HARRISBURG, Pa. (AP) — Officials say inmates at a Pennsylvania prison received drugs from the outside hidden beneath the postage stamps on their mail.

Five inmates and six of their loved ones face charges in a sting dubbed “Operation Postage Stamp.” Prosecutors said Monday the inmates’ family and friends used stamps to cover up doses of a prescription drug available in the form of a thin film meant to be dissolved under the tongue.

Prosecutors say the doses of Suboxone would be concealed under the stamps of letters and mailed to inmates at the Carbon County Correctional Facility.

Suboxone is a prescription narcotic used to treat heroin addiction.

The state attorney general’s office says more charges are possible.

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