Two separate initiatives - by drkoop.com and Medscape Inc - aim to regulate advertising, content, sponsorship and privacy, following public concern over the accuracy of information available on web sites and how they use personal data collected from consumers.

Medical ethicists, patient advocates and others complain that much of the information available on the 15,000 or more medical web sites is misleading and potentially harmful.

They argue that internet health companies do not distinguish unbiased medical content from adverts or promotional material.

The US push for regulation follows several lawsuits against web sites for allegedly criminal conduct.

In October, Illinois sued four online pharmacies and affiliated doctors, saying they had violated several state licensing and medical practice laws, placing consumers' health at risk.

Financial ties

Illinois was the third US state - after Kansas and Missouri - to file a suit against internet prescription sites.

The American Medical Association has developed guidelines for health web sites with the US Food and Drug Administration, which were adopted by the Association of Medical Publishers.

UK medical bodies have called for similar initiatives to protect patients.

Dr Simon Fradd, Chairman of the British Medical Association's Doctor-Patient Partnership said the best solution would be to promote a handful of validated web sites.

"The proliferation of web sites means that regulation would be difficult, so I'd like to see bodies such as the National Institute for Clinical Excellence providing reliable information."

Roger Goss, director of Patient Concern, warned that that regulation could lead to censorship.

"My view is that it is up to patients to access as much information as they want and then check its validity with their GP."