According to a new research study, a new obesity drug that jams the biological trigger responsible for cannabis "munchies" is effective even at low doses.

The drug, called taranabant, is the second in a new generation of appetite-reducing weight loss medications.

It follows the lead taken by rimonabant, developed by French pharmaceutical giants Sanofi-Aventis, which was launched in the UK under the brand name Accomplia in 2006. As well as tackling obesity, rimonabant is said to help people give up smoking.

Both drugs block the cannabinoid receptors in the brain that play a key role in regulating hunger and energy balance.

The receptors, which act as molecular switches, also cause some of the well known effects of taking cannabis, including the feeling of hunger nicknamed "the munchies".

Active chemicals in cannabis are similar to the natural "endocannabinoids", produced in the brain, that stimulate the receptors.

Taranabant is being developed by Sanofi-Aventis's rivals Merck & Co.

Study leader Dr Steven Heymsfield, from the company's research laboratories in Rahway, New Jersey, US, 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."

Early research on animals suggested that taranabant could cause weight loss at doses that block just 30% of cannabinoid receptors. A clinical trial involving 533 obese patients then showed that the drug induces significant weight loss at doses ranging from 0.5 to six milligrams over 12 weeks.