Table 1.

Changes in thyroid function tests occurring in euthyroid amiodarone-treated subjects

Assay	Short-term therapy	Underpinning mechanism(s)	Long-term therapy	Underpinning mechanism(s)
Thyrotropin	Increased	Decreased T4 production (Wolff-Chaikoff effect) (major contribution) Inhibition of pituitary D2 activity (minor contribution) Inhibition of T3 binding to its pituitary receptor (minor contribution)	Normal	Normalized T4 production (escape from the Wolff-Chaikoff effect)
Thyroxine (T4): total (TT4) and free (FT4)	Increased	Inhibition of hepatic D1 activity	Slightly increased/high normal	Inhibition of hepatic D1 activity Increased T4 production rate Decreased T4 metabolic clearance rate
Triiodothyronine: total (TT3) and free (FT3)	Decreased	Inhibition of hepatic D1 activity	Slightly decreased/low normal	Inhibition of hepatic D1 activity Increased T4 production rate Decreased T4 metabolic clearance rate
Reverse T3	Increased	Inhibition of hepatic D1 activity	Increased	Inhibition of hepatic D1 activity

D1, type 1 iodothyronine deiodinase; D2, type 2 iodothyronine deiodinase.