Maria Sharapova was speaking at a news conference in Los Angeles
Former world number one Maria Sharapova has revealed she failed a drugs test at the Australian Open.
The Russian, 28, tested positive for meldonium, a substance she has been taking since 2006 for health issues.
Sharapova, a five-time Grand Slam champion, is provisionally suspended from 12 March pending further action.
"I did fail the test and take full responsibility for it," said Sharapova, who won the Wimbledon title as a 17-year-old in 2004.
"For the past 10 years I have been given a medicine called mildronate by my family doctor and a few days ago after I received a letter from the ITF [International Tennis Federation] I found out it also has another name of meldonium, which I did not know."
Sharapova, who lives in Florida, provided the anti-doping sample in question on 26 January, the day she lost to Serena Williams in the Australian Open quarter-finals.
The World Anti-Doping Agency (Wada) analysed the sample and returned a positive for meldonium, leading to the Russian being charged on 2 March.
"It is very important for you to understand that for 10 years this medicine was not on Wada's banned list and I had been legally taking that medicine for the past 10 years," said Sharapova.
"But on 1 January the rules had changed and meldonium became a prohibited substance, which I had not known."
She added: "I received an email on 22 December from Wada about the changes happening to the banned list and you can see prohibited items - and I didn't click on that link."
Maria Sharapova wins Wimbledon in 2004
Sharapova has been the highest-earning female athlete in the world for the past 11 years, according to the Forbes list. Her career earnings from tennis alone amount to almost £26m.
She first reached world number one in August 2005 and is currently seventh in the rankings - but she has played just four tournaments since Wimbledon last July as she struggled with an arm injury.
Sharapova, who turns 29 in April, hopes to be able to return to tennis in the future.
"I made a huge mistake," she said. "I have let my fans down, and let the sport down that I have been playing since the age of four that I love so deeply.
"I know that with this I face consequences and I don't want to end my career this way. I really hope to be given another chance to play this game."
There had been speculation Sharapova was going to announce her retirement and a large media contingent gathered for the Los Angeles news conference, which was streamed live online.
"I know many of you thought that I would be retiring today but if I was ever going to announce my retirement it would not be in a downtown Los Angeles hotel with this fairly ugly carpet," she said.
Women's Tennis Association (WTA) president Steve Simon said he is "very saddened" at Sharapova's failed test.
"Maria is a leader and I have always known her to be a woman of great integrity," he added.
"As Maria acknowledged, it is every player's responsibility to know what they put in their body and to know if it is permissible.
"This matter is now in the hands of the Tennis Anti-Doping Programme and its standard procedures. The WTA will support the decisions reached through this process."
Eighteen-time Grand Slam champion Martina Navratilova said: "Hope this gets cleared up as it seems to me to be an honest mistake."
Brad Gilbert, who coached Andy Murray from July 2006 to November 2007, said: "Still stunned that nobody on 'Shazza' team checked new list from Wada. Players are responsible but this is big-time oversight on team as well."
Former athlete Kelly Sotherton, who won bronze in the heptathlon at the 2004 Olympics, said it was "refreshing" that Sharapova took full responsibility for the failed test but "can only blame herself".
She added: "I'm pretty sure if this was a track and field athlete they'd be getting a much rawer deal than Sharapova."