She says it is because a rule change which banned a substance she has been taking in medicine since 2006
Tennis star Maria Sharapova has announced she failed a drugs test at the Australian Open.
The 28-year-old staged a news conference to reveal she tested positive for Meldonium, a substance she had been taking since 2006.
Meldonium was added to the banned list this year.
Sharapova said she did not look at the updated ban list before taking the drug.
She told reporters in Los Angeles: "I wanted to let you know that a few days I received a letter from the ITF (International Tennis Federation) that I had failed a drugs test at the Australian Open.
"I did fail the test and I take full responsibility for it.
"I was first given the substance back in 2006. I had several health issues going on at the time.
"I was getting sick very often and I had a deficiency in magnesium and a family history of diabetes, and there were signs of diabetes. That is one of the medications, along with others, that I received."
The former world number one has not competed since losing to Serena Williams in the quarter-finals on the Australian Open in January.
Sharapova has won five grand slams and is currently ranked sixth in the world.
According to Forbes, she has been the most highly paid female athlete in the world for 11 years straight.
Ahead of the news conference, Sharapova's management said she would make a "major announcement" - sparking speculation she was going to announce her retirement.