US sports stars from Olympic track champion Michael Johnson to NFL and NBA stars backed Sha'Carri Richardson after she was suspended for using marijuana and lost her 100m Olympic berth.

The US Anti-Doping Agency (USADA) announced a one-month ban after she tested positive for marijuana, a banned World Anti-Doping Agency substance.

Richardson said she took the drug to cope with the pressure of trying to reach the Olympics and the pain of learning about the death of her biological mother.

"I don't know why marijuana is banned. Maybe a good reason. Maybe not," tweeted Johnson, a four-time world champion and two-time Olympic champion at 400m and former world and Olympic 200m champion.

"I know how it feels to lose a parent. Indescribable pain! I'm from the same neighborhood as (Richardson) Tough place! I wish people would stop calling her and this ban stupid unless you know the reason for both."

Kansas City Chiefs quarterback Patrick Mahomes, the 2020 Super Bowl Most Valuable Player, tweeted of Richardson's ban: "This is so trash man... just let her run!"

Richardson, who this season became the sixth-fastest woman ever at 100m, will not be able to compete in the event.

Sha'Carri Richardson, issued a one-month ban after testing positive for mariuana that will keep her from running the 100m at the Tokyo Olympics, received support from several top US sports figures, including Olympic and world 200 and 400 champion Michael
Sha'Carri Richardson, issued a one-month ban after testing positive for mariuana that will keep her from running the 100m at the Tokyo Olympics, received support from several top US sports figures, including Olympic and world 200 and 400 champion Michael Johnson. GETTY IMAGES NORTH AMERICA / Patrick Smith

Richard Sherman, a Super Bowl champion cornerback with Seattle, said he backed Richardson but questioned a society that would punish her for coping with personal loss.

"I'm very proud of this young woman but so frustrated at the place we are as a society," Sherman said.

"She is dealing with one of the greatest personal losses anyone could ever have to deal with in the midst of trying to accomplish one of the most difficult feats. Now we make her explain."

Retired NBA star Dwyane Wade addressed those who decided marijuana, legal in much of the United States, should be a banned substance.

"But majority of y'all rule makers smoke and probably are investors in THC companies," Wade said. "Let's stop playing these games."

The issue of Richardson's ban came up at the White House briefing and White House press secretary Jen Psaki noted it was a decision by USADA but stressed: "Sha'Carri Richardson is an inspiring young woman who has gone through a lot personally.

"And she also happens to be one of the fastest women in the world and that's an important part of the story as well."