How the interaction occurs:
Calcium carbonate decreases the amount of levothyroxine your body absorbs.
What might happen:
Your levothyroxine may not work as well.
What you should do about this interaction:
Let your healthcare professionals (e.g. doctor or pharmacist) know that you are taking these medicines together. Your doctor may want to check you thyroid function test to see if you are getting the right amount of levothyroxine. Your doctor may want you to take your levothyroxine and calcium carbonate at different times of the day.Your healthcare professionals may already be aware of this interaction and may be monitoring you for it. Do not start, stop, or change the dosage of any medicine before checking with them first.
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2.Schneyer CR. Calcium carbonate and reduction of levothyroxine efficacy. JAMA 1998 Mar 11;279(10):750.
3.Phansalkar S, van der Sijs H, Tucker AD, Desai AA, Bell DS, Teich JM, Middleton B, Bates DW. Drug-drug interactions that should be non-interruptive in order to reduce alert fatigue in electronic health records. J Am Med Inform Assoc 2012 Sep 25.