Synthroid is a man-made form of thyroxine, which is one of the two hormones produced by the thyroid gland. A person with an underactive thyroid gland or hypothyroidism takes a daily dose of Synthroid as replacement therapy. The drug is also used to treat thyroid conditions such as goiter and thyroid cancer. Adequate levels of thyroid hormones in the bloodstream are important to maintain normal mental and physical health. Certain drugs, mineral supplements and foods affect the absorption and can change the therapeutic response to Synthroid.
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Interaction with Calcium Carbonate
Synthroid comes in tablet form and is usually taken once a day on an empty stomach, preferably a half hour to one hour before breakfast. If you are taking a calcium supplement to prevent bone loss or an antacid that contains calcium carbonate, take it at least four hours before or four hours after taking Synthroid. Preparations that contain calcium carbonate, as well as aluminum, magnesium, ferrous sulfate and simethicone, may, when taken concurrently with Synthroid, reduce its efficiency. Calcium carbonate may form an insoluble chemical compound with Synthroid. This causes binding and the prevention of or delayed absorption, potentially resulting in hypothyroidism.
Too much dietary fiber can interfere with the absorption of synthetic thyroid hormone. You should avoid taking Synthroid at the same time with walnuts, soybean flour, cottonseed meal and foods that are high in fiber. Dietary fiber may bind and decrease the absorption of Synthroid in the gastrointestinal tract. RxList.com says that the effect on absorption caused by consuming these types of foods may necessitate adjustments in dosing.
Dairy products such as milk, yogurt and cheese are rich sources of calcium. Leafy green vegetables like kale, spinach and collard greens are high in both fiber and calcium. Calcium is an important mineral for maintaining healthy bones and teeth, as well as for normal blood-clotting and heart and nerve function. You would not want to eliminate calcium, nor dietary fiber, from your diet completely while taking a synthetic thyroid hormone. Before starting Synthroid, talk to your doctor about dietary restrictions and guidelines.
The Bottom Line
Take Synthroid on an empty stomach for maximum absorption. Do not take a calcium supplement within four hours of taking Synthroid. Consult your doctor about dietary restrictions of high-fiber foods and foods containing calcium.