Maria Sharapova during her quarterfinal match at the Australian Open tennis tournament in January. A drug test Sharapova took during the event later came back positive for the banned substance meldonium. Rick Rycroft/AP hide caption

Russian tennis star Maria Sharapova isn't competing at the 2016 Olympics. At a March 7 press conference in Los Angeles, she told reporters she'd tested positive for meldonium, a prescription heart drug that improves blood flow. It was banned in January by the World Anti-Doping Agency. Robyn Beck/AFP/Getty Images hide caption

Russian Olympians, along with coaches and other officials, pose outside the Assumption Cathedral in Moscow on Wednesday before heading to Brazil. Russia had planned to send nearly 400 athletes to the Rio Games, but more than 110 have been banned because of a doping scandal. Alexander Zemlianichenko/AP hide caption

Runners compete in the marathon at the 2012 Paralympics in London. The International Paralympic Committee said Friday it is investigating reports of widespread doping among Russia's disabled athletes and is considering banning the entire Russian team from the Paralympics in Brazil in September. Emilio Morenatti/AP hide caption

New analysis of stored samples taken from athletes at the Beijing and London Summer Olympics has turned up 45 cases of banned substances. Here, urine samples are recorded upon arriving at the China Anti-Doping Agency in Beijing in 2008. Robert F. Bukaty/AP hide caption

Russian athletes compete at track and field championships in Cheboksary on June 20. The International Olympic Committee has banned Russia's track and field team from the Summer Games for pervasive doping violations. The IOC on Tuesday put off a final decision on whether to bar the entire Russian team from the games that begin in Brazil on Aug. 5. Francesca Ebel/AP hide caption

Canadian law professor Richard McLaren speaks at a news conference Monday in Toronto. McLaren is the author of a new report that accuses Russia of a widespread doping campaign. Frank Gunn/AP hide caption

Justin Gatlin celebrates victory in the 100 meters at the U.S. Olympic Trials for track and field. Gatlin has been suspended twice for failing doping tests, once in 2001 and again in 2006. Andy Lyons/Getty Images hide caption

Cyclists in this year's Tour de France will face new controls for what organizers call "technological fraud." Here, elite cyclists are seen riding in the Paris-Nice race in March. Kenzo Tribouillard/AFP/Getty Images hide caption

A major doping crackdown dating back to 2008 could result in 31 athletes being barred from competing in the 2016 Rio Olympics. Felipe Dana/AP hide caption

Bribes paid by runner Liliya Shobukhova are at the center of an ethics inquiry, according to the IAAF, track and field's governing body. Ben Stansall/AFP/Getty Images hide caption

Russia's Mariya Savinova won gold in the 800-meter final at the 2012 Olympics in London. A new report ruled that she should never should have competed because her drug test profile showed she was doping. Matt Dunham/AP hide caption

Participants play the latest video games at the gamescom computer game fair in Cologne, Germany, on Wednesday. The Electronic Sports League, which sponsors a tournament in the city later this month, says it will require random drug tests to ensure players are clean. Martin Meissner/AP hide caption