Levothyroxine and Estrogen Interaction

Content provided by the Faculty of the Harvard Medical School

Levothyroxine and Estrogen Interaction

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Question:

Is there any interaction from taking levothyroxine and birth control pills together?

Answer:

Most birth control pills contain a combination of two female hormones, estrogen and a progestin. Assuming that your pill contains estrogen, it will interact with the levothyroxine (a synthetic type of thyroid hormone).

The explanation for this interation gets a little complicated. But the bottom line is you don't need to stop the birth control pills. You may need to take a slightly higher dose of levothyroxine while you are on the estrogen-containing pill.

Your doctor can order a blood test called TSH (thyroid stimulating hormone) to see if your thyroid dose needs to be a little higher.

The interaction between estrogen and levothyroxine also applies to women who take estrogen for relief of menopausal symptoms.

Howard LeWine, M.D., is chief editor of Internet Publishing at Harvard Health Publications. He is recognized as an outstanding clinician and teacher and is a recipient of the Internal Medicine Teacher of the Year award at Brigham and Women's Hospital. Dr. LeWine continues to practice Internal Medicine; most recently he became a hospitalist after practicing primary care for over 20 years.

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Last updated:	July 20, 2009

Medical content reviewed by the Faculty of the Harvard Medical School. Harvard Health Publications, Copyright © 2007 by President and Fellows of Harvard College. All rights reserved. Used with permission of StayWell.

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