Five-time grand slam champion and former world number one tennis player Maria Sharapova has admitted to failing a drug test at the Australian Open in January.

Sharapova tested positive for meldonium, also known as Mildronate - a substance she said she had been taking for 10 years, but was added to the banned list just this year.

Dr Peter Brukner, a leading sports doctor and professor of sports medicine at La Trobe University, explained to ABC NewsRadio what the drug is and why it is used.

What is meldonium?

Meldonium is an anti-ischemic drug that helps improve circulation, particularly in the brain.

It is produced out of Latvia, has been around for some time and is commonly used in northern Europe.

It is also used for heart conditions such as angina (where there is restricted blood flow to the heart), heart attacks, heart failure and sometimes after strokes.

It has also been rumoured to have been used by athletes for some time.

Is it performance enhancing?

This is the conclusion that the World Anti-Doping Agency (WADA) have come to - that it is there to improve performance.

When was it added to the WADA banned list?

Sorry, this video has expired Sharapova drug test: What is meldonium?

On January 1, 2016, it was added to the banned list.

It was not done with a lot of fanfare. However, it is the athlete's business to know what is on the banned list and the business of the sport to let people know what is happening.

The banned list is readily available. Every doctor has access to it and every year they announce what substances have been added to it.

The World Anti-Doping Authority put it on its monitoring list last year to keep an eye on its use and try and asses how widely it is being used.

In the meantime, there were a number of research projects being done to determine whether it did actually improve performance.

Is it widespread among athletes?

No, not for legitimate reasons.

There have been a few positives in the last little while. There were some Russian dancers who were gold medallists in the [Winter] Olympics in 2014. They tested [positive] last month.

It is a popular supplement, particularly in former Soviet Union countries.

Do we use it in Australia?

I do not think we see too much of it [in Australia] and I do not think it is even allowed in the United States.

But it certainly has been around for a while and rumours about athletes taking it started to come to the fore in the last couple of years.

I think it's a fairly controversial drug. It is not used in fairly orthodox medicine as such in Western countries. It is used in northern European countries.