Cannabis research has led to a British breakthrough that could lead to new ways of fighting obesity, controlling pain and combating cancer, it has been revealed.

The discovery emerged from work on tackling obesity by reversing the "munchies" effect well known to cannabis users.

One appetite suppressant, Rimonabant, has already proved itself in patient trials and could soon appear in clinics. It operates by acting on brain molecules that are receptive to cannabis and natural body compounds similar to those in the drug.

One effect of stimulating the "endocannabinoid" receptors is to induce "the munchies" - a craving for sweet foods often experienced by cannabis smokers. Blocking the system can inhibit hunger and help a person lose weight.

Rimonabant, being developed by French pharmaceutical company Sanofi-Aventis, adopts this principle. In a Belgian study reported in The Lancet medical journal in April, a group of obese patients given Rimonabant lost nine pounds in a year and three inches off their waistlines.

Not only do the receptors promote a feeling of satisfaction after eating, they also encourage the storage of food as fat. Their involvement in a "reward" system also has a bearing on addiction. For this reason Rimonabant has been hailed as a "wonderdrug" that not only sheds pounds, but also helps people to quit smoking.

British scientists led by Professor Roger Pertwee, a neuropharmacology expert from the University of Aberdeen, have been looking at a drug which works in the same way as Rimonabant. But along the way they made a much more significant discovery - a compound that acts as a "volume control" for endocannabinoid receptors.

Laboratory tests show that the compound, called an "allosteric enhancer" can alter the way the receptors respond to stimulating chemicals.

Turning a receptor down suppresses appetite, while turning it up may have a number of beneficial effects, including pain relief and possibly protection against cancer.

Prof Pertwee told the BA Festival of Science at Trinity College, Dublin: "We have discovered a way of amplifying what comes out of the receptor. It's the equivalent of a volume control on the receptor, and that opens up another way of developing drugs. Another way of looking at it is as a dimmer switch. You can dim the light or make it brighter."