But it’s not just Sharapova. A recent study in the British Medical Journal reports that meldonium was detected in athletes competing in 15 of the 21 sports during the 2015 European Games in Baku—that’s 70% of the sports categories. It also found that 13 medalists were taking meldonium at the time of the Baku Games.

“There was significant under-reporting of the use of this drug by athletes in most sports,” researchers noted in the study. “Only 23 (3%) of the 662 athletes tested self-reported taking the drug, compared to 66 (8.7%) athletes who actually tested positive for meldonium.”

Last year, the World Anti-Doping Agency’s testing center in Germany found that 182 of 8,320 random urine samples gave positive results for the drug. Tom Bassindale, a lecturer in forensic science at Sheffield Hallam University,  described the 2.2% positive rate as “huge.”

The drug was only recently banned on Jan. 1 by WADA, which feared that as meldonium increased oxygen delivery to muscles, it could be abused by athletes trying to increase their endurance. WADA claimed to have warned players five times about the impending banned, warnings that clearly went under Sharapova’s radar—a lesson to check those emails.

Sharapova claimed to be taking meldonium for over a decade to treat magnesium deficiency, heart problems, and to combat a family history of diabetes.

Meldonium is currently not approved by the FDA in the United States, but it reportedly remains popular in Baltic countries. The drug has a rather bizarre history; it was widely used in the 1980s as a stamina enhancer by Russian troops stationed in Afghanistan.

The issue around Sharapova and other athletes use of meldonium as a performance enhancer is part of a wider problem of doping in sport. WADA is currently playing a cat-and-mouse game with athletes—a game it’s is clearly losing, because every time WADA bans a certain drug, athletes find a way to better conceal the performance-enhancers they’re using.

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