New treatment performs better than rivals and without the side effects

People taking the highest dose of a new anti-obesity drug lost more than a stone in weight in 20 weeks, a study has shown.

The amount of weight lost was almost three times that in a control group given a placebo and 50 per cent more than those given a rival treatment, which is the current brand leader for the treatment of obesity.

The drug, liraglutide, is the first of a new class of anti-obesity agents which mimic the action of a hormone that occurs naturally in the gut, reducing hunger. Experts said it had "great potential" because it also reduced the risk factors for Type 2 diabetes and heart disease. Diabetes already affects more than two million people in Britain and is rising so fast it threatens to overwhelm the NHS.

But they warned that the high cost of the drug – around £500 for six months' supply at the lowest dose – could limit its use.

Liraglutide, made by Novo Nordisk, was licensed earlier this year as a treatment for diabetes and trials have so far shown it is safe. In the first study in obese people without diabetes, published today in the Lancet, it has been shown to significantly reduce weight, with few side effects.

The study was conducted among 564 adults with a body mass index of over 30 and treated at 19 hospitals across Europe. They were put on a diet containing 500 calories fewer than they needed each day, combined with an exercise programme and given liraglutide (in one of four different doses), or orlistat (brand name Xenical, the most popular anti-obesity treatment) or a placebo.

Those on the highest 3mg dose of liraglutide lost 7.2kg on average (almost 1 stone 2lb) over 20 weeks, compared with 2.8kg on the placebo and 4.1kg with orlistat. Liraglutide cut blood pressure and improved blood glucose control, reducing the risk of diabetes.

Professor Arne Astrup, head of the department of Human Nutrition at the University of Copenhagen, Denmark, who led the study, said: "The reason why we think this drug is so intriguing is that it mimics a gut hormone called GLP-1 which is released in the small intestine after eating. It tells the body to produce more insulin and the brain to stop eating. It is a naturally occurring satiety hormone. The problem is that it is eliminated from the blood stream within minutes. The company [Novo Nordisk] has added a molecule to make it more resistant to elimination, so it lasts for a full day."

Side effects were limited to nausea and vomiting in some patients, which was easily controlled by reducing the dose of the drug, Professor Astrup said. It has to be given by injection under the skin, because the drug would be broken down in the gut, but patients found this simple using a pen-like injector similar to those used by diabetics.

Professor Astrup is a paid consultant for Novo Nordisk, but an acknowledged leader in obesity research and his paper was submitted to peer review. He said: "This class of compounds [GLP-1 analogues] have a great future if our knowledge today holds. They are very safe and they not only reduce weight but reverse risk factors associated with diabetes. The fact that they [are administered by] an injection means that a commitment from patient and doctor is needed and they are less likely to be used for purely cosmetic reasons."

Dr Colin Waine, the former chairman of the UK National Obesity Forum, said that the safety of the drug had been confirmed in trials in diabetics.

"This is the first trial I know of in non-diabetic patients. The weight loss is very significant. This class of drugs has great potential in both diabetics and non-diabetics. Professor Astrup is a world authority on obesity – this is a very promising development. But it is quite an expensive drug and that could limit its availability. We will have to see how the National Institute for Clinical Excellence rates it for cost effectiveness."

In an accompanying comment in the Lancet, George Bray, an obesity specialist at Louisiana University, US, said he was "optimistic" that the promise of the new class of drugs "will be fulfilled".

Weight pills: Drugs that help shed the pounds

Orlistat (Xenical) Also available over the counter as Alli Weight Loss Pills

It works by blocking the action of an enzyme that digests fat in the intestine and stops about a quarter of the fat eaten from being absorbed. Your body does not use the calories contained in this fat, so you start to lose weight. However, this unabsorbed fat has to go somewhere and users are prone to diarrhoea.

Sibutramine (Reductil)

Developed as an anti-depressant, it was found to aid weight loss. It boosts the levels of the neurochemicals serotonin and noradrenaline in the brain, reducing appetite. Side effects include a rise in blood pressure.

Liraglutide (Victorza)

Developed as a treatment for diabetes, it was shown to lead to weight loss. It mimics a naturally occurring gut hormone which acts on the brain, reducing hunger, and delays the emptying of the stomach, so feeling full lasts for longer. It also reduces blood pressure and helps prevent poor glucose control – cutting the risk of cardiovascular disease and diabetes.