Olympic gold medalist Gil Roberts, who was suspended in May for a positive drug test, has had that decision reversed by an arbitrator, who upheld the sprinter's defense that the drug was in his system due to frequent and passionate kissing of his girlfriend.

A professional since 2009, Roberts was part of the United States' 4-by-400 relay team that won gold at the 2016 Rio Olympics.

In March, he tested positive for a drug called probenecid, and in May, the United States Anti-Doping Agency said Roberts' B sample also tested positive for the masking agent.

The case went to an arbitrator in June.

As part of the evidence, the stepfather of Roberts' girlfriend said she was in India a few weeks before the March test and came down with a sinus infection. A local "chemist" there directed her to take one capsule of Moxylong per day for a period of two weeks.

The woman, Alex Salazar, continued to take the medicine when she returned to the U.S., breaking the capsule apart and pouring its contents into her mouth before swallowing with water. USADA said the sides told the arbitrator that Roberts and Salazar "kissed frequently and passionately" when they were together, including on March 24, when Roberts was initially tested. Salazar ingested the medicine that afternoon, the two kissed after that, and the doping officer arrived three hours later. Salazar was unsure how many times they kissed between when she took the medicine and when Roberts was tested.

Roberts testified that he did not know that kissing his girlfriend could lead to a positive test, nor did he know she was taking Moxylong.

"Thus, for Roberts, it must have been like lightning out of a clear blue sky for him to learn that by kissing his girlfriend this time that he was exposing himself to a prohibited substance. Roberts has met his burden of proof," USADA said in its ruling, released earlier this week.