A NEW drug based on work by a Scots scientist could be a cure for obesity.

Professor Mike Ashford, a neuroscientist at Dundee University, who created the template for the compound, and staff at Cambridge BioTechnology (CBT), which had developed his work, yesterday revealed the results of experiments using the product in rats.

The rats weighed 500g each after enjoying a high fat diet - ''like eating in McDonald's and Burger King every day''.

Half the rodents were given the compound for three weeks and the rest received a placebo. The second group continued to gain weight but the first set ate 20% less and lost 10% of their body weight. This is the equivalent of a man weighing 20 stones dropping to 18 stones.

Earlier this month, US researchers announced they had found the first safe and quick solution to obesity - but their experiment involved injecting a gene into rodents.

The British team argue that injecting genes into human patients is a controversial, futuristic science while their compound could enter a preliminary human trial next year and be available as pills within seven years.

Professor Ashford, who developed the drug while working at Aberdeen University in the late 1990s, said: ''We are very excited by it. The results look very, very good with the animal work.

''We are reasonably confident that the animal models we are using are a fairly good representation of at least some human obesity.''

A spokesman for CBT, said: ''If the drug is even half as effective in humans then this will be a breakthrough in the fight against obesity.''

If future trials prove successful, the team will have tapped into a market with an estimated value of (pounds) 2.6bn and could change the lives of people dogged with health problems because of their weight.

The drug acts by simulating the action of the hormone leptin, which has long been seen as the key to curing obesity.

Leptin is released from fat and tells the brain when the body has sufficient fat stores. However, it does not work in obese people, though high levels are present in the blood, because saturation prevents the signal being effectively carried to the brain. The drug mimics leptin but is small enough to pass into the brain.

As well as suppressing the urge to eat, the drug also appears to increase the rate of metabolism. With traditional dieting, when people cut their food intake the metabolism can slow, making it more difficult to burn off calories and lose fat.

The rats involved in the experiment burned more energy and the weight they lost was fat tissue only - muscle remained unchanged.

Professor Ashford said he hoped the drug would avoid the side-effects found in many obesity treatments, because it mimicked a hormone in the body.

Obesity is a growing problem in the western world and earlier this month leading doctors predicted that a third of all adults in the UK would be obese by 2020, if current trends continue.

The compound works in animals that are not fat and Professor Ashford admitted the drug could be popular with anyone wanting to diet. He said: ''If we get to clinical trials it would have to be prescription only and it would have to be people who were obese and their health was suffering because of their obesity.''