A single pill that tackles obesity and smoking could become the next pharmaceutical industry blockbuster after scientists revealed its first results yesterday.

Rimonabant, made by the French company Sanofi-Synthelabo, has been shown in two separate American trials to speed weight loss in overweight patients and to double the number of people stopping smoking while preventing subsequent weight gain.

The twin effects of rimonabant on two of the Western world's dominant cravings could give it a crucial advantage over other drugs on the market. Preventing weight gain after giving up smoking would remove one of the greatest disincentives for those trying to kick the habit.

Rimonabant is involved in seven trials in more than 13,000 patients around the world. It works by blocking cannabis receptors in the brain and was discovered after researchers decided to investigate why cannabis smokers developed the "munchies", the fierce appetite that often accompanies smoking of the drug.

First results presented to the American College of Cardiology meeting in New Orleans yesterday showed that among 1,036 overweight patients treated for a year in Canada, those given the highest dose of rimonabant lost an average of 8.6kg (1st 5lb), compared with 2.3kg (5lb) for those on placebos.

In a second trial in 787 heavy smokers treated for 10 weeks in the US, 36 per cent of those given rimonabant had stopped smoking, compared with 20 per cent of those on placebo. Those on the drug, brand name Acomplia, lost half a pound weight on average, while those on placebos gained 2.5lb.

Robert Anthenelli, one of the lead researchers in the second trial from the University of Cincinnati College of Medicine, said: "Since these two studies show that rimonabant treats obesity and related metabolic disorders in overweight and obese patients, and also helps people quit smoking without significant post-cessation weight gain, we may have a very promising new approach for managing two major and preventable risk factors for cardiovascular disease with one and the same drug."

British experts welcomed the results. Ian Campbell, chairman of the National Obesity Forum, described the findings as "very positive" . "To achieve an 8kg weight loss over one year is as good as other medications that are available," he said. "I would look forward to the two-year results because once you have got weight down maintaining weight loss is crucial. If it can prevent weight gain in people who stop smoking that could be its unique selling point."

Professor Martin Jarvis, an expert on smoking at University College London, said: "These are encouraging results. I know people are excited about it. For years everyone has been searching for a drug that is effective in reducing weight and doesn't have nasty side-effects. Lowered weight gain after stopping smoking would be an added bonus. Given how obesity is galloping away it must have a potentially really big market."

Rimonabant is the first of a new class of drugs called selective CB1 blockers which act on the addictive pathway in the brain associated with regulating the body's intake of food and tobacco dependency. Research suggests the drug taps into pathways associated with the pleasure obtained by eating, smoking tobacco or smoking cannabis. CB1 receptors are also found in fat cells and have a role in fat and glucose metabolism.

The drug is expected to be on the market in the UK next year.

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