Link between Estrogen and Levothyroxin

Can anyone please point me towards any research relating to interactions with estrogen and levothyroxin, especially absorbtion. I have trawled the web but have found very little. I am on evorell hrt and 50 mcg levo, reduced to this dose as my bloods are too high for the 75mcg I was orginally on. However, after 10 days on the reduction, my hands and feet are freezing and I have got ill (not had a virus for about a year - coincidence?). I am particulary interested with thyroid binding globulin, which I have read is in the estrogen and ensures that the thryoxin goes into the blood but does not get the vital organs. I would very much like to get some solid and recent research to give to my doctor, in the hope that I can get my much needed additional 25mcg back, or change to a treatment which works with my hrt. All information gladly received. Many thanks.

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  • The following excerpt is from the patient information leaflet for Thyrolar, which is a US brand of thyroid medication. (The fact that it's a US brand is of course irrelevant - it's just that their patient info leaflets are so much more comprehensive than ours)

    "Estrogen, Oral Contraceptives—Estrogens tend to increase serum thyroxine-binding globulin (TBg). In a patient with a nonfunctioning thyroid gland who is receiving thyroid replacement therapy, free levothyroxine may be decreased when estrogens are started, thus increasing thyroid requirements. However, if the patient's thyroid gland has sufficient function, the decreased free thyroxine will result in a compensatory increase in thyroxine output by the thyroid. Therefore, patients without a functioning thyroid gland who are on thyroid replacement therapy may need to increase their thyroid dose if estrogens or estrogen-containing oral contraceptives are given."

    Here's the link. Do a page search for estrogen and you'll find the appropriate paragraph. At the top of the page is a link to download the PDF version, which you could print for your GP.

    dailymed.nlm.nih.gov/dailym...

    Hope this helps!

    <b>Updated on Oct 24 2010 12:53PM:</b> P.S. I'd suggest asking for another thyroid blood test asap. This should be automatic when your dose is changed, but it's often overlooked.

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