The use of meldonium – the banned substance taken by tennis star Maria Sharapova –is widespread among elite athletes, new research reveals.

Up to 490 athletes during the Baku 2015 European games, according to the study, which is published online in the British Journal of Sports Medicine.

Sharpova was suspended after she failed a drug test. She admitted to taking the substance, but said it was prescribed by her doctor and she hadn’t noticed it had been banned as a performance enhancing drug.

The substance, known as meldonium or mildronate, is not approved for sale in the U.S. but is prescribed elsewhere to help protect heart tissue by regulating enhancement. Sharapova admitted to having taken it after it was banned by the World Anti-Doping Agency as a performance enhancer.

Over 6,000 athletes from throughout Europe competed in the Azerbaijan event last June,  nearly six months before the substance was banned in January.

Up to 490 athletes may have been taking the substance, according to the report, which drew upon information volunteered by athletes, individual medical teams and lab data.

Highlights of the report included the following:

• 13 medalists or competition winners were taking meldonium.
• 66 athletes tested positive for the substance.
• Meldonium was detected in athletes competing in 15 of the 21 sports in competition.
• Meldonium use was significantly under reported by the athletes.

The study was done as part of a monitoring program on behalf of the European Olympic Committees and led in part to the decision to ban it, the journal article reported.