Amid reports that Russia’s entire Under-18 men’s hockey roster is being replaced just one week prior to the IIHF World Championship because of possible doping, more questions are being asked about the recently banned performance-enhancer meldonium.

According to a report from TSN, more than half of the 30 players in Russia’s evaluation camp tested positive for the drug, resulting in the players being replaced by the country’s under-17 team.

The players and the team's coach were removed  and their profiles deleted from the team website without explanation. The Russian Hockey Federation has not responded to the reports linking the sudden roster switch to doping.

The news comes just weeks after tennis star Maria Sharapova drew world attention for announcing she had tested positive for the drug.

Since then, Russia’s men’s curling team suddenly changed its roster ahead of the world championships, and the Russian national volleyball team backed out of the Euro Cup without explanation.

What is this drug and why is its ban affecting Russia? Here’s a look at what we know.

What is meldonium?

Meldonium was developed in the 1970s as a veterinary growth enhancer, although it appears to have never been used for that purpose. Instead, doctors discovered it could be used as a blood-flow booster to treat angina and heart failure, two heart conditions marked by impeded blood flow to the heart.

Why had I never heard of it until this year?

Most Canadians haven’t heard of meldonium because the drug has never been approved for sale in Canada or the U.S., nor has the European Medicines Agency okayed it. But it is used in the Baltic countries, where it is made by the Latvian pharmaceutical company Grindeks and sold under the name Mildronate -- typically sold over the counter.

Sharapova raised the drug’s profile when she announced last month she had tested positive for the drug after competing in the Australian Open. Since then, WADA, the World Anti-Doping Agency, has announced more than 120 positive meldonium tests across several sports.

Is it dangerous?

It’s unclear. Very few studies have been completed on the performance enhancing effects of meldonium, nor on the effects of taking it long-term.

The manufacturers of meldonium say its side effects can include headache, agitation, and heart rhythm disturbances. No serious adverse effects that pose a significant risk to health or life have been documented, but again, research on the drug has been thin.

How is it a performance-enhancer?

WADA has been monitoring meldonium use since 2015 and added it to its list of banned substances on Jan. 1, 2016. The agency says it added the drug because “of evidence of its use by athletes with the intention of enhancing performance.“

It’s not clear how meldonium might enhance performance. According to one study, the drug increases endurance, improves rehabilitation after exercise, protects against stress, and enhances “activations of central nervous system functions."

But not everyone agrees it’s a performance-enhancer, noting that it’s not a well-researched drug.

Its manufacturer, Grindeks, says in its promotional literature that meldonium can improve "physical capacity and mental function" in healthy people. But it has also said it doesn’t believe the drug would enhance athletes' performance -- and might even do the opposite because it slows how the body breaks down fatty acids to produce energy.

Is meldonium banned in all of hockey?

Meldonium is not banned by the NHL, and the league does not test for it even though there are reports that eastern European athletes use it widely.

Exercise physiologist Dr. Greg Wells, an assistant professor of kinesiology at the University of Toronto, say it’s a problem when amateur sport organizations ban a substance but professional organizations still allow it.

He says all sports organizations need to present a consistent message and a consistent list of what is allowed and what’s not.

“I believe this speaks to the need for WADA… to get the professional sporting organizations to come online and get everybody adopt the same doping lists, because the lists are different for every organization,” he told CTV News Channel.