(CNN) Maria Sharapova denies she had been warned five times about the impending ban on meldonium and says she will "fight back" after criticizing elements of the media who "distort, exaggerate and fail to accurately report the facts."

The Russian, 28, admitted Monday to taking the illegal substance , but wrote a letter to her fans on Facebook Friday to saying she makes "no excuses for not knowing about the ban", which came into effect on January 1.

The five-time grand slam winner, who faces a suspension of up to four years, claims the communications from tennis authorities about changes to drugs on the banned list were "too hard to find."

Former NFL linebacker Bill Romanowski appeared on "60 Minutes" in 2005 and admitted to using steroids and human growth hormone during his career.

Former NFL linebacker Bill Romanowski appeared on "60 Minutes" in 2005 and admitted to using steroids and human growth hormone during his career.

Home-run hitter Sammy Sosa was among the players who tested positive for performance-enhancing drugs in 2003, according to the New York Times.

Home-run hitter Sammy Sosa was among the players who tested positive for performance-enhancing drugs in 2003, according to the New York Times.

Baseball slugger Mark McGwire evaded questions about steroid use when speaking to Congress in 2005. But in 2010, he admitted that he had used steroids during the 1990s.

Shawne Merriman, then of the San Diego Chargers, was suspended for four games after testing positive for steroids in 2006. He retired in 2013 after eight NFL seasons.

Shawne Merriman, then of the San Diego Chargers, was suspended for four games after testing positive for steroids in 2006. He retired in 2013 after eight NFL seasons.

Former New Orleans Saints defensive lineman Charles Grant tested positive for banned substances in 2008 and was suspended for the rest of the season.

Former New Orleans Saints defensive lineman Charles Grant tested positive for banned substances in 2008 and was suspended for the rest of the season.

In 2008, Olympic track star Marion Jones was sentenced to six months in prison for lying to federal prosecutors investigating the use of performance-enhancing substances.

Cyclist Floyd Landis admitted in 2010 to using performance-enhancing drugs for most of his career. Landis used the red-blood-cell booster erythropoietin, known as EPO, along with testosterone, human growth hormone and frequent blood transfusions. He was stripped of his 2006 Tour de France win and suspended from cycling for two years.

Houston Texans linebacker Brian Cushing was suspended for four games after testing positive for a drug called human chorionic gonadotropin in 2010.

Houston Texans linebacker Brian Cushing was suspended for four games after testing positive for a drug called human chorionic gonadotropin in 2010.

Barry Bonds, baseball's all-time home run leader, was convicted of an obstruction charge in 2011 after he impeded a grand jury investigating the use of performance-enhancing drugs. Bonds had testified that he thought his personal trainer was giving him arthritis balm and flaxseed oil, not steroids or testosterone.

Barry Bonds, baseball's all-time home run leader, was convicted of an obstruction charge in 2011 after he impeded a grand jury investigating the use of performance-enhancing drugs. Bonds had testified that he thought his personal trainer was giving him arthritis balm and flaxseed oil, not steroids or testosterone.

Mixed martial arts fighter Alistair Overeem failed a random drug test in 2012 and admitted to injecting himself with a substance that contained testosterone, prescribed for a rib injury. He was suspended for nine months.

Mixed martial arts fighter Alistair Overeem failed a random drug test in 2012 and admitted to injecting himself with a substance that contained testosterone, prescribed for a rib injury. He was suspended for nine months.

In 2013, Lance Armstrong admitted to doping throughout his cycling career. The seven-time Tour de France champion confessed to using testosterone, human growth hormone and blood transfusions to enhance his performance.

Ryan Braun of the Milwaukee Brewers admitted to using performance-enhancing drugs in 2011, the year he was National League MVP. He said he took a cream and a lozenge with banned substances while recovering from an injury.

Ryan Braun of the Milwaukee Brewers admitted to using performance-enhancing drugs in 2011, the year he was National League MVP. He said he took a cream and a lozenge with banned substances while recovering from an injury.

Olympic sprinter Tyson Gay was banned for one year after he tested positive for a prohibited anabolic steroid in 2013. The four-time U.S. champion in the 100 meters received a reduced punishment from the two-year suspension standard for cooperating with authorities. The 4x100 relay team he was on was stripped of the silver medal it won in the 2012 Olympics. Gay returned to racing in 2014.

New York Yankees slugger Alex Rodriguez confessed to using performance-enhancing drugs in a meeting with the Drug Enforcement Administration in January 2014. Rodriguez told DEA investigators that he had used banned substances, including testosterone cream, testosterone gummies, and human growth hormone, between late 2010 and October 2012. He was suspended for the entire 2014 season.

In February, New York Mets pitcher Jenrry Mejia became the first player to be permanently suspended by Major League Baseball after he tested positive for a performance-enhancing substance. MLB said Mejia tested positive for boldenone, an anabolic steroid that athletes use to increase muscle mass.

In February, New York Mets pitcher Jenrry Mejia became the first player to be permanently suspended by Major League Baseball after he tested positive for a performance-enhancing substance. MLB said Mejia tested positive for boldenone, an anabolic steroid that athletes use to increase muscle mass.

Maria Sharapova, a five-time Grand Slam champion and the world's highest-paid female athlete, admitted that she failed a drug test at the Australian Open in January. She tested positive for meldonium, a recently banned substance that she said she had taken since 2006 for health issues. She will be provisionally banned by the International Tennis Federation on March 12. Click through the gallery to see other athletes accused of using drugs to boost their careers.

Sharapova said she had been taking the heart drug since 2006 but dismissed reports she took it every day, saying she followed doctors' instructions and took it in the "low doses recommended."

Reports this week suggested the normal course of treatment for patients on meldonium, sometimes known as mildronate, is four to six weeks.

"That headline has been repeated by many reporters who fail to tell their viewers and readers what the rest of the story says," wrote Sharapova.

"The story quotes the manufacturer of my medicine as saying: 'Treatment course can be repeated twice or thrice a year. Only physicians can follow and evaluate patient's health condition and state whether the patient should use meldonium for a longer period of time.'

"That's exactly what I did. I didn't take the medicine every day."

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The World Anti-Doping Agency (WADA) began monitoring the use of meldonium by athletes in 2015, but Sharapova denies being repeatedly warned about it.

'Wrong'

"A report said that I had been warned five times about the upcoming ban on the medicine I was taking," she wrote. "That is not true and it never happened."

Sharapova said the way the International Tennis Federation, the sport's governing body, informed players of the changes were "buried in newsletters, websites, or handouts."

She wrote: "In order to be aware of this 'warning', you had to open an email with a subject line having nothing to do with anti-doping, click on a webpage, enter a password, enter a username, hunt, click, hunt, click, hunt, click, scroll and read. I guess some in the media can call that a warning. I think most people would call it too hard to find.

"No excuses, but it's wrong to say I was warned five times."

Sharapova failed a drug test on January 26 after losing to Serena Williams in the quarterfinals of the Australian Open. She was charged with an anti-doping violation on March 2, and was provisionally banned from March 12.

The ban could be reduced to two years or less if anti-doping officials find Sharapova did not intentionally take the drug to enhance performance.

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