No, it's not what Iron Man's new armor is made of. But it does make you stronger.

Meldonium is the banned substance that tennis star Maria Sharapova just admitted taking. She claims she'd been taking it for health reasons for 10 years before it was banned. She says she took it because she was regularly falling ill. She also says she had a magnesium deficiency and a family history of diabetes.

But the World Anti-Doping Agency says athletes like her take it to perform at an extreme level. 

Sharapova is now facing a four-year ban. But she's hardly the only athlete to take Meldonium. The Guardian compiled a list of athletes who tested positive for it. That includes Abebe Aregawi, the 2013 women’s 1,500m world champion; Endeshaw Negesse, the 2015 Tokyo marathon champion; Olga Abramova and Artem Tyschcenko, two Ukrainian biathletes; Eduard Vorganov, a Russian cyclist; and Ekaterina Bobrova, a Russian ice dancer.

WADA monitored the drug before placing it on the banned substance list. Athletes were given a heads-up about it. But Sharapova says she didn't bother reading it. “I received a letter on Dec. 22 from WADA, an email with changes happening for next year as well as reporting your whereabouts and a link to a button where you can press to see the prohibited items for 2016,” she said in a press conference. “I did not look at that list.”

Her sponsors aren't so supportive. Nike suspended its sponsorship saying it was "saddened and surprised." Tag Heuer cut ties with her completely. And Porsche is "postponing planned activities" with her. In 2015, Sharapova earned more than $30 million. She'll be fine. But it's a costly mistake.

The error might be due to the widespread use of Meldonium in former Soviet countries. Latvian professor Ivars Kalvins invented it more than three decades ago. The professor is rightly proud of the drug. "It's saved millions of lives in former USSR countries," he says.

Kalvins is also very defensive about athletes taking it. "If you look at how sportsmen do their training, they’re working very hard and close to the border of maximum acceptance level of load," he says. "That means, if they go over this, then the heart will be damaged. Immediately. So sportsmen will use Meldonium to protect themselves."

This happens during training or during sports events. "But if they apply this protection, then they are safe. It can protect them from dying," says Kalvins.

While he's not a big fan of tennis, he certainly knows the name Maria Sharapova. She's a huge star in the region. And Kalvins is upset that she might be punished for taking his drug. "It’s unbelievable that such a stupid decision was made by the committee to stop use of Meldonium," he says. "It’s against human rights. The sportsman is also a human being who should have the same rights as everyone else."

From PRI's The World ©2015 Public Radio International