Patents have expired or will shortly on several big sellers, including the blockbuster hypertension drug Prinivil. When patents go, cheap generic knockoffs rapidly kill sales of the original.
Growth of the blockbuster painkiller Vioxx has slowed this year after a study raised questions about whether the drug poses a cardiovascular risk.
GAPS IN THE PIPELINE
Merck's pipeline of new drugs for the next few years is thin, so investors are anxiously awaiting the company's Dec. 11 analysts meeting. If Merck doesn't outline some potential big sellers, pressure may mount for the drugmaker to make an acquisition or sign a drug-licensing deal.