BEIJING - Sun Yang's national 1,500-meter freestyle title was stripped as the star swimmer had failed a doping test during the national championships this May, announced the Zhejiang Swimming Association Monday.

The multi-Olympic and world champion tested positive for stimulant trimetazidine on May 17 during the national swimming championships and had been banned for three months till August 16, China Anti-Doping Agency (CHINADA) told Xinhua on Monday.

"I have taken many doping tests during years of training and competition and I had never failed one before," said Sun, the Zhejiang native, who was also fined 5,000 RMB ($816).

"I was shocked and depressed at that time, but at the same time it made me cherish my sporting life even more. I will take it as a lesson and be more careful in the future."

The Zhejiang Swimming Association said the provincial association and some related officials were also punished by the Chinese Swimming Association.

Sun gave up the chance to have the B sample tested but defended himself in a July hearing where the experts decided to hand him a three-month ban.

Sun said he used the drug for medical reasons and had been unaware that it was listed in WADA's 2014 prohibited list. Trimetazidine is able to increase coronary flow reserve and was added to the prohibited list in January 2014.