To be sure, Sun was banned from competition in 2014, but it was for only three months and for a proscribed substance, trimetazidine, that had been prescribed for angina, a heart condition. When Sun took the drug, it had been on the World Anti-Doping Agency’s list for less than five months, and today is no longer recognized as a stimulant by doping agencies.
http://time.com/4446058/rio-2016-swimming-sun-yang-drug-cheat-china/