Answer
In 2013, Yuliya Yefimova's world short-course records were invalidated due to a positive doping test result for the banned substance meldonium. The substance was added to the World Anti-Doping Agency (WADA) prohibited list on January 1, 2016, but Yuliya had tested positive for it in March 2014. As a result, her results from March 7, 2014, onwards were disqualified, including her short-course world records.