The revelation that Carlow footballer Ray Walker tested positive for meldonium has put the substance at the centre of the controversy in the spotlight.

Off The Ball exclusively revealed on Tuesday that Walker had tested positive for the substance and that he will served a four-year ban. Walker maintains that his serving of the ban is not an admission of guilt.

However, it throws into light the situation regarding meldonium - so here is a brief explainer of the substance and why it has been listed as prohibited.

What is meldonium?

Meldonium is used to treat angina and heart problems, as it offsets ischaemia - a lack of blood flow to parts of the body.

The drug is made by the Latvian company Grindeks. The manufacturer's website says meldonium gives sufferers of heart and circulatory conditions more "physical capacity and mental function" - and a similar boost to healthy individuals.

It is the substance that Maria Sharapova was also banned for taking, with the Russian tennis star saying that she had been taking it due to a family history of diabetes and a magnesium deficiency. She was banned from tennis for two year in June 2016.

Meldonium's inventor, chemist Ivars Kalvins, has said it was given to Soviet soldiers fighting in Afghanistan to boost their stamina. However, Grindeks and Kalvins have argued it should not be banned in sports, with the manufacturer saying that it "cannot improve athletic performance, but it can stop tissue damage" during intense exercise.

Why was it banned?

The drug, which is also known as Mildronate, was added to the World Anti-Doping Agency's banned list in January 2016.

It had been on the organisation's monitoring programme throughout the previous year. WADA announced the decision on its website more than three months before the ban came into force.

A WADA spokesman said on that meldonium was added to its Prohibited List because of evidence athletes were using it "with the intention of enhancing performance". Studies have suggested the drug can increase a person's capacity for physical exertion.

A study conducted at the European Games in June 2015 and later published by the British Journal of Sports Medicine found 66 of 762 athletes taking meldonium, which the authors called "excessive and inappropriate use [...] in a generally heathy athlete population."

Who has tested positive?

Aside from Walker, most of the notable cases of meldonium transgression have come from the Russian Federation.

Alexander Povetkin, previous opponent of heavyweight boxer Anthony Joshua, had a fight against Deontay Wilder called off following a positive test in 2019.

The 2018 Pyeongchang Winter Olympics were blighted by a positive test from Russian curler Alexander Krushelnitsky.

Sharapova became the second Russian sportswoman to announce a positive test for meldonium. Figure skater Ekaterina Bobrova told Russian agency R-Sport that she had tested positive at the 2016 European Championships, and was ruled out of the World Championships as a result. Russian cyclist Eduard Vorganov also tested positive in the same year.

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