Tennis star Maria Sharapova made the shocking announcement on Monday that she had tested positive for a banned substance called meldonium. The highest-paid female tennis player in the world said she had been taking the drug for years and was not aware that the substance had been banned this year before going to the Australian Open.
The announcement has already led to Sharapova being suspended from tennis and to lost endorsement deals, including a multi-million contract with Nike.
Here's some key facts about the little-known drug at the center of the scandal.
What Is Meldonium?
The drug is called meldonium or mildronate and was created for patients with coronary heart disease as a way to relieve chest pain.
The drug is designed to open up blood vessels to get oxygen and blood to muscles and relieve chest pain and strain on the heart.
Where Is the Drug Legal?
The drug is not approved by the U.S. Food and Drug Administration, but it is available in Russia.
The World Anti-Doping Agency put the drug on its prohibited list starting this year. However, it had been a part of the monitoring program for drugs "which are not on the Prohibited List, but which WADA wishes to monitor in order to detect patterns of misuse in sport," WADA said in a statement last year.
Does the Drug Improve Athlete's Performance?
There is not much conclusive medical literature about how the drug impacts athletes, so it's full effects are not yet known.
However, one medical paper published last year said the drug has been have linked to improved endurance in athletes as well as "improved rehabilitation" or ability to recover quickly after exercise.
Another study found that patients with a history of heart problems could exercise longer on a treadmill than their counterparts taking a placebo, but the gains were modest.
Dr. Minh-Chi Tran contributed to this report. She is an internal medicine physician at University of California Davis Medical Center and a resident at the ABC News Medical Unit.