The federal agency received roughly 422,500 adverse-event reports from pharmaceutical companies, health professionals and patients, up nearly 14% from the 370,887 reports filed in 2003. A final 2004 total is expected later this year, but FDA officials don't expect it to vary significantly from the estimate.

The bulk of the reports comes from drug manufacturers, which the FDA requires to file details of all known adverse events involving their products. Doctors, nurses and patients also file, but their reports are voluntary. As a result, the annual totals are believed to cover only a percentage of the actual number of serious drug reactions and problems.

Although the 2004 increase occurred during a year that saw rising questions about prescription drug safety, a top FDA official said the agency believes the rise reflects a surge in prescription drug use, not any increase in health risk.

"There are more drugs on the market and more use of pharmaceuticals in general," said Paul Seligman, director of the FDA's Office of Pharmacoepidemiology and Statistical Sciences. "Clearly, when you have more products on the market, you're likely to have more side effects."

Prescription drug sales totaled $235 billion nationally in 2004, a historic high that was up 8.3% from 2003 and more than triple the 1995 volume, according to IMS Health, a pharmaceutical market research firm.

Sidney Wolfe, director of Public Citizen's Health Research Group, a Washington-based consumer watchdog, agreed that increased use of prescription drugs offered one explanation for the jump in adverse-event reports. But he suggested that increased doctor and consumer understanding of the power of prescription drugs could play an important contributing role.

"There's much more public awareness of the potential for drugs to cause adverse reactions," Wolfe said. "The whole concept of drug-induced disease is much better known than it was 10 or 15 years ago."

Seligman said FDA analysts are examining the most recent data as part of the agency's continuing mission to identify and address drug-safety problems. "More reports offer us an opportunity to detect safety concerns," he said.

There was "no unusual acceleration" of reports filed in the final quarter of 2004, Seligman said. That seemed to indicate Merck's September withdrawal of the painkiller Vioxx from the market — an event that generated new concern about government oversight of drug safety — didn't spur a rush of new concerns.