Does Orlistat work?

Woman who has lost weight wearing jeans that no longer fit her and pulling them to show the extra space around the waistline
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Orlistat is a medical treatment designed to help obese individuals lose weight. It works by preventing the absorption of fat from the diet and is intended for use with a calorie-reduced diet. It is available on prescription, however, a lower strength called Alli is available to buy over the counter. Alli is only available to buy after you have had a consultation with a pharmacist, and they think that it is clinically suitable for you to use. Your BMI needs to be above 28 in order to qualify for treatment.


How does Orlistat work?

Usually, dietary fat is broken down by enzymes in the digestive system and stored in the body. Orlistat blocks enzymes from breaking down fat, which means it cannot be stored in the body. Instead, 30-40% less fat is absorbed, which is then expelled from the body in the form of faeces.


Does Orlistat work?

One clinical trial studying the effects of orlistat on weight loss in 743 overweight patients, found that after the first year, those taking orlistat had lost on average 10.3kg of weight.
Another clinical trial has looked at the effects of Orlistat over a 6-month period in 80 obese individuals. After 6 months, Orlistat had caused a 4.65kg reduction in weight, a 1.91kg/m2 reduction in BMI, a 4.84cm reduction in waist circumference, as well as a reduction in cholesterol levels.
So yes, clinical trials and research suggest that Orlistat is an effective method in reducing weight. For optimum results, it is important to use orlistat in conjunction with a calorie reduced diet and an exercise plan. During clinical trials, orlistat has also shown to have a positive impact on blood pressure, cholesterol and diabetes.​


How much weight will I lose with Orlistat?

Extensive research has demonstrated that Orlistat is effective for weight loss. However, whilst Orlistat is clinically proven to help lose weight, it is difficult to predict exactly how much weight will be lost. In theory, during the clinical trials, those that took orlistat compared to those that didn’t, lost on average around 50% more weight. This implicates that if you were to lose 8kg without orlistat, you would lose 12kg whilst taking it. However, this is theoretical. Everybody is different and we all respond to treatment and lifestyle changes in different ways. It is important to note that weight loss occurs where there is a calorie deficit. Orlistat helps to reduce the absorption of fat, which means your body will be consuming less calories. By following a calorie-reduced diet, you can expect to see the positive results that Orlistat has on weight loss. Exercising regularly will also help to achieve a calorie deficit, as many of the calories consumed, will be burnt and used up as energy supplies whilst exercising. Much of the weight loss process lies with how much effort you are willing to put in, with regards to following a disciplined eating and exercise regime. Orlistat blocks the absorption of 30-40% fat consumed from your diet and whilst it is difficult to predict how much weight you will lose with Orlistat, if you are able to put into practice a healthy lifestyle, in almost all cases, Orlistat will exert its beneficial effect.


How do I take Orlistat?

Take one Orlistat capsule just before, during, or no later than one hour after your main meals (breakfast, lunch and dinner). Each capsule should be swallowed whole with water. Please note that if a meal has no fat, an orlistat capsule is not required. Snacks that contain fat should be avoided in-between meals.

Your daily fat intake should not exceed 30% of your daily calorie intake. For example, if you consume 1,600 calories a day, a maximum of 480 calories (which is 30% of 1,600 calories) can come from fat. It is advisable to look at the nutritional content information that is available on most food packaging to help you.​


What are the side-effects of Orlistat?

As with all medication, some people may experience side-effects when taking orlistat. Most side-effects generally pass after a week or so, once your body has gotten used to orlistat. Common side-effects of orlistat include:

  • ​Fatty or oily stools
  • Passing stools more often
  • Oily spotting on underwear
  • Passing wind more often
  • Stomach aches
  • Headaches

Orlistat works by reducing the amount of fat your body absorbs. The fat that is not absorbed leaves your body in the form of faeces. Most of the above side-effects are much less likely to occur if you stick to a low-fat diet.
Women taking the contraceptive pill and orlistat must follow the advice for a missed pill if they experience diarrhoea whilst taking orlistat.


Why do I need vitamins with Orlistat?

​When using orlistat, it is advised to take Vitamins A, D, E and K. These are known as fat-soluble vitamins. Orlistat blocks the absorption of fat in the body, which can impact the amount of fat-soluble vitamins that your body receives. Taking a multi vitamin that contains vitamins A, D, E and K is therefore advisable.

Whilst all of our content is written and reviewed by healthcare professionals, it is not intended to be substituted for or used as medical advice. If you have any questions or concerns about your health, please speak to your doctor.