The American Food and Drug Administration (FDA) has approved Orlistat for use as an over-the-counter weight loss drug for adults who are overweight. The drug, which was originally approved for prescription in 1999, will retain prescription status at higher doses for the medical treatment of obesity.

The FDA said that the drug on its own will not work. If you are overweight and use the drug to lose weight you need to be on a "reduced-calorie, low-fat diet, and exercise program," they said.

Dr. Douglas Throckmorton, Deputy Director at the FDA's Center for Drug Evaluation and Research said yesterday, "We know that being overweight has many adverse consequences, including an increase in the risk of heart disease and type 2 diabetes." He said that this over the counter drug, along with "diet and exercise, may aid overweight adults who seek to lose excess weight to improve their health."

Orlistat will be manufactured by GlaxoSmithKline as the brand Alli and will be available for adults over 18 years of age in 60 mg capsule form to be taken up to 3 times a day with meals that contain fat.

The drug works by reducing your gut's ability to absorb fat. Since this could also reduce the absorption of essential nutrients, if you take the drug you should also take a multivitamin supplement before going to bed, the FDA said.

There are contra-indications. You should not take Orlistat if you are not overweight or if you cannot absorb food properly, according to the FDA.

The National Institutes of Health define overweight as having a Body Mass Index (BMI) of 27 kg per metre squared. This is a figure where you divide your weight in kilogrammes by the square of your height in metres.

The FDA warn that if you have had an organ transplant you should not take the over the counter Orlistat because it could interfere with your other drugs. Also, if you are on blood thinners, or are receiving treatment for diabetes or thyroid disease you should talk with your doctor about whether this drug is right for you.

The side effects of over the counter Orlistat include disruption to bowel habits, such as looser stools. This effect can be reduced if you are on a low fat diet.

Orlistat is a reduced strength version of Xenical (manufactured by Roche) which is available under prescription for the treatment of obesity. It is normally prescribed by doctors in conjunction with a calorie controlled diet.

Orlistat is also known as tetrahydrolipstatin, and works by slowing down the release of lipase, a pancreatic enzyme that breaks down fatty triglycerides in the gut. Inhibition of lipase release means that a proportion of triglycerides do not get converted into fatty acids that would normally be absorbed into the bloodstream. Instead they pass through the gut into the feces, which is why this can cause looser stools.

In the prescription dose of 120 mg three times a day the drug prevents about 30 per cent of fat in the food from being absorbed.

This is the first time the FDA has approved a weight loss drug for over the counter use.

Written by: Catharine Paddock