Gil Roberts, who won Rio Olympic gold on the US men's 4x400-meter relay, was cleared of doping after an arbitrator found he ingested a banned substance by kissing his girlfriend.
According to a final US Anti-Doping Agency (USADA) report in the matter unveiled Thursday, the ruling that cleared Roberts of wrongdoing turned on his girlfriend, Alex Salazar, having taken medicine for a sinus infection that contained the banned masking agent probenecid.
In the weeks before the March 24 positive test by Roberts, Salazar and her family had visited rural India, where she received medicine for a sinus infection that included the banned substance.
Because she had problems swallowing pills, Salazar took apart the capsules and swallowed the medicine inside with water. She returned home and saw Roberts while still taking the medication Moxylong, which contained probenecid.
"Whenever they were together, they kissed frequently and passionately," the USADA report said.
That included the day of the random doping test, when his urine sample was taken in the afternoon about three hours after she had last taken the medicine.
"Roberts had dated Ms. Salazar for two years and surely had kissed her before without being charged with a doping violation," the report 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 was cleared last month, although the kissing background detail was only revealed this week.
The timing allowed Roberts to compete in the 400m at last month's US track and field championships, in which Roberts qualified for the world championships next month in London by finishing second in 44.22 seconds.