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:

• Don't take calcium supplements or antacids at the same time you take thyroid hormone replacement.
• Take any products containing calcium at least four hours before or after taking thyroid hormone replacement.

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.