A U.S. Olympic source told NBC News that Richardson failed a drug test following her victory at the U.S. Olympic Track and Field Trials in Eugene, Oregon, on June 19. Richardson, 21, is now prohibited from competing in the 100-meter race, but could possibly compete in another event. THC is banned during competition, according to the World Anti-Doping Agency. It is unclear if she will appeal the drug test results. Richardson on Thursday tweeted, "I am human."