HARNETT COUNTY, N.C. (WTVD) -- A law enforcement official said eight inmates from Harnett Correctional Institution were hospitalized due to suspected drug overdoses.An internal investigation is underway and local law enforcement is being notified, the official said.Authorities said of the eight inmates hospitalized, one has returned to the prison. Four have been admitted to the hospital and three more remain under treatment and observation in the emergency department.The Lillington Police Department is helping with the investigation. Law enforcement believes a synthetic marijuana called K2 is involved, as some inmates have admitted to using that drug.Harnett Correctional Institution is a medium security prison that can hold about 850 inmates.