Levothyroxine absorption can be reduced by which of the following?

• A. Calcium and iron supplements taken around the same time as levothyroxine
• B. Certain foods eaten with it
• C. Taking it in the evening rather than the morning
• D. All of the above

Answer: (D)

Levothyroxine absorption works best when the drug is in the stomach on an empty stomach, free from substances that can bind it or slow gastric emptying. Calcium and iron supplements, if taken near the same time, can bind the hormone in the gut and markedly reduce how much is absorbed. Some foods eaten with the medication can also interfere by binding the hormone or delaying its absorption. Taking the medication in the evening rather than the morning can reduce absorption as well, because meals and different eating patterns later in the day can disrupt the fasting state that promotes optimal uptake. Since each of these scenarios can lower absorption, all of the above is the best answer.