Information about serious side effects from drugs such as Merck & Co. Inc.‘s withdrawn Vioxx could get to the public quicker if regulators had the power to write the warning labels themselves, a U.S. drug official told Congress on Tuesday.

The Food and Drug Administration cannot require a company to add a specific warning to a drug label, said Dr. Sandra Kweder, deputy director of the FDA’s Office of New Drugs. The agency negotiates the wording with the manufacturer.

Talks took an unusually long time - more than a year - when Merck and the FDA were crafting a warning about heart risks for Vioxx, Kweder told the Senate Health, Education, Labor and Pensions Committee.

Merck rejected several FDA proposals, and the FDA turned down many of Merck’s, she said.

The warning was added to the Vioxx label in 2002. Merck pulled Vioxx from the market in September 2004 after more research tied the drug to heart attacks and strokes.

“A strong ability to require changes in a label could be very helpful,” Kweder said, adding it would only be necessary “under extreme circumstances.”

A series of safety concerns involving medicines already on the market have put FDA under fire.

Senators said they are considering whether to give the FDA more authority or to restructure the agency so it can better respond to safety concerns about drugs after they win approval.

“Overreacting could be as dangerous as doing nothing, so we must take extraordinary care to find the right approach,” Sen. Mike Enzi, a Wyoming Republican and the committee’s chairman, and Massachusetts Sen. Edward Kennedy, the panel’s leading Democrat, said in a joint statement.

Before the Vioxx withdrawal, the FDA was criticized for taking months to decide if antidepressant use could increase the chances of suicidal behavior in children and teens.

To blunt the criticism, the agency announced in February it was creating a new drug safety board to improve the monitoring of medicines already on the market. Officials also promised to be more open with the public when side effect concerns arise.

Agency officials now are mulling whether Vioxx should return to the U.S. market. An advisory panel voted 17-15 last month that the drug was safe enough to be sold again.

A decision on the future of Vioxx and other COX-2 inhibitors is expected in the next few weeks, Kweder told reporters.