People will be able to drop off expired, unused and unwanted medications on Saturday at sites across the region.

Many police departments, as well as some other government agencies, will be collecting the drugs from 10 a.m. to 2 p.m. as part of the Drug Enforcement Administration’s third national Take Back Initiative.

The drop-offs, which are free and anonymous, are part of the DEA’s effort to curb prescription drug abuse by encouraging the safe disposal of medications.

About 7 million Americans 12 and older abused prescription drugs in 2009, a 13 percent increase from the year before, according to the National Drug Intelligence Center. In the Baltimore-Washington area, prescription drug abuse has become a particular problem among teens and young adults, according to the center.

The DEA collected 18,537 pounds of prescription and over-the-counter medications in the Washington region in April during the last disposal event, according to Ava A. Cooper-Davis, who oversees the DEA’s operations in the District, Maryland, Virginia and West Virginia.

Lucille Baur, a Montgomery County police spokeswoman, said demand during the April disposal event prompted the department to increase the number of drop-off sites from two to six.

Prince George’s County police reported that they collected more than 109 pounds of medication during the April event; Alexandria police said they collected 122 pounds of medication.

Thirteen disposal sites will be in the District. Dozens of sites will be in suburban Maryland and Virginia, too. To find local collection sites, visit the DEA’s Web site.

Cooper-Davis said that people came to events on the last drop-off day with “bags full of prescription drugs.”

“They thank us because they’re not sure how to dispose of these drugs safely,” she said.

The two ways people most often dispose of prescription drugs — in the trash or down the toilet — present major problems, Cooper-Davis said. Drug users sometimes search through piles of garbage for disposed drugs. Meanwhile, drugs flushed down the toilet pose environmental risks to the water supply and the Potomac River.

“If you have to dispose of drugs, we recommend mixing them with coffee grounds or cat litter before throwing them away,” she said.