule, try and remember to take it within an hour of your last meal. If an hour has already passed, just skip the dose and take your next one as planned with your next meal. Never take a double dose to make up for a missed one.

Orlistat dosage

Your doctor or pharmacist will decide the dose of orlistat that is right for you. The usual dose is one orlistat 120 mg capsule with each of your three main meals per day.

When can I stop taking Orlistat?

When starting treatment with orlistat, you take it for three months and stop if your body weight has not reduced by at least 5 %. Otherwise, orlistat can be continued for 12 months or longer if advised by your doctor. Always take orlistat as prescribed by your doctor. 

How to stop taking Orlistat?

After stopping treatment with orlistat, you should stick to a healthy, balanced diet and exercise regularly to avoid putting weight back on. If you have not lost at least 5 % of your body weight within three months, your doctor will review your treatment.

Do I need to change my diet when taking Orlistat?

Before taking orlistat, your doctor will recommend a healthy diet that is low in fat and regular exercise. You should begin this diet and exercise regime prior to treatment, for the duration and after you finish taking orlistat. Orlistat works best with a calorie-reduced and low-fat diet.

Side Effects

Orlistat side effects

Like all medicines, orlistat can cause side effects in some patients. If you feel unwell while taking orlistat, tell your doctor or pharmacist as soon as possible.

The following side effects can occur in more than 1 in every 10 patients:

  • Headache
  • Abdominal pain or discomfort
  • Diarrhoea
  • Flatulence with discharge
  • Oily discharge
  • Oily or fatty stools
  • Low blood sugar levels
  • Upper respiratory tract infections
  • Flu-like symptoms

Common side effects (affecting 1 to 10 in 100 patients) include:

  • Rectal pain or discomfort
  • Soft stools
  • Incontinence
  • Bloating
  • Tooth or gum disorders
  • Irregularity of menstrual cycle
  • Tiredness
  • Anxiety
  • Lower respiratory tract infections
  • Urinary tract infections

The following side effects have been reported, although it is unknown how common they are:

  • Allergic reaction (rash, itching, difficulty breathing, nausea, vomiting, and feeling of being unwell). You should contact your doctor immediately if you experience any of these symptoms
  • Skin blistering
  • Diverticulitis
  • Bleeding from the rectum
  • Increased level of liver enzymes found in blood test
  • Hepatitis (yellowing of the skin or whites of the eyes, itchy skin, dark coloured urine, stomach pain, liver tenderness, loss of appetite)
  • Gallstones
  • Pancreatitis
  • Oxalate nephropathy
  • Effects on clotting with anticoagulants


You should NOT take Orlistat if:

  • You are allergic to any of the ingredients in this medicine
  • You have chronic malabsorption syndrome (reduced ability to absorb nutrients from the gastrointestinal tract)
  • You have cholestasis
  • You are breastfeeding

Take extra care when using orlistat if:

  • You eat a meal that is high in fat while taking orlistat. Gastrointestinal side effects are likely to increase if orlistat is taken with a high-fat meal.
  • You regularly take an oral contraceptive. Possible failure of your contraceptive may occur if you experience severe diarrhoea while taking orlistat, so you are recommended to use additional contraceptive methods such as condoms.
  • Inform your doctor if you suffer from kidney problems, as orlistat can be associated with renal stones in patients with chronic kidney disease.

Drug interactions

Before taking orlistat, let your doctor or pharmacist know if you are taking any other medicines, including those purchased over the counter at a pharmacy without a prescription. Remember that weight loss may lead to the dose of your other medicines being changed. Important medicines you should let them know about include:

  • Anticoagulants, such as warfarin
  • Ciclosporin
  • Iodine salts or levothyroxine
  • Amiodarone
  • Medicines used to treat HIV
  • Medicines for depression, psychiatric disorders or anxiousness
  • Medicines used to treat epilepsy
  • Acarbose (used to treat type 2 diabetes)

How to minimise side effects of Orlistat?

Orlistat is not absorbed by the body, but works locally in the stomach and small intestine to block a third of fat digestion. Therefore, you may experience side effects such as abdominal cramps with oily stools or diarrhoea. This is because your body is getting rid of roughly a third of the fat you are eating, so the best way to avoid these side effects is to maintain a low-fat diet, eat smaller portions and limit yourself to three meals a day without fatty snacks. Your meals will include wholegrains, fruits and vegetables, low fat dairy products and lean cuts of meat.

Orlistat and alcohol

Avoid drinking alcohol immediately after taking a dose of orlistat as the effects of alcohol on your body can be prolonged. This is because orlistat reduces how quickly you can break down alcohol, making you more likely to feel drowsy or intoxicated after drinking.

Treatment Options

Orlistat vs Xenical

Orlistat is the generic name of the medicine, which is also available under the brand name Xenical. Both orlistat and Xenical contain the same amount of the active ingredient, orlistat 120 mg, and work in exactly the same way, but Xenical is slightly more expensive.

Orlistat vs over the counter weight loss treatments

While Orlistat (Xenical) is the only proven effective and safe weight-loss medicine, there are many products available over the counter which claim to help you lose weight. Alli is a prescription-free treatment that contains a lower dose of orlistat (60 mg) and can be purchased over the counter under the supervision of a pharmacist. However, other slimming products lack clinical evidence to suggest they are effective. Avoid any product that claims to be a ‘quick fix’, as losing weight too quickly can be dangerous. If you feel you would like to lose some weight, make small long-term changes to your lifestyle. No weight-loss product will help you to lose weight if you maintain a high calorie diet. Always seek advice from a healthcare professional before following an exercise routine or going on any strict diets.

Can I use other weight loss treatments with Orlistat?

Orlistat is the only weight-loss treatment that can be recommended by doctors. You can use meal replacement products to help with weight loss to maintain a calorie-reduced low-fat diet while using orlistat. Using other weight loss treatments may not be suitable to use alongside orlistat depending on your weight loss goals.


Is Orlistat an appetite suppressant?

Orlistat is not an appetite suppressant. Orlistat works by limiting your body’s absorption of fat through blocking fat-digesting enzymes directly.

Do I need to exercise when taking Orlistat?

Exercising regularly helps accelerate and maintain weight loss. You should begin exercising before taking orlistat, and continue throughout your treatment course.

Will Orlistat affect my period?

Orlistat works by blocking a third of your body’s absorption of fat. If your period is irregular, delayed, or stops altogether, it may mean that your body is not absorbing enough necessary fats or nutrients and treatment may need to be discontinued. If you are worried about disruptions to your menstrual cycle while taking Orlistat, speak to your doctor for advice.

Can I take Orlistat to prepare for surgery?

Orlistat can be prescribed in preparation for surgery, as surgeons will often not operate unless a patient is below a certain weight. Surgery is generally a last resort treatment for obesity and only becomes an option when you have tried other weight-loss methods.

Can I take Orlistat after weight loss surgery?

Orlistat can be taken following surgery, but only if recommended by a doctor. Orlistat can be prescribed following liposuction to help you keep off the weight you have lost, but is unlikely to be prescribed to patients who have had a gastric band fitted.

How much weight could I lose on Orlistat?

The amount of weight you can lose with orlistat depends on your starting weight and whether you follow a low-fat calorie-reduced diet and regular exercise programme. The initial weight-loss aim is 5 % of your overall body weight within the first three months.

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