Some of the most common and most powerful prescription painkillers on the market will be restricted sharply in the emergency rooms at New York City’s 11 public hospitals, Mayor Michael R. Bloomberg said Thursday in an effort to crack down on what he called a citywide and national epidemic of prescription drug abuse.

Under the new city policy, most public hospital patients will no longer be able to get more than three days’ worth of narcotic painkillers like Vicodin and Percocet. Long-acting painkillers, including OxyContin, a familiar remedy for chronic backache and arthritis, as well as Fentanyl patches and methadone, will not be dispensed at all. And lost, stolen or destroyed prescriptions will not be refilled.

City officials said the policy was aimed at reducing the growing dependency on painkillers and preventing excess amounts of drugs from being taken out of medicine chests and sold on the street or abused by teenagers and others who want to get high.

“Abuse of prescription painkillers in our city has increased alarmingly,” Mr. Bloomberg said in announcing the new policy at Elmhurst Hospital Center, a public hospital in Queens. Over 250,000 New Yorkers over age 12 are abusing prescription painkillers, he said, leading to rising hospital admissions for overdoses and deaths, Medicare fraud by doctors who write false prescriptions and violent crime like “holdups at neighborhood pharmacies.”