Hydrochlorothiazide is a diuretic used as a masking agent, or a compound that hides the presence of other illegal drugs by lowering the level of the banned substances in urine.

Chen tested positive for the banned substance on Aug. 7, and she has already submitted a second sample for testing, according to state broadcaster CCTV on its Weibo account (link in Chinese, registration required). A spokesperson for the Chinese Swimming Association said that Chen is required to cooperate with Olympic authorities, according to CCTV.

Chen came 4th in the 100-meter butterfly finals on Aug. 8, and was due to compete in the 50-meter freestyle on Aug. 13. She was a gold medalist in the 2014 Asian Games in Incheon, South Korea.

📬 Sign up for the Daily Brief

Our free, fast, and fun briefing on the global economy, delivered every weekday morning.