American sprinter Sha'Carri Richardson has been ruled out of the Olympic Games after the 21-year-old gold medal hopeful tested positive for cannabis.

In a ruling described by US anti-doping chief Travis Tygart as "heartbreaking on many levels", it was confirmed that Richardson failed a test at the US Olympic trials on June 19.

Richardson's ban has been given a start date of June 28, when she was provisionally suspended, meaning she is ineligible to enter the Tokyo Games, which officially begin on July 23.

In a statement, the United States Anti-Doping Agency said: "USADA announced today that Sha'Carri Richardson, of Clermont, Fla., an athlete in the sport of track and field, has accepted a one-month suspension – as permitted under the applicable international rules – for an anti-doping rule violation for testing positive for a substance of abuse."

USADA chief executive Tygart said: "The rules are clear, but this is heartbreaking on many levels; hopefully, her acceptance of responsibility and apology will be an important example to us all that we can successfully overcome our regrettable decisions, despite the costly consequences of this one to her."

Richardson's ban means the second-fastest woman in the world over 100 metres this season will be absent from the Olympics.

She has run under 10.80 seconds three times in 2021, with a career personal best of 10.72secs set in Florida in April.

Only Jamaican veteran Shelly-Ann Fraser-Pryce has gone quicker this season, with a best of 10.63secs.

 Richardson was found to have THC, described by USADA as "the main psychoactive constituent of cannabis, marijuana, and hashish", above the urinary decision limit when she provided a test sample at the trials.

Given Richardson derived no sporting advantage and used the drug recreationally, she was given just a month-long ban. That was reduced from a possible three months because Richardson has "successfully completed a counselling programme regarding her use of cannabis", USADA said.

USA Track and Field (USATF) responded to news of the ban by describing the situation as a "devastating" blow.

In a statement, USATF said: "Sha'Carri Richardson's situation is incredibly unfortunate and devastating for everyone involved. Athlete health and well-being continue to be one of USATF's most critical priorities and we will work with Sha'Carri to ensure she has ample resources to overcome any mental health challenges now and in the future."