5
Table 3. Common Physiological and Pharmacological Effects
on the Biology of the Thyroid Hormone Axis
Cause Drug Effect
Inhibit TSH
secretion
Dopamine, L-dopa; glucocorticoids;
somatostatin
f T4; f T3; TT4;
TT3; TSH
Inhibit thyroid
hormone (TH)
synthesis or release
Iodine, lithium; 6-n-propyl-2-thiouracil,
methimazole
f T4; f T3;
TT4; TT3;
TSH
Inhibit conversion
of T4 to T3
Amiodarone, glucocorticoids,
propranolol, propylthiouracil;
radiographic contrast agents
TT3; f T3; rT3;
, ⇋, T4 and f T4;
⇋, TSH
Inhibit binding of
T4/T3 to serum
proteins
Salicylates, phenytoin, carbamazepine,
furosemide, NSAIDs; heparin (in vitro
effect)
TT4; TT3; ⇋,
f T4; ⇋, f T3;
⇋TSH
Stimulate
metabolism of
iodothyronines
Phenobarbital, phenytoin, carbamazepine,
rifampicin
yroid axis should
correct in euthyroid,
requirement increase in
hypothyroidism
Inhibit absorption
of ingested T4
Aluminum hydroxide, ferrous sulfate,
calcium salts, antacids, proton pump
inhibitors, cholestyramine, colestipol;
sucralfate, soybean preparations,
kayexalate
TT4; f T4;
TSH (in
hypothyroidism)
Increase in
concentration of
T4-binding proteins
Estrogen, clofibrate; opiates (heroin,
methadone), 5-fluorouracil; perphenazine
TT4; TT3;
⇋f T4; ⇋TSH
Decrease in
concentration of
T4-binding proteins
Androgens, glucocorticoids
TT4; TT3;
⇋f T4; ⇋TSH
Adapted from Tietz Textbook of Laboratory Medicine Seventh Edition ISBN 9780323775724.
