The American sprinter Sha’Carri Richardson, who was set for a star turn at the Tokyo Olympics this month, could miss the Games after testing positive for marijuana.

Richardson, 21, won the women’s 100-meter race at the U.S. track and field trials in Oregon last month, but her positive test automatically invalidated her result in that marquee event.

The United States Anti-Doping Agency announced the positive test result Friday morning, and said Richardson had accepted a suspension of one month, starting on June 28. That could clear her in time to run in the 4×100 meter relay that takes place later in the Games — if she is named to the U.S. team.

In an interview with NBC on Friday, Richardson blamed the positive test on her use of marijuana as a way to cope with the unexpected death of her biological mother while she was in Oregon for the Olympic trials. Richardson, who was raised by her grandmother, said she learned about the death from a reporter during an interview and called it triggering and “definitely nerve-shocking.”

“It sent me into a state of emotional panic,” she said, adding, “I didn’t know how to control my emotions or deal with my emotions during that time.”

She apologized to her fans, her family and her sponsors, saying, “I greatly apologize if I let you guys down, and I did.”

U.S.A. Track & Field has notified other women who competed in the 100-meter final at the trials about the failed drug test, according to two people with direct knowledge of the information, and several runners have been told that they have moved up a spot in the final standings.

Jenna Prandini, who placed fourth at the trials, has been notified that she will now be one of the three American women running the 100 in Tokyo, and Gabby Thomas, who finished fifth at the trials, was named as an alternate for the race, the people said.

Richardson will be eligible to return to competition just before the track and field events at the Games begin on July 30. That day’s schedule includes the first qualifying rounds in the women’s 100, an event that now will happen without her.

Early Thursday afternoon, Richardson cryptically tweeted, “I am human.” And on NBC on Friday, she expanded on that thought.

“I just say, don’t judge me and I am human — I’m you, I just happen to run a little faster,” she said, adding that she expects some people to criticize her marijuana use. “They don’t necessarily understand, and I wouldn’t even call them haters.”

While Richardson’s suspension will be over by the time the Olympic track and field competition begins, the positive test erased her Olympic trials performance in the women’s 100, meaning she will not run in the event. Unlike the Olympic selection processes of some other countries, U.S.A. Track & Field’s procedures leave little room for discretion over who qualifies. They dictate that the top three finishers in a given event at the trials