An arbitrator has officially cleared Olympic gold medalist Gil Roberts after he argued that he ingested a banned substance after kissing his girlfriend.

Roberts, a 4x400m relay gold medalist at the Rio Olympics, was provisionally suspended by the United States Anti-Doping Agency in May after his A and B samples tested positive after a drug test in March.

The positive sample confirmed a masking agent called probenecid was in his system.

Last month, an independent arbitrator cleared Roberts of any wrongdoing, which allowed him to compete in the USATF Outdoor Championships.

Roberts said that he ingested probenecid through “frequently and passionately” kissing his girlfriend days before his March drug test.

Roberts’ girlfriend had received a sinus infection medication labeled Moxylong from a local "chemist" during a trip to India with her family, and was still taking the medicine upon her return to the United States.

"He had no idea that kissing his girlfriend could lead to his ingesting a prohibited substance. When he kissed her he did not remember the taste of medicine in her mouth," the arbitrator said.

"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."

Roberts ran in the 400m at the USATF Outdoor Championships and qualified for the world championships in London next month.