Table 2. Drugs that affect thyroid function in patients taking levothyroxine. Mechanism of action in italics.

Inhibition of levothyroxine absorption

Iron

Calcium

Aluminum hydroxide

Colestyramine

Colestipol

Sucralfate

Raloxifene

Increased hepatic metabolism

Phenobarbitol

Phenytoin

Carbemazepine

Rifampin

TKI (Imatinib, axitinib, motesanib, vandetanib)

Rexinoids

Decrease hepatic metabolism

Metformin?

Inhibition of 5’ deiodinase

Propylthiouracil

Methimazole

Propranolol

Glucocorticoids

Iodide

Increased thyroxine binding globulin levels

Estrogen

Raloxifene

Tamoxifen

Methadone

Mitotane

Fluorouracil

Decreased thyroxine binding globulin levels

Androgens

Glucocorticoids

Nicotinic acid

TKI - tyrosine kinase inhibitors

^?- not verified by multiple studies/investigators