Perhaps one of the most frequently posed questions regarding weight loss products is:

  • How does it work?

The answer:

  • It depends on the product.

And when it comes to weight loss, there are several avilable and these work in a variety of different ways.

For example, weight loss supplements which you can buy over the counter are very different to weight loss pills; and use a different mechanism to help the user lose pounds. Some of these may (or at least claim to) reduce the appetite of the user or increase the rate at which the body burns calories.

Weight loss medicines containing orlistat, such as Xenical and of course generic Orlistat, can only be obtained on prescription after consultation with a doctor; and Alli, while not a prescription medicine, also requires assessment by a pharmacist prior to issue and use. These help the user lose weight in a different way than supplements and appetite suppressants do.

What Orlistat does in the body

Most medicines work by being uptaken into the bloodstream, but orlistat is different. This particular treatment performs its function in the gut.

Orlistat is a type of drug called a lipase inhibitor. The way these work is by preventing the action of enzymes produced by the pancreas and gastrointestinal tract, called lipases.

Normally, lipases extract fat from the food we eat and absorb them into the blood. Following this, fat is either converted into energy or stored by the body.

Orlistat prevents this from happening by inhibiting lipase function, thus preventing fats from being taken up into the blood. Instead, they are excreted through feces.

It is taken just before, at the same time as or very shortly after (up to one hour) eating a meal, thus working on the prevention of fats taken up from that meal (so if a person consumes a meal which does not contain any fat, they do not need to take the medicine).

It does not completely block or prevent all fat uptake; it only stops around 30 per cent of fats being absorbed. However, this is enough to drastically reduce the calorie and fat intake from someone who has a BMI of 27 or above.

One study assessing the efficacy of orlistat found that it helped users lose an average of just under one kilo per month for the first four months of use.

What about other weight loss pills?

As of September 2015, Orlistat (which is also marketed under the brand name Xenical) is the only licensed prescription medicine available in the UK for weight loss.

While there are several non-prescription supplements and slimming aids available in high street pharmacies, no other weight loss ‘medicine’ is legally available in the UK.

For this reason buying diet pills online should be approached with caution. If a website claims to be selling prescription weight loss medication which is not Xenical or Orlistat, then it is likely not a safe treatment.

As these medicines are not subject to regulated manufacturing standards and clinical testing, it is impossible to know how they will work in the body and, consequently, the risk to health they may pose.

You can find out more about how to buy weight loss treatment online safely on our information page.

Page last reviewed:  05/10/2020