GPs accused of ignoring obesity drug side effects

The treatments - which are prescribed up to a million times a year - have been linked to increased blood pressure and diarrhoea.

The side effects can be even worse if the drugs are not combined with a low-fat diet.

Prescriptions for the two main anti- obesity medicines, orlistat and sibutramine - marketed as Xenical and Reductil - have soared in recent years.

Annual orlistat prescriptions rose from 17,800 to 646,700 between 1998 and 2005 - a 36-fold increase.

Sibutramine prescriptions have risen four-fold from 2001 to reach 227,000 a year.

LibDem health spokesman Norman Lamb claimed the figures showed ministers had failed to tackle the root causes of obesity.

"The NHS is spending more on costly and potentially dangerous drugs while slashing public health spending simply to make ends meet," he said. "Drugs also do little for the ticking time bomb of childhood obesity, which needs good exercise habits and a culture of healthy eating.

"If the Government doesn't tackle these fundamental issues, over half the nation's children will be obese by 2020."

A spokesman for the British Dietetic Association said: "These drugs can have serious side effects, such as uncontrollable diarrhoea and serious high blood pressure affecting the heart and lungs.

"Doctors should be encouraging people to look at their lifestyles more and take responsibility for what they are eating."

The National Institute for Health and Clinical Excellence has ruled that doctors should only prescribe the drugs if a patient is either obese or very overweight with associated health problems.

The rationing watchdog also said patients must first lose some weight through lifestyle changes or at least try to do so.

There are concerns, however, that GPs are not sticking to the guidelines. In 1998, they spent just £20,000 on anti-obesity drugs but by 2005 the annual cost had risen to more than £38million.

Researchers from Imperial College in London, who obtained the figures, said it was hard to explain the increase in prescriptions.

Colin Waine, chairman of the National Obesity Forum, warned that the pills were not magic bullets. "You have to make lifestyle changes, such as eating more healthily and exercising more, for them to work," he said.

"But the drugs do help you to sustain these changes. They should not be used to get rid of minor excesses of body fat. They are not designed to get you from a size 14 to a size 12."