The influence of drugs on thyroid function

There are numerous commonly used substances which can affect the central control, synthesis and peripheral effects of thyroid hormones. Question 25 from the second paper of 2013 asks specifically for the effects of amiodarone, propranolol, glucocorticoids and opiates. Those either inhibition the peripheral conversion T4 to T3 (first two) or inhibit TSH secretion (second two). But there are many other thyroid-influencing drugs.

This is an attempt to create a referenced list of such substances, ordered according to their effect on thyroid function.

Drugs Which Affect Thyroid Function
~Organised by Their Effect on Thyroid Hormones~
TSH Inhibition of release






Stimulation of release


Antipsychotics, especially amisulpiride

T3 and T4 synthesis Inhibition of thyroid synthetic function

Thiouracils (eg. propylthiouracil)

Imidazoles (eg. carbimazole)

Lithium carbonate



Stimulation of thyroid synthetic function

Inorganic iodine (eg. potassium iodide) - if you have a normal thyroid gland

Iodinated contrast agents (high iodine content)


T3 and T4 release from the thyroid gland Inhibition of release

Inorganic Iodine (eg. potassium iodide)

Iodinated contrast agents (high iodine content)

Stimulation of release

Amiodarone (by thyroiditis)

Conversion of T4 into T3 Inhibition of conversion




Thiouracils (eg. propylthiouracil)

Stimulation of conversion


Selenium (a cofactor in T4-T3 conversion; selenium supplementation will not result in a supranormal T3 level - merely a return to normal)

Transport of thyroid hormones by binding to thyroid-binding globulin (TBG)

Increased TBG levels

(thus decreased free T3)



5-fluorouracil (5-FU)



Decreased TBG levels

(thus increased free T3)

Androgen hormones


Niacin (nicotinic acid)

Increased binding of T4 to TBG

Estrogens, particularly in the setting of pregnancy

Decreased binding of T4 to TBG (by displacement)

Aspirin and salicylates in general

Frusemide (and ethacrynic acid)


Clearance of T4 Increased clearance





Decreased clearance


Glycosylflavones in millet-rich diets of the poor in the developing world, or in the weird hippies who think it is healthy to emulate them.

The same table, reorganised to reflect the difference in the clinical picture arising from exposure to these drugs:



Drugs Which Affect Thyroid Function
~Organised by Their Clinical Effect on Thyroid Function~


As always, good old UpToDate has a summary of this topic, which is both detailed and concise. There is even a nice table of drugs which cause changes in TFTs.

For the freegan, Life In The Fast Lane have a characteristically brilliant summary of drugs which affect thyroid function.

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