Thyroid Hormone Abuse Among Elite Athletes

CONTEXT: Thyroid hormone (TH) abuse for performance enhancement in sport remains controversial and it is not prohibited in sports under the World Anti-Doping Code. However, the prevalence of TH usage in athletes is not known. OBJECTIVE: We investigated TH use among Australian athletes undergoing antidoping tests for competition in World Anti-Doping Agency (WADA)–compliant sports by measuring TH in serum and surveying mandatory doping control form (DCF) declarations by athletes of all drugs used in the week prior to the antidoping test. METHODS: Serum thyroxine (T4), triiodothyronine (T3), and reverse T3 were measured by liquid chromatography–mass spectrometry and serum thyrotropin, free T4, and free T3 by immunoassays in 498 frozen serum samples from antidoping tests together with a separate set of 509 DCFs. RESULTS: Two athletes had biochemical thyrotoxicosis giving a prevalence of 4 per 1000 athletes (upper 95% confidence limit [CL] 16). Similarly, only 2 of 509 DCFs declared usage of T4 and none for T3, also giving a prevalence of 4 (upper 95% CL 16) per 1000 athletes. These estimates were consistent with DCF analyses from international competitions and lower than the estimated T4 prescription rates in the age-matched Australian population. CONCLUSION: There is minimal evidence for TH abuse among Australian athletes being tested for competing in WADA-compliant sports.