U.S. champion sprinter Sha'Carri Richardson can't compete in Olympics because she tested positive for THC

USA Track and Field gave 100-meter dash star Sha'Carri Richardson a 30-day suspension, effectively banning her from participating in the Olympics. The 21-year-old athlete, who won the Olympic trials on June 19 with a time of 10.86 seconds, said she smoked pot to help her cope with the death of her mother.

From AP:

After the London Olympics, international regulators relaxed the threshold for what constitutes a positive test for marijuana from 15 nanograms per milliliter to 150 ng/m. They explained the new threshold was an attempt to ensure that in-competition use is detected and not use during the days and weeks before competition.

Though there have been wide-ranging debates about whether marijuana should be considered a performance-enhancing drug, the U.S. Anti-Doping Agency makes clear on its website that "all synthetic and naturally occurring cannabinoids are prohibited in-competition, except for cannabidiol (CBD)," a byproduct that is being explored for possible medical benefits.