Calcium Supplements Interfere with Thyroid treatment

Calcium supplements — or antacids containing calcium — can interfere with the absorption of levothyroxine (Synthroid, Unithroid, others), a synthetic form of thyroid hormone.

This interference happens chiefly if you take levothyroxine 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 levothyroxine.
Take any products containing calcium at least four hours before or after taking levothyroxine.
Other supplements — especially those containing iron — also can interfere with absorption of levothyroxine, as can certain foods and medications. If your doctor prescribes levothyroxine, be sure to tell him or her about all the other drugs and supplements you're taking.