The Russian, 28, tested positive for meldonium, a substance she has been taking since 2006 for health issues.
The International Tennis Federation (ITF) said the five-time Grand Slam champion would be provisionally suspended from 12 March.
Sportswear company Nike said it was halting its relationship with her until the investigation was complete.
“I did fail the test and take full responsibility for it,” said Sharapova, who won Wimbledon as a 17-year-old in 2004.
Sharapova has been the highest-earning female athlete in the world in each of the past 11 years, according to the Forbes list.
With career earnings from tennis alone amounting to almost £26m, she claimed she had taken meldonium “for the past 10 years” after being given it by “my family doctor” but had known the drug as mildronate.
“A few days ago, after I received a letter from the ITF, I found out it also has another name of meldonium, which I did not know,” she said.
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.
Sharapova was subsequently 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.
Maria Sharapova could face a four years ban if found guilty and could be a big setback to women tennis sport which had made a tremendous improvement in the last decade.
Source: BBC Photos: Courtesy