Doctors’ negative reactions to a failed study on Vytorin, a top cholesterol-fighting drug marketed by Schering-Plough and Merck, have probably left some of the companies’ own executives clutching their chests.

Prescriptions for Vytorin and Zetia, another Schering-Plough cholesterol drug, have dropped nearly 20 per cent since mid-January, after a study showed they were no better at avoiding heart disease than older drugs already on the market.