Rimonabant, also known as Acomplia, is the first drug to target a natural body system that governs a host of factors controlling appetite, weight, metabolism and energy use.

Research suggests that it has the capacity to combat a smoker’s craving for nicotine.

Britain is the first country to receive Rimonabant, after the decision by drug regulators last week to grant it a licence throughout the European Union. Experts say that 20 per cent of Britain’s population could be eligible for treatment.

However, the drug is unlikely to be widely available until it is approved by the National Institute for Health and Clinical Excellence.

The institute, which advises on NHS best practice, is not expected to issue guidance on Rimonabant for two years.

At a cost of £55.20 per patient per month, or £1.97 per tablet, even treating a fraction of the group eligible could cost the NHS billions.

The drug’s manufacturers, Sanofi Aventis, argues that the drug represents good value for money when set against the £7 billion-per-year cost of tackling the problems connected with obesity and being overweight.

Anthony Barnett, a diabetes specialist from the University of Birmingham who took part in yesterday’s launch at the Science Museum in West London, said that it would be a “great shame” if use of the drug was limited by funding issues.

“The real question is, can we afford not to treat?” he said.

In a series of trials involving more than 6,000 patients in America and Europe, about a quarter of those taking Rimonabant lost more than 10 per cent of their initial body weight after a year. About a half lost more than 5 per cent of body weight. Waist circumference, seen by many experts as a more important measurement, was reduced by between six and seven centimetres.

Significant improvements in measures of glucose control, cholesterol and triglyceride blood fats were also seen. These went far beyond what might be expected simply by losing weight. For example, levels of high-density lipoprotein “good” cholesterol, which reduce heart disease risk, showed an 8 to 9 per cent increase, but only half of this was because of weight loss.

There is also trial data suggesting that the drug can help people to give up smoking by overcoming their cravings. However, it is being marketed only to tackle obesity.

Rimonabant is licensed for the treatment of obese patients, or overweight patients with associated risk factors such as type 2 diabetes or poor cholesterol and triglyceride readings.

Experts agree that such treatments are urgently needed as Britain’s obesity rates spiral upwards. One in five adults in the UK — almost 10 million people — is clinically obese.

Obesity is defined as having a body mass index (BMI) of 30 or more. The figure relates weight and height. A person who is overweight has a BMI of 25-30, and someone of normal weight between 18.5 and 24.9.

Professor Barnett said that obesity rates in Britain were climbing faster than anywhere else in the world. The proportion of obese people was expected to overtake that in the United States in 20 years.

David Haslam, a GP and clinical director of the National Obesity Forum, said that therapies such as Rimonabant were a “real step forward”. Other anti-obesity medications are available, but it is the only one to target the endocannabinoid system, which is involved in the regulation of appetite.

Rimonabant works by blocking molecular receptors that, when activated, trigger a cascade of biological events affecting food intake and energy use, as well as fat and glucose metabolism.

“Preventative measures are not enough. Priority should be given to treatment as well as prevention,” said Dr Haslam, a GP from Hertfordshire.

“The launch of Rimonabant is important news for patients who are overweight, with type 2 diabetes, or low HDL cholesterol or high triglycerides. These patients are at high risk of developing heart disease.” Rimonabant is scheduled to be launched later this year in Denmark, the Irish Republic, Germany, Finland and Norway.

Sanofi is still awaiting US marketing approval, which it has said could come by the end of this year. American health authorities have requested more information on the drug.

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