Orlistat is a medicine which can help you to lose weight if you are overweight or obese.
One way to help with weight loss is to reduce the amount of fat in your diet. See separate leaflet called Weight Loss (Weight Reduction).
Orlistat works by interfering with the way that 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 at bedtime. Tell your doctor or pharmacist if you take any other medicines, as orlistat can interfere with the absorption of some medicines.
What is orlistat?
Orlistat is a medicine which can help you to lose weight if you are overweight or obese. Orlistat works by blocking chemicals (enzymes) in your gut which digest fat. Nearly a third of the fat that you eat is blocked by orlistat. The undigested fat is not absorbed into your body and is passed out with your stools (faeces). The normal dose is one capsule - 120 mg, three times a day with each meal. However, you do not need to take one if there is no fat in the meal or if you miss a meal.
Liraglutide is a new medicine that was licensed for the treatment of obesity in January 2017. There has been limited experience of this treatment, which is only available in injectable form. It is currently mainly being used in specialist centres for people whose obesity has led them to develop other illnesses such as diabetes.
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.
It is recommended that you reduce your fat intake to 30% of your total calorie intake whilst taking orlistat. Reported side-effects of eating too much fat include: flatulence, oily spotting on underwear, increased urgency and loose bowel movements.
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 (chocolates, cakes, etc), the extra fat that you eat will easily cancel out the effect of the orlistat.
When is orlistat prescribed?
Orlistat is not used in everyone who wants to lose weight. It is only recommended in people over a certain BMI. For a doctor to prescribe orlistat, they also need to be sure that you have tried changing your diet and increasing your physical activity levels first.
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).
- You must lose at least 5% of your weight by three months from starting orlistat; if not, treatment should be stopped.
How long does orlistat take to work?
If you have lost 5% of your weight within three months, there is no restriction on how long orlistat may be prescribed. However, most doctors will review treatment regularly and will decide if it is still appropriate for you to carry on taking orlistat. If you continue to lose weight after six months, your doctor may advise that you continue to take orlistat. This may be for up to 1-2 years, or longer if you have a great deal of weight to lose.
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.
Can I buy orlistat?
In the UK orlistat is available on prescription from your doctor (120 mg) and low-dose orlistat (60 mg) is also available to buy over the counter in pharmacies. Pharmacists cannot just sell it to anyone. They are also expected to follow guidelines 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.
- If you have not lost 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-calorie and low-fat diet.
The main side-effects 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 underclothes, 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.
- 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 bedtime - a time when you will not be taking orlistat - to help ensure adequate vitamin intake.
Always read the packet leaflet for a full list of cautions and of people who should not take orlistat.
How to use the Yellow Card Scheme
If you think you have had a side-effect to one of your medicines you can report this on the Yellow Card Scheme. You can do this online at .
The Yellow Card Scheme is used to make pharmacists, doctors and nurses aware of any new side-effects that medicines or any other healthcare products may have caused. If you wish to report a side-effect, you will need to provide basic information about:
- The side-effect.
- The name of the medicine which you think caused it.
- The person who had the side-effect.
- Your contact details as the reporter of the side-effect.
It is helpful if you have your medication - and/or the leaflet that came with it - with you while you fill out the report.
Further reading and references
; Association of all-cause mortality with overweight and obesity using standard body mass index categories: a systematic review and meta-analysis. JAMA. 2013 Jan 2309(1):71-82. doi: 10.1001/jama.2012.113905.
; British Psychological Society, 2011
; Dept of Health, March 2013
; NICE Evidence Summary, June 2017
; Dept of Health, 13 October 2011
; Royal College of Paediatrics and Child Health and Dept of Health.
; Royal College of Paediatrics and Child Health, 2012
; World Health Organization
; Interventions for treating obesity in children. Cochrane Database Syst Rev. 2009 Jan 21(1):CD001872. doi: 10.1002/14651858.CD001872.pub2.
; Bariatric surgery for obesity and metabolic conditions in adults. BMJ. 2014 Aug 27349:g3961. doi: 10.1136/bmj.g3961.
; Surgery for weight loss in adults. Cochrane Database Syst Rev. 2014 Aug 88:CD003641. doi: 10.1002/14651858.CD003641.pub4.
; Review of the key results from the Swedish Obese Subjects (SOS) trial - a prospective controlled intervention study of bariatric surgery. J Intern Med. 2013 Mar273(3):219-34. doi: 10.1111/joim.12012. Epub 2013 Feb 8.
; Adolescent bariatric surgery. Arch Pediatr Adolesc Med. 2012 Aug166(8):757-66. doi: 10.1001/archpediatrics.2012.1011.
; Tackling overweight and obesity: does the public health message match the science? BMC Med. 2013 Feb 1811:41. doi: 10.1186/1741-7015-11-41.
; Overweight, obesity, and mortality from cancer in a prospectively studied cohort of U.S. adults. N Engl J Med. 2003 Apr 24348(17):1625-38.
; MEND - Mytime Active
; (Mind, Exercise, Nutrition ... Do it!)
; Obesity and Management of Weight Loss. N Engl J Med. 2016 Sep 22375(12):1187-9. doi: 10.1056/NEJMclde1515935.
; Effects of orlistat on blood pressure: a systematic review and meta-analysis of 27 randomized controlled clinical trials. J Am Soc Hypertens. 2018 Feb12(2):80-96. doi: 10.1016/j.jash.2017.12.002. Epub 2017 Dec 14.
; Royal College of Paediatrics and Child Health, 2017
I've been on Orilstat for 2 months with no side affects. I haven't changed my diet nor my limited exercises but in the last couple of weeks every stool and water is very red. Is this the 'oily' part...jane lily
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