Russian figure skater Kamila Valieva gets to compete after a failed drug test. Sha'Carri Richardson wants to know why she was treated differently.

U.S. track star Sha'Carri Richardson, who missed out on the Olympics last year after testing positive for marijuana, is calling out what she believes to be a racial bias when it comes to drug testing in sports. It was revealed this week that Russian figure skater Kamila Valieva failed a drug test ahead of the Winter Olympics in Beijing –  but has been cleared to compete.

"Can we get a solid answer on the difference of her situation and mines?" Richardson tweeted on Monday. "My mother died and I can't run and was also favored to place top 3. The only difference I see is I'm a black young lady."

Richardson, 21, who was disqualified from the women's 100 meters following her Olympic qualifying run last July, said during an interview with NBC News that she used marijuana in Oregon – where the substance is legal – to cope with the death of her mother. She said she wasn't making excuses and took responsibility for her actions. 

She was suspended for one month, and coaches chose not to add her to the Olympic roster in an effort to "maintain fairness" for the other athletes who adhered to the banned substances rules, USA Track and Field said.

In Valieva's case, the skater tested positive for a banned heart medication, trimetazidine, in Russia in December. The drug – used to treat heart-related conditions, but not approved in the U.S. – increases blood flow to the heart, according to Reuters.

"If you're in a highly exertional sport, where you're using a lot of energy and you're putting your heart under significant stress, it certainly could help your heart function better theoretically," Dr. Kelly Johnson-Arbor, a medical toxicology physician at MedStar Georgetown University Hospital, told Reuters.

A hastily arranged hearing on the 15-year-old's failed drug test ended in less than 12 hours, with the Court of Arbitration for Sport ruling on Monday she does not need to be suspended ahead of an investigation into the test. The court said its decision favored her because she was a minor or "protected person," and was subject to different rules from an adult athlete.

Valieva, the favorite for the women's individual gold, can keep skating before her case is resolved but the ruling doesn't decide the fate of the one gold medal that she has already won in Beijing. If she does place in the top three, there won't be a medal ceremony,  the International Olympic Committee said.

"It's all in the skin," Richardson wrote in another tweet on Monday, referring to what she believes to be a racial bias. She pointed out that THC, a chemical found in marijuana, is not a performance-enhancing drug.

"Failed in December and the world just now know however my resulted [sic] was posted within a week and my name & talent was slaughtered to the people," she said in another tweet, pointing out how Valieva's failed test occurred months before the competition, but wasn't questioned until this week.

Other athletes have questioned random drug testing in sports, including tennis superstar Serena Williams. In 2018, Williams said she, out of all tennis players, receives the most random drug tests – calling into question how random they actually were. "Discrimination? I think so. At least I'll be keeping the sport clean," she tweeted.

By June 2018, Williams had been tested five times, whereas many of her peers had been tested one, two or zero times, according to a U.S. Anti-Doping Agency database, CBS Sports reports.

The U.S. has a history with racial bias when it comes to policing marijuana use. Marijuana use is roughly equal among Black and white Americans, yet Black people are 3.73 times as likely to be arrested for marijuana possession, according to a report by the American Civil Liberties Union.

In sports, marijuana is widely prohibited. The World Anti-Doping Agency said in a statement that it is reviewing cannabis' status as a banned substance, which was prompted after the agency received requests from "a number of stakeholders." The announcement came two months after Richardson's high-profile disqualification due to marijuana. 

The scientific review of cannabis by the agency's advisory group will be initiated in 2022, the agency said. 

While cannabis is legal or decriminalized in dozens of states, the U.S. Drug Enforcement Administration lists the substance as a Schedule I drug, putting it in the same category as cocaine and heroin. 

However, some people – including athletes – use it for its therapeutic properties, including MMA fighter Elias Theodorou, who uses it to treat bilateral neuropathy, a result of damage to the nerves located outside of the brain and spinal cord. He became the first professional athlete to gain a medical marijuana exemption from a state athletic commission inside the United States in May 2021.