They are supposed to be prescribed only to obese patients who cannot lose weight by changing their lifestyles - which suggests either that nobody has any will-power or that the marketing tactics of the drug companies are working well.
First on the market were orlistat, approved in 1998, and sibutramine, an antidepressant that was approved as an anti-obesity therapy in 1997 in the USA and in 1999 in Europe.
They've now been joined by rimonabant, which has been approved in Europe, and is likely to get its license in the USA shortly.
Remarkably, the anti-obesity drugs are getting approval with virtually no evidence of their safety and effectiveness. Hardly any studies have been properly carried out because of the vast numbers of participants who drop out long before the end.
The little we know suggests that orlistat and sibutramine achieve a weight loss of less than 5 per cent - half the target suggested by the European drug regulator, the EMEA (European Agency for the Evaluation of Medicinal Products).
Orlistat often causes gastro-intestinal problems, and sibutramine increases blood pressure and pulse rate. Early results back on rimonabant suggest that it can dramatically alter the patient's mood.
As researchers from Canada's University of Alberta Hospital in Edmonton point out, we also don't know what the long-term effects of the drugs are.
(Source: The Lancet, 2007; 369: 71-7).
E-news broadcast 11 January 2007 No.324 [Subscribe]