Many medications can interact with levothyroxine in harmful ways. It is especially important to avoid those in the "Important warnings" section of the label. These include the following medications, as well as others:
amiodarone (Nexterone, Pacerone)
androgens, such as nandrolone and testosterone (Androderm)
antacids containing aluminum or magnesium (Maalox, Mylanta)
beta-blockers, such as metoprolol (Lopressor), propranolol (Inderal, Innopran), or timolol
blood thinners, including heparin or warfarin (Coumadin, Jantoven)
carbamazepine (Carbatrol, Equetro, Tegretol, Teril)
corticosteroids, including dexamethasone
digoxin (Lanoxin)
methadone (Methadose)