Obesity pill based on cannabis cuts calorie intake by a third

A new slimming pill based on cannabis-induced food cravings will help people lose weight without the need for exercise or diets.

In clinical trials, volunteers taking the experimental drug taranabant consumed a third fewer calories than those on a dummy placebo pill and lost "significant amounts" of weight within 12 weeks.

A larger trial involving thousands of obese patients in America is now underway. If the drug is confirmed to be safe, it could be approved for use among clinically obese patients in less than two years.

Taranabant is designed to have the opposite effect on the brain as cannabis - a drug that usually triggers food cravings known in slang as "munchies".

When people smoke cannabis, active chemicals in the drug stimulate part of the brain known as cannabinoid receptors, creating the side effects of euphoria, relaxation and hunger pangs.

Taranabant works by blocking these receptors - suppressing appetite and speeding up the body's metabolism.

Dr Steven Heymsfield, of Merck Research Laboratories in New Jersey, America, said: "The effects of marijuana on appetite have been known for millennia from its medicinal and recreational use.

"The ingredient responsible stimulates cannabinoid receptors. When you block the cannabinoid system with an antagonist like taranabant, you suppress appetite."

In a 12-week trial of 533 obese people, those taking the drug lost significantly more weight than people given a useless placebo pill, the researchers report in the journal Cell Metabolism.

Further studies showed that people taking the drug consumed 27 per cent fewer calories each day than those taking the placebo. their metabolism was also more active - and they used more energy while resting and burned up more fat.

Even low doses of the drug helped people lose weight, the study found.

"That was surprising," said Dr Heymsfield. "We didn't expect weight loss at all doses."

However, at high doses, the drug had some unpleasant side effects. People taking larger amounts suffered from stomach upsets, nausea and vomiting, and became more irritable.

A larger, phase 3, trial of the drug has now started. The first results from the trial are expected later this year.

Dr Heymsfield added: "All we have here is 12 weeks - we don't yet know what will happen at six months or a year."

One in five adults in the UK - almost 10 million people - are clinically obese in Britain.

Taranabant is the second anti-obesity pill to target the brain's cannabinoid receptors.

In 2006, another slimming aid called rimonabant was launched in the UK. Available on the NHS for seriously obese patients, it is taken by around 10,000 people and costs £2 per patient each day.

As well as controlling appetite, weight, energy use and metabolism, rimonabant can also combat a smoker's carving for nicotine.

However, there are concerns about the use of drugs to help people lose weight. Last year, a study in The Lancet, warned rimonabant - which is also known as Acomplia - could increase the risks of mental illness. It found that people taking the drug were 40 per cent more likely to suffer depression.

In America, the US Food and Drug Administration refused to give approval for the drug, following concerns about side effects.