The thyroid medication levothyroxine (LEVO-T, LEVOXYL, NOVOTHYROX, SYNTHROID, THYRO-TABS, UNITHROID) is used to treat hypothyroidism, an endocrine disorder resulting from a thyroid homone deficiency that affects about 4.6 percent of the U.S. population. The medication is used to replace the missing or deficient amount of thyroid hormone. The number of prescriptions for levothyroxine filled each year—more than 75 million U.S. prescriptions in 2007 — makes it one of the most prescribed drugs in the country.
Unfortunately, the use of other medications while taking levothyroxine could have one of several kinds of unintended results:
• Certain medications can decrease the absorption of levothyroxine resulting in lower levels in the blood.
• Other medications can increase the rate at which the body gets rid of levothyroxine, also resulting in lower thyroid levels in the blood.
• Other medications can cause changes of levothyroxine binding in blood
• Levothyroxine can affect the safety or effectiveness of other medications by raising or lowering the levels of these other drugs in the blood.