What Should I Tell My Healthcare Provider?You should talk with your healthcare provider prior to taking levothyroxine if you have:
- Any heart problems
- An overactive thyroid (hyperthyroidism)
- A recent history of heart attack
- Adrenal insufficiency
- Any allergies, including allergies to food, dyes, or preservatives.
Also, let your healthcare provider know if you are:
- Pregnant or thinking of becoming pregnant (see Levothyroxine and Pregnancy)
- Breastfeeding (see Levothyroxine and Breastfeeding).
Make sure to tell your healthcare provider about any other medicines you are taking, including prescription and non-prescription medicines, vitamins, and herbal supplements.
(Click Precautions and Warnings With Levothyroxine to learn more, including information on who should not take the drug.)
How Does Levothyroxine Work?The thyroid gland makes two similar (although slightly different) thyroid hormones: triiodothyronine (T3) and levothyroxine (T4). Usually, the thyroid gland produces much more T4 than T3 (however, T3 is much more active in the body than T4). The body can convert the T4 hormone into the T3 hormone as necessary. If your thyroid does not make enough thyroid hormones, there are a few different ways to increase your levels.
Some forms of thyroid replacement combine both T3 and T4 (such as natural thyroid replacement made from pig thyroids). However, because the body converts T4 into T3 as needed, most people can successfully take just T4 (such as levothyroxine). This is the most common type of thyroid replacement. Another option includes taking just T3 hormones (such as Cytomel®).
Although it is synthetic, levothyroxine is identical to the naturally occurring hormone T4.