Days after Russian tennis superstar Maria Sharapova admitted to testing positive for the recently banned substance Meldonium at the Australian Open, the World Anti-Doping Agency (WADA) said on Friday they have recorded 99 positive tests for the drug.

WADA didn't name athletes who tested positive for Meldonium, which has been linked to increased athletic performance. There is a four-year standard ban for the drug under the World Anti-Doping Code.

"We can confirm that since 1 January 2016 when the substance Meldonium became banned, there have been 99 adverse analytical findings for Meldonium recorded," WADA spokesman Ben Nichols said in an email to Reuters and The Associated Press.

"These cases were analyzed by a number of different WADA-accredited laboratories and reported by many different NADOs and international sport federations."

Meldonium, which is sold under the brand name Mildronate, is manufactured in Latvia, and is neither approved by the Food and Drug Administration nor authorized by other European nations. 

There have been varied reports about whether Meldonium is, in fact, a performance-enhancing drug. It reportedly may be an effective treatment of heart conditions and can improve people's mood and endurance.

“The evidence around whether it is a performance-enhancing drug is quite thin,” Mark Stuart, a London pharmacist on the medical and anti-doping commission of the European Olympic Committees, told the New York Times.

“I can’t see how so many athletes — young, quite fit and healthy — would really have a need for this particular drug.”

Sharapova is one of 15 athletes who have been named in testing positive for the drug. Thirteen of the 15 athletes are from the former Soviet Union, of which 10 are from Russia. 

Sharapova has been provisionally banned from tennis. WTA chief executive officer Steve Simon stated on Monday that he was "saddened" by the news.

"This matter is now in the hands of the Tennis Anti-Doping Program and its standard procedures," Simon said, according to the WTA's official website. "The WTA will support the decisions reached through this process."