Russian hurdler Sergey Shubenkov has been cleared of doping in what the Athletics Integrity Unit (AIU) called on Tuesday a "genuinely exceptional" case.
The 2015 world champion in the 110m hurdles had tested positive for acetazolamide, a masking agent, in an out-of-competition test in December 2020.
"After a thorough investigation of the athlete's explanation... the AIU accepted that the positive finding resulted from his unintentional ingestion of residue from medication being used to treat a family member," said the AIU in a statement.
Shubenkov, 30, blamed the positive sample on medication that was being given to his baby.
"My three-month-old son was prescribed a drug from the WADA (World Anti-Doping Agency) banned list," the Russian wrote on his Instagram account on Tuesday.
"A child this age cannot swallow, so we had to prepare the pills in a certain way.
"That left tiny traces of powder from the treatment in my kitchen which generated this positive test."
The decision opens the door to the possibility of Shubenkov competing at next month's Olympics in Tokyo although he has yet to figure on the list of Russian athletes who can compete internationally under a neutral banner, their federation still being suspended.