Leftover medications can be deposited Saturday at several sites on Long Island as part of a nationwide effort to sweep unused prescription drugs out of circulation.

National Prescription Drug Take Back Day, a federal initiative, is aimed at getting potentially dangerous medicines — especially addictive narcotics — out of people’s homes.

The program, which nets millions of pills nationally, is held twice a year, in April and October. Take Back Day is sponsored by the federal Drug Enforcement Administration.

Nearly two dozen sites are part of the program on Long Island. Medications can be anonymously deposited in drop boxes between 10 a.m. and 2 p.m. Saturday.

Most bins are located at police stations across Nassau and Suffolk counties. On the DEA’s website at www.dea.gov, residents can search for collection sites by entering their ZIP code or county/city/state.

In Freeport, for example, the police station at 40 N. Ocean Ave. is taking part. In Northport, the police division at the Northport VA Medical Center, 79 Middleville Rd., is a participant.

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Adrienne Esposito, executive director of the Farmingdale-based Citizens Campaign for the Environment, said while a spotlight is focused on narcotics, she sees the program as a way to safely dispose of antibiotics, anticonvulsants, antidepressants, cholesterol-lowering drugs and a host of other categories.

Flushing unused or expired medicines down a toilet is one of the worst forms of disposal because of the drugs’ threat to water supplies, Esposito said.

“Pharmaceutical drugs are classified as an emerging contaminant, which means we are seeing more and more of them in bodies of water, and this can be groundwater or surface water,” she said Friday.

“These drugs are designed to last in water, and on Long Island they are already contaminating our underground as well as our tributaries and bays,” she said.

Gerry Lennon oversees the Take Back Day site at Adelphi University in Garden City, which has participated in the program for the past seven years.

“I think this is important because it keeps drugs out of the water table on Long Island,” he said, adding that safe disposal also eliminates the possibility of narcotics making their way into the wrong hands.

Lennon said he got a jump on the program by starting a day early for people who couldn’t come on Saturday. By Friday afternoon, his collection site at the university’s Public Safety Command Center in Levermore Hall already had made a major haul.

“I have two 30-gallon garbage bags filled already and that’s just for today,” he said.