By Derek Wilson

Colorado Springs, Colorado - US sprinter Sha’Carri Richardson has been ruled out of the Olympic Games in Tokyo with a one-month doping ban after testing positive for a by-product of cannabis at the US trials in June.

Richardson (21) qualified for the Games after winning the 100 meter final at the trials in 10.86 seconds, a spectacular time which confirmed her status as a contender for gold.

But the positive sample saw her disqualified from the event and ineligible for the Games, which begin later this month.

"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," said US anti-doping agency (USADA) chief Travis Tygart.

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Cannabis is prohibited in competition and in the World Anti-Doping Code USADA said it was classified as a “substance of abuse” because of its use in society outside sport.

"I am human," Richardson posted on Twitter on Thursday. Her name had been withdrawn from the Diamond League entry lists for Stockholm on Sunday and she hadn't competed since the 100m trials finals, having not contested the later 200m.

A three-month ban is customary for transgressions, but this can be reduced to one-month if the athlete in questions takes an approved treatment program, as Richardson will in this case.