American sprint star Sha'Carri Richardson is out of the 100 metres at the Tokyo Olympics after her trials success was wiped out following a positive test for a substance of abuse.

The United States Anti-Doping Agency (USADA) announced on Friday that the 21-year-old had been suspended for one month after testing positive on June 19 for THC, the main psychoactive constituent in cannabis. The sample was provided on the day of her win at the trials.

As part of the sanction, that result at the US Olympic Trials has been disqualified. The US bases qualification for the Games solely on trials performance, meaning Richardson is out.

However, the fact the ban is only one month and that discretionary places can be awarded for the 4x100m relay means there is still a chance she could compete in that event.

Richardson has posted the second-fastest 100m time in the world this year, running the distance in 10.72 seconds in April. Her time in winning the US trials was 10.86secs.

USADA chief executive Travis Tygart said: "The rules are clear, but this is heart-breaking 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."

USADA said the period of ineligibility had been reduced to one month, starting from June 28.

The ban was reduced from the usual three-month period because her use of cannabis occurred out of competition, was unrelated to her sport performance and because she completed a counselling programme in relation to the drug use, USADA said.

USADA said it was up to the United States Olympic and Paralympic Committee (USOPC) and USA Track and Field (USATF) to determine her eligibility for the Tokyo Games.

USOPC said: "While we are heartbroken, the USOPC is steadfast in its commitment to clean competition and it supports the anti-doping code.

"A positive test for any banned substance comes with consequences and we are working with USATF to determine the appropriate next steps. We are dedicated to providing Sha'Carri the support services she needs during this difficult time."

USATF's statement read: "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."

Richardson said she used cannabis after learning about the death of her biological mother from a reporter while preparing for the trials. Smoking cannabis is legal in Oregon, where the trials took place.

"That (news) sent me in a state of mind of emotional panic," she told NBC's Today programme.

"I was just blinded by emotion and hurt. I know I can't hide myself, so I tried to hide my pain."

Asked about the possibility of competing in the relay, Richardson said: "Right now I'm just putting all of time and my energy into dealing with what I need to deal with to heal myself.

"If I am allowed to receive that blessing then I am grateful for it, but if not, right now I am just going to focus on myself."

Richardson apologised to her family, her fans and her sponsors for not knowing how to control her emotions.

"I'm human, I'm you, I just happen to run a little faster."