Orlistat

What is orlistat?

Orlistat is a medicine which can help you to lose weight if you have overweight or obesity. Orlistat works by blocking chemicals (enzymes) in your gut which digest fat. Orlistat stops about a third of the fat that you eat from being digested. The undigested fat is not absorbed into your body and is passed out with your stools (faeces).

Orlistat dosage

The normal dose on prescription is one capsule - 120 mg, three times a day with each meal. 60 mg capsules (Alli®) can also be bought without prescription from a pharmacy (see below) - again, the recommended dose is one capsule with each meal, up to three times a day. However, you do not need to take one if there is no fat in the meal or if you miss a meal.

Other weight loss medicines

Other medicines used for weight loss include liraglutide (Saxenda®), tirzepatide (Mounjaro®) and semaglutide (Wegovy®). These were originally developed to treat type 2 diabetes, but are increasingly used for weight loss treatment as well.

The UK's National Institute for Health and Care Excellence (NICE) recommends that these are only used by specialist weight management clinics, for people who have obesity, pre-diabetes, a high risk of developing heart disease (eg having high cholesterol), and alongside a low-calorie diet and increased exercise, for a maximum of two years. They are therefore usually only offered on the NHS for people who meet those criteria, although they are widely available privately.

Two other medicines - sibutramine and rimonabant - previously used to help with weight loss are no longer available in the UK because of concerns over their safety.

How does orlistat work?

Orlistat works by interfering with the way fat is digested and absorbed into the body. Doctors have guidelines as to when orlistat can be prescribed. You can also buy orlistat from pharmacies - but certain conditions apply, detailed below.

If you take orlistat, it may possibly interfere with the absorption of some vitamins, so you should take a multivitamin supplement. Take this at least two hours before, or two hours after taking orlistat. Tell your doctor or pharmacist if you take any other medicines, as orlistat can interfere with the absorption of some medicines.

Doctors usually calculate whether you are underweight, in the 'ideal' weight range, overweight or obese based on your BMI, or body mass index. You can work out your BMI from our BMI calculator.

One way to help with weight loss is to reduce the amount of fat in your diet. See the separate leaflet called Weight reduction.

What special dietary instructions should I follow while taking orlistat?

It is recommended that you reduce your fat intake to 30% of your total calorie intake whilst taking orlistat. Orlistat reduces how much fat gets absorbed from the gut. Fat that isn't absorbed comes out in poo.

So, eating a high-fat diet alongside taking orlistat can worsen side-effects such as flatulence (farting), fatty or oily poo, oily spotting on underwear, increased number of bowel movements, needing to use the toilet suddenly, and loose stools..

Tips on how to reduce your fat intake

• Change from butter or regular spreads to a low-fat spread.

• Choose lean cuts of meat and trim visible fat. Avoid skin on chicken and crackling on pork.

• Avoid added fat/oil when cooking - grill, poach, bake or microwave instead.

• Choose low-fat dairy foods such as semi-skimmed or skimmed milk, low-calorie yoghurts, reduced-fat cheeses and low-fat spreads.

• Choose lower-fat cook-in sauces with less than 5 g fat per 100 g sauce.

Does orlistat work?

Studies have shown that, on average, orlistat, plus a weight-reducing diet and exercise, causes more weight loss than a weight-reducing diet and exercise alone. Some people lose 10% or more of their body weight within six months with the help of orlistat. In others, it is less effective.

One reason why orlistat may not work is that you may think that you can relax your weight-reducing diet, and the orlistat will 'do it all'. This is not true. In order to lose weight you still have to eat less and exercise regularly.

Remember, orlistat prevents only some of the fat that you eat from being absorbed (just under a third). But, if you do not keep to a healthy weight-reducing diet, and you eat more fat or sugar (chocolates, cakes, etc), the extra fat that you eat will easily cancel out the effect of the orlistat.

Who can use orlistat?

Orlistat isn't suitable for everyone who wants to lose weight. It is only recommended in people over a certain body mass index (BMI). Doctors should ensure that changes to eating and exercise habits have been tried first for weight loss, and should only use orlistat alongside these, and not on its own.

Doctors are expected to use the following guidelines when prescribing orlistat:

• Your BMI:

  • Must be 30 or above; or

  • Must be 28 or above, and you have a medical condition that would benefit from losing weight (such as diabetes or high blood pressure).

• The goal is a 5% (or more) weight loss within three months of starting orlistat. If this hasn't happened, orlistat is unlikely to be an effective treatment for you, and should be stopped.

How long does orlistat take to work?

As long as orlistat has successfully helped in reducing weight by 5% or more after three months, there's no restriction on how long it can be used for. However, it should be regularly reviewed with your doctor. If the side-effects are becoming difficult to manage, or if it's no longer working (for example, your weight is static or increasing), then it may be time to stop.

Keeping to a reduced weight

After treatment is stopped, a number of people who have lost weight with the help of orlistat put weight back on. Try to anticipate this. Once you have lost some weight, you are more likely to keep your weight down if you stick to a healthy diet, exercise regularly (if you are able) and weigh yourself once a week.

See the separate leaflet called Obesity and weight loss for more details.

Can I buy orlistat?

In the UK orlistat 120 mg is available on prescription from your doctor or as a private (paid for) service from some pharmacies through Patient Access. Low-dose orlistat (60 mg) is also available to buy over the counter in pharmacies, based on pharmacists' clinical judgement. Pharmacists are also expected to follow guidelines when giving orlistat, which include:

• Your BMI must be 28 or above.

• Your BMI should be checked on each occasion that you request orlistat.

• You must be over the age of 18 years.

• You should not take orlistat for more than six months over the counter (at the 60 mg dose).

• If you have not lost at least 5% of your weight after taking orlistat for three months, you should not continue to take it.

Your pharmacist will also give you advice on an appropriate diet - a low-fat and reduced calorie diet.

Orlistat side-effects

The common side-effects of orlistat are caused by the fat which is passed out with your stools (faeces). You may have fatty smelly stools, urgency to get to the toilet, oily spotting on your underwear, and excess wind.

These side-effects are less likely if you eat a low-fat diet. They tend to settle with time, possibly because if they occur they remind you that you should be eating a low-fat diet. Other side-effects are rare.

Note: the above is not the full list of side-effects for those taking orlistat. Please see the leaflet that comes with your medicine for a full list of possible side-effects and cautions.

Who should not take orlistat?

The following people should not take orlistat:

• Pregnant or breastfeeding women.

• People under the age of 18 years.

• People who have a condition where food is not absorbed properly (a malabsorption syndrome).

• People with cholestasis. This is a condition where bile does not flow properly from the liver to the duodenum.

Orlistat can also interfere with the absorption of various medicines and vitamins and affect the way that they work. For example, orlistat interferes with:

• Some treatments for HIV and AIDS.

• Ciclosporin.

• Acarbose.

• Levothyroxine.

• Amiodarone.

• Warfarin.

• Some treatments for epilepsy.

It may also affect how well contraceptive pills work if you have so much diarrhoea that they don't absorb properly. If you take orlistat:

• If you take the contraceptive pill and have severe diarrhoea you should use other methods of contraception in addition to the pill - for example, condoms.

• Tell your doctor or pharmacist about other medicines that you take, before starting on orlistat.

• Take a multivitamin supplement at least two hours before, or two hours after, taking orlistat - to help ensure adequate vitamin intake. Some people find it easiest to take this at bedtime.

Always read the packet leaflet for a full list of cautions and of people who should not take orlistat.