Drugs that interact with thyroid medications

Hypothyroidism is usually treated with a daily dose of synthetic T4 (levothyroxine sodium) in pill form. Once the right dose is established, your TSH will be checked every six months or so.

Taking a daily pill is simple, but you need to be aware of some possible interactions—for example, antacids and supplemental iron can interfere with thyroid hormone absorption and should be taken at a different time. Below is a list of medicines and therapies that can interact to greater and lesser degrees with your thyroid medication.

Drugs that may interact with thyroid medicine

The following medicines and therapies can influence the effectiveness of thyroid medicines in one or more of the following ways: by interfering with the absorption of thyroid hormone, by binding thyroid hormone to binding proteins, and by interfering with thyroid hormone metabolism.

Cancer therapies

Gastrointestinal therapies

Nutritional supplements







aluminum hydroxide antacids

cation exchange resins



calcium carbonate

ferrous sulfate (iron)

iodine* (including kelp supplements)

multivitamins (presumably because of iron and calcium content)


Cardiovascular therapies

Hormone therapies

Other medicines




oral anticoagulants

androgens/anabolic steroids

dopaminergic drugs including bromocriptine and cabergoline


glucocorticoids such as prednisone

growth hormone

antituberculous (rifampicin, ethionamide)

nonsteroidal anti-inflammatory drugs (NSAIDs) such as meclofenamic acid, mefenamic acid, phenylbutazone

orphenadrine (Norflex, Norgesic)

propranolol (Inderal)

radiographic agents (such as contrast agents

containing iodine in addition to ipodate* and iopanoic acid*)

salicylates (high doses of aspirin and salsalate)

slow-release niacin (cholesterol-lowering drug)

sulfonamides (acetazolamide, sulfisoxazole)


Cholesterol therapies

Cholesterol therapies

bile acid sequestrants

including cholestyramine*, colestipol*, and clofibrate

anticonvulsants including phenytoin*, phenobarbital*, and carbamazepine*



other antidepressants and antipsychotic agents including quetiapine, clomipramine, and methadone

* These drugs can have a major impact on thyroid treatment.

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