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.
Keywords: athlete; doping; thyroid hormone.
© The Author(s) 2023. Published by Oxford University Press on behalf of the Endocrine Society.