Police said Harris was driving and Williams the front passenger in a white Chevrolet Impala that was stopped for speeding in the 500 block of West Fairview Avenue.
Police said the driver had a suspended license and the vehicle had to be towed.
During a search of the vehicle’s inventory, police found gel caps of the drugs in bags under the front seats, according to the report.
Two other rear passengers were not arrested.
Police credited the department’s work with the Phoenix Project, in which an officer is assigned to patrol around Good Samaritan Hospital.
Dayton Lt. Wendy Stiver said Since Jan. 14, the project has netted more than 50 traffic citations and 16 arrests for warrants, drugs and weapons.
Harris and Williams are being held in the Montgomery County Jail.