Antonio Pettigrew was found in his vehicle parked along Highway 751 in Chatham County next to Jordan Lake August 10.
An autopsy revealed a lethal concentration of diphenhydramine - an allergy and sleep aid - in Pettigrew's system.
Pettigrew was entering his fourth season as an assistant coach at the time of his death. He coached sprints, hurdle and relays for the track team.
A 1993 graduate of St. Augustine's in Raleigh, Pettigrew coached at his alma mater for three years as an assistant and then went on the coast at Cardinal Gibbons High School in Raleigh.