Calcium supplements can interfere with absorption of medications used to treat hypothyroidism.
Yes. Calcium supplements — or antacids containing calcium — can interfere with the absorption of thyroid hormone replacement medications, such as synthetic thyroid hormones levothyroxine (Synthroid, Unithroid, others) and liothyronine (Cytomel), as well as thyroid extract supplements.
This interference happens chiefly if you take thyroid hormone replacement and calcium supplements at or near the same time. You can avoid this problem with the following steps:
Other supplements — especially those containing iron — also can interfere with absorption of thyroid hormone replacement, as can certain foods and medications. If your doctor prescribes thyroid hormone replacement, be sure to tell him or her about all the other drugs and supplements you're taking.