Caster Semenya has lost her landmark legal case against her sport’s ruling body, meaning she will be forced to take medication to reduce her testosterone levels if she wants to carry on competing. The South African is one of the most dominant stars of modern track and field—she’s a double Olympic 800-meter gold medalist and three-time world champion. Her gender, and possible advantages owned to her naturally higher testosterone levels, have come under intense scrutiny. The Court of Arbitration for Sport made its surprise decision early Wednesday, and it’s likely to significantly damage the rest of Semenya’s running career. However, the court did say it had serious concerns over proposed new rules for athletes with differences in sexual development.