The official said Friday a customs canine sniffed Heaton's luggage when he arrived at Los Angeles International Airport last Saturday and officers found traces of cocaine.
The official said Heaton, a British citizen, was refused entry into the U.S. at the airport and returned to London. He wasn't arrested because the amount wasn't enough to warrant any charges.
The official couldn't discuss the matter publicly and spoke to The Associated Press on condition of anonymity.
Heaton stars as Jonathan Byers in the Netflix supernatural drama. His publicist didn't respond to a request for comment Friday night.