Maria Sharapova failed a drug test at the Australian Open - here's why the medication she took is banned

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Maria Sharapova.

Champion tennis player Maria Sharapova admitted Monday that she had failed a drug test at the Australian Open.

The drug, meldonium, had recently been added to the World Anti-Doping Agency's list of banned substances.

The 28-year-old Russian athlete claims she had been taking the drug since 2006 because of several health concerns, including magnesium deficiency, an irregular EKG (a test of heart function), and diabetes, a condition she said runs in her family.

The drug, used to treat chest pain and damage from a heart attack, has been found to increase exercise capacity and peripheral circulation in patients with chronic heart failure.

In addition, animal studies and small human studies suggest that meldonium, in combination with other drugs, may help treat diabetes.

But the drug is also known to increase the endurance performance of athletes, improve recovery after exercise, protect against stress, and enhance the central nervous system.

That's probably why the World Anti-Doping Agency decided to ban it in January.

Meldonium is legal in Lithuania, but is not approved for use in the US. Before it was banned, meldonium was popular among Russian athletes, according to AP reporter James Ellingworth.

Sharapova claims that she was unaware the drug had been added to the list of banned substances.

"For the past 10 years I have been taking a medicine called mildronate by my doctor, my family doctor, and a few days ago after I received the letter from the ITF [International Tennis Federation] I found out it also has another name of meldonium, which I did not know," Sharapova said, according to the BBC.

She added that she had legally been taking the medicine for the past 10 years.

Former European ice-dancing champion Ekaterina Bobrova also told Russian media on Monday that she had failed a drug test for taking meldonium, the AP reported.