Adults with a BMI of 28 or more will be able to get orlistat
A pill said to help dieters lose extra pounds is to go on sale over the counter in the UK for the first time.
Orlistat - brand name Alli - has been licensed for prescription in the UK for more than 10 years.
Overweight people will be able to get the drug from chemists for £50 for a month's supply from Wednesday.
The pill, which works by blocking the absorption of fat in the body, is aimed at adults with a Body Mass Index (BMI) of 28 or more.
Manufacturer GlaxoSmithKline says its clinical trials show adding orlistat to a reduced-calorie, lower-fat diet, can help people lose 50% more weight than dieting alone.
But if they persist in eating fat, they will experience some nasty side-effects such as diarrhoea and gas problems.
The Royal College of GPs has advised that the side-effects of the drug are very unpleasant in many people and that it should only be used with support and dietary advice.
The organisation said everyone who wanted the pill should go to their GP for advice because some of them would have treatable causes for their obesity, and all of them would have risk factors for other illnesses which would need to be discussed.
Dr Matt Capehorn, from the National Obesity Forum, warned the drug was not a magic bullet, had a proven track record of being effective and safe.
ONE MAN'S EXPERIENCE
Mike Hare lost 15 stone (95kg) in two-and-a-half years using Orlistat.
He says it was a good kick start - but was far from perfect.
He said: "I hated the side effects. They really were acutely embarrassing at times and very restricting."
He said: "It is a credit to the company that they have resisted the temptation to make it available like your toothpaste or paracetamol - where you can go in, buy it, take it to the till and walk out.
"It is still only going to be available as part of a structured weight management programme."
David Pruce, director of policy and communication at the Royal Pharmaceutical Society, welcomed the drug.
He said: "A lot of pharmacists are already helping people with weight management, and what this does is it gives us another weapon in the armoury to help people in the fight against obesity."
Orlistat has been available over-the-counter in the US for two years.
However, Dr Donald Hensrud, an expert in nutrition at the Mayo Clinic in Minnesota, warned that the impressive results achieved by the drug in tightly-controlled clinical trials would not necessarily be replicated in the real world.
He said people who took the drug for a couple of months, but then stopped would probably find that any weight they lost would be put back on.
And he stressed the pill could not work without accompanying lifestyle changes.
Dr Hensrud said: "In general weight loss is difficult and people are always looking for the easy answer.
"If they think this pill is going to do it for them, and is going to be the answer to their problems, and they can indulge a little bit more I think they will be quite disappointed."