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In April 2018, the IAAF announced new "differences of sex development" rules that required athletes with specific disorders of sex development, testosterone levels of 5 nmol/L and above, and certain androgen sensitivity to take medication to lower their testosterone levels, effective beginning 8 May 2019. Due to the narrow scope of the changes, which also apply to only those athletes competing in the 400m, 800m, and 1500m, many people thought the rule change was designed specifically to target Semenya."
-- https://en.wikipedia.org/wiki/Caster_Semenya#2018_testostero...