What are the risks of taking Synthroid (levothyroxine)?

What should I tell my doctor before starting Synthroid (levothyroxine)?

Tell your doctor if you are allergic to levothyroxine, thyroid supplements, any other medications, or any of the active or inactive ingredients in Synthroid tablets and capsules. Your pharmacy can provide you with a list of ingredients.

Give your doctor a complete list of your prescription and over-the-counter medications, including vitamins, nutritional supplements, and herbal products. This can help avoid serious drug interactions. 

Tell your doctor about all your medical conditions. In particular, mention if you have adrenal insufficiency (a condition in which the adrenal glands do not produce enough adrenal hormones). If you have this condition, your doctor may decide Synthroid is not right for you. 

 Also, tell your doctor if you have ever had diabetes, atherosclerosis (hardening of the arteries), anemia, bleeding problems, osteoporosis (weak or brittle bones), pituitary gland problems, porphyria, kidney disease, liver disease, or heart disease. Also, inform your doctor if you have recently undergone radiation therapy. 

Women who are pregnant, could be pregnant, plan to become pregnant, or are breastfeeding should tell their doctor before starting Synthroid treatment. 

What precautions should I take while on Synthroid (levothyroxine)?

Keep all your healthcare appointments while on Synthroid treatment. Your doctor will check thyroid levels and make dose adjustments. They will also monitor you carefully for Synthroid side effects.

Certain foods and beverages can affect how Synthroid works, particularly foods containing walnuts, soybeans, dietary fiber, grapefruit, and drinking grapefruit juice. Talk to your doctor before eating or drinking these foods and beverages.

 If you take ferrous sulfate (iron supplement) or calcium carbonate (Tums), be sure to take them at least 4 hours away (before or after) your Synthroid dose. Likewise, if you take certain cholesterol-lowering medications like colesevelam (Welchol), cholestyramine (Prevalite), colestipol (Colestid), or certain other medications like sevelamer (Renvela, Renagel) or sodium polystyrene sulfonate (Kayexalate), take these medicines at least 4 hours after Synthroid.

If you become pregnant while taking Synthroid, call your doctor. Your dose of Synthroid may need to be increased.

If you have surgery, including dental surgery, while on Synthroid treatment, tell the doctor or dentist that you are taking this medication.

What are Synthroid (levothyroxine) interactions?

Taking Synthroid with certain other medications can affect how well this medicine works. Drug interactions can also increase the risk of serious adverse effects. Your physician may choose a different medication for hypothyroidism, change the dose or frequency of your medicines, and/or monitor you carefully for side effects if there are known interactions between Synthroid and any of your other medicines. 

There can be drug interactions between Synthroid and the following medications:

This is not a complete list of Synthroid drug interactions. Many other medications may also interact with Synthroid. Be sure to tell your doctor about all the medications you are taking or plan to take, even if they do not appear on this list.