Prosecutors filed charges Wednesday against a former inmate, Michael Romeo Taurino, 30, and three current inmates - Ryan Neil Stephenson, 24, Charles Frederick Shaffer, 33, and Jesse Michael Conklin, 22.
It all began when a letter from one of the suspects bounced back to the prison last month.
Investigators say the letter was opened in accordance with incoming mail search guidelines.
Detectives say the letter contained an offer to buy Suboxone directly from the outside rather than the higher price inside.
The letter prompted officials to monitor incoming mail for dissolving films of Suboxone concealed beneath the stamps.
Suboxone is a prescription narcotic used to treat heroin addiction.
The four men are charged with sending contraband to an inmate, conspiracy, possession of a controlled substance by an inmate and related offenses.