A drug that could help obese people drop two dress sizes in six months could be available on the market in three years, its Danish maker has said.

Novo Nordisk, the Danish pharmaceutical producer, claimed that liraglutide could also lower blood pressure levels, raise "good" cholesterol and help control diabetes, the Daily Mail reported today.

The drug, which can be injected using a pen-like device, is based on incretin, a gut hormone that tells the brain when it is time to stop eating but breaks down within minutes of being produced. In contrast, the drug stays in the body for hours.

The company is currently carrying out large-scale, definitive trials on 5,000 obese men and women. It expects them to finish in 2013.

In the first phase of the trials, nearly 550 male and female volunteers, who've struggled with their weight for years, lost an average of a stone-and-a-half over six months, according to the findings.

In that trial, some subjects were given daily doses. Others were given dummy pills.

Those who took liraglutide lost an average of a stone and a half over six months - more than twice as much as those on some dummy pills. In addition, 28 per cent of those on the highest dose of liraglutide shed at least 10 per cent of their weight.

The women dropped an average of three inches from their waistline and male pot bellies also shrank. When they continued to take the drug for a further 18 months, the weight stayed off. But those on dummy pills began to pile the pounds.

And, if all the trials prove as successful as those already carried out, the drug could be routinely given to the obese and overweight in three years, say the scientists.

Viggo Birch, managing director of Novo Nordisk, said: "We have had phenomenal results from the first clinical trials in obesity. The effects on confidence and health were life-changing."

Experts have welcomed the new jab.

Nick Finer, a University College London expert in hormones and weight loss, said the jab could cut the need for gastric bands, stomach stapling and other expensive and potentially dangerous operations.