Maria Sharapova was reportedly warned "five times" about banned drug moldonium in December.
Players were informed of changes to the WADA banned list for 2016 via multiple emails, through links on notable websites and they even received wallet cards with a list of banned substances for this year.
The former world No.1 said she has used the drug for ten years and was unaware that it had recently been added to the WADA banned list.
However, The New York Times have reported that Grindeks, the Latvian manufacture of the drug recommends only a four to six week course of the medication.
"Depending on the patient's health condition, treatment course of meldonium preparations may vary from four to six weeks. 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," the company said in a statement.
Sharapova also cited a family history of diabetes as one of the reasons for taking the drug, however, it is not generally prescribed for diabetes treatment.
German anti-doping expert Mario Thevis, who helped develop the test for meldonium, said that it can be used as a performance enhancing drug.
"There is a potential of the substance to enhance performance and it has been described as a means to facilitate recovery and to enhance physical as well as mental workload capabilities," Thevis, told the Associated Press.
"It can be tested as reliably as any other doping agent."
While the drug has only officially been on WADA's banned list since January 1st this year, it has been on the list of highly-monitored substances for the past year.
Three of Sharapova's major sponsors, in Nike, Porsche and TAG Heuer, have all suspended their deals with the five-time Grand Slam champion and more are sure to follow.
She could face a two to four year ban.