Sha'Carri Richardson not selected for USA women's 4x100m relay team at Tokyo Olympics after positive cannabis test

American sprinter Sha'Carri Richardson will miss the Tokyo Olympics after she was not selected for the USA's 4x100m relay team following her one-month ban for testing positive for cannabis.

The 21-year-old won the 100m at the US Olympic trials in June and was expected to be one of the biggest draws at the upcoming Tokyo Games.

Richardson's positive test came at the Olympic trials event in Oregon and her suspension - which began on June 28 - finishes before Tokyo's track and field programme begins on July 30.

But her results at the trials have been wiped out and the United States Anti-Doping Agency had said her eligibility for the Games would be a decision for US Track and Field (USATF) and the US Olympic and Paralympic Committee.

"We are incredibly sympathetic toward Sha'Carri Richardson's extenuating circumstances and strongly applaud her accountability - and will offer her our continued support both on and off the track," USATF said in a statement.

Richardson said in an NBC interview last week that she used the banned substance to cope with the death of her mother.

She was regarded as one of the favourites for a gold medal in the 100m, having run the sixth-fastest time in history this year.

The USTF added: "All USATF athletes are equally aware of and must adhere to the current anti-doping code, and our credibility as the National Governing Body would be lost if rules were only enforced under certain circumstances."

The organisation said it believes the World Anti-Doping Agency rules regarding tetrahydrocannabinol, the main psychoactive constituent of cannabis, "would be re-evaluated".

"While our heartfelt understanding lies with ShaCarri, we must also maintain fairness for all of the athletes who attempted to realise their dreams by securing a place on the US Olympic Track & Field Team," it said.