GlaxoSmithKline, the UK-based pharmaceutical group, will launch on Wednesday the first weight-control drug to be "switched" from prescription to over-the-counter sales in the US.

Alli, designed to tap into the large and growing concern about obesity, will go on sale in pharmacies and other outlets in the US priced at about $55 a month, closely linked to an advertising campaign designed to stress that it should only be used in conjunction with weight loss programmes.