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Caster Semenya won the World Championships in the women's 800 metres in 2009, 2011, and 2017. She is a South African athlete who has been the subject of controversy due to her high testosterone levels. In 2011, the International Association of Athletics Federations (IAAF) introduced new regulations that required female athletes with high testosterone levels to take medication to reduce their testosterone levels in order to compete in women's events.