How Estrogen Drugs Affect Your Thyroid

Woman holding birth control pill pack
Anne Rippy/Getty Images

The majority of people who have hypothyroidism—an underactive thyroid—in the United States are women. The majority of these women are of childbearing age or are perimenopausal/menopausal. This means that while being treated for their hypothyroidism, some of them are also taking prescription medications such as contraceptive pills or undergoing hormone replacement therapy.

According to research from the Guttmacher Institute, an estimated 10 million+ women between the ages of 15 and 44 use the contraceptive pill for birth control.

An estimated 57 to 75 million prescriptions for hormone replacement therapies, most of them including some form of estrogen, are written in the United States. Some experts estimate that as many as 5 percent of all peri- and post-menopausal women are taking both hormone replacement therapy and thyroid hormone replacement medication.

It’s important for any woman who is taking thyroid hormone replacement drugs to treat hypothyroidism—such as levothyroxine or natural desiccated thyroid—to be aware of the effects that drugs containing estrogen can have on the thyroid and treatment of hypothyroidism. Similarly, you need to be aware if you are prescribed hormone replacement medication for hypothyroidism after being on a contraceptive pill that contains estrogen, or you are already taking a hormone replacement therapy that includes any form of estrogen.

The Effects of Estrogen on the Thyroid

Increases in estrogen can be a result of pregnancy, certain genetic predispositions, and use of medications such as contraceptive pills or hormone replacement therapy. Estrogens that are taken as medications can be in the form of synthetic estrogens such as ethinylestradiol, or bioidentical forms of estrogen such as estradiol, estriol, or estrone. Estradiol is also known as 17 beta-estradiol.

Whether the increased estrogen is being produced by your body or taken as an oral medication, that estrogen has the ability to raise your levels of thyroxine-binding globulin, known as TBG. TBG is a special protein known as a “globulin.” The role of TGB is to attach to the two key thyroid hormones—thyroxine (T4) and triiodothyronine (T3)—circulating in your bloodstream, and to help transport those hormones to your cells.

When TBG is elevated, the TBG binds up more of your thyroid hormone, and as a result, it lowers the amount of free thyroid hormones available in your bloodstream. This, in turn, can lead to an increase in your TSH level, which can then stimulate the production of more thyroid hormone.

According to research, after just six weeks of estrogen therapy, the TBG rises in a significant number of hypothyroid women. The increase in TBG typically peaks at about 12 weeks after starting therapy. Similarly, Free T4 levels drop—and in some cases, TSH rises—in a parallel way during that timeframe. These changes are not typically seen in women who are not hypothyroid.

Next Steps for Thyroid Patients

1. Recheck Thyroid Function After Starting and Stopping the Pill or Hormone Replacement

Healthy women typically experience no significant changes in thyroid function while on contraceptives or hormone replacement therapy with estrogen. Research has shown, however, that about 40 percent of women who are taking thyroid hormone replacement medication who add a medication that contains estrogen have decreases in blood levels of T4. This means that hypothyroidism symptoms such as fatigue and weight gain can return unless the dosage of thyroid medication is increased. This is also a risk for women who have survived thyroid cancer and need to keep thyroid hormones suppressed to help prevent thyroid cancer recurrence.

Because almost half of hypothyroid women will be impacted by estrogen, it’s important to get your thyroid rechecked within three months if you are on thyroid hormone replacement medication and start or stop an oral contraceptive or an oral estrogen medication. You may need an increase or decrease in your dosage of thyroid hormone replacement medication.

2. Don’t Stop Taking Your Contraceptive Pills or Hormone Replacement Without Checking Thyroid Function

According to researcher Dr. Robert Utiger, some hypothyroid women taking estrogen or birth control may experience symptoms, and decide to stop taking their hormone replacement, birth control, or hormone replacement. Instead, according to Dr. Utiger, checking thyroid hormone levels and increasing the thyroid hormone medication dosage could potentially resolve the issue for those women.

3. Consider the Mini-Pill for Contraception

The majority of contraceptive pill users take a “combination” pill that combines synthetic estrogen and progesterone. Some of the popular brands of these monthly combination pills include Lo/Ovral, Loestrin, Lybrel, Mircette, Norinyl, Ortho-Novum, Ortho Tri-Cyclen, Seasonique, Seasonale, Yasmin, and Yaz. These pills can all affect TBG levels and thyroid function.

Contraceptive birth control pills that do not include estrogen do not affect TBG levels, and as a result, are not likely to alter thyroid function. These estrogen-free contraceptive pills are sometimes called the "mini-pill." Some of the popular brand names of these estrogen-free pills include Camila, Errin, Micronor, Nor-Q.D., Norethindrone, and Ovrette. The estrogen-free contraceptive pills are less frequently used when compared to combination pills, and there are some questions as to whether they are considered as effective.

Combination pills are more effective for pregnancy prevention than the “mini pill.” When taken correctly, the combination pill is rated between 91% and 99.9% effective. (When taken correctly, the mini-pill is rated from 87% up to 99.7% effective.)

If you are on thyroid hormone replacement medication and want to ensure that your thyroid treatment will not be affected by contraceptive pills with estrogen, however, you should discuss the “mini-pill” with your healthcare practitioner.

4. Consider the Contraceptive Patch

There is a birth control patch, applied to the skin, that has the same combination of hormones, delivered transdermally (through the skin), as oral pills. Some popular brands of the patch include Ortho Evra and Xulane.

These birth control patches do not affect TBG levels, and as a result, are not likely to alter thyroid function.

If you are on thyroid hormone replacement medication and want to ensure that your thyroid treatment will not be affected by contraceptive pills with estrogen, you should discuss the option of using the birth control patch with your healthcare practitioner.

5. Consider Transdermal Forms of Hormone Replacement Therapy

Research has shown that only oral forms of estrogen have an effect on TBG levels. The popular brand-names of oral (pill) forms of estrogen-only or combination hormone replacement therapy include Activella, Angeliq, Cenestin, Enjuvia, Estrace, Femhrt, Femtrace, Menest, Prefest, Premarin, and Prempro.

If you are considering hormone replacement therapy that includes estrogen, you should consider transdermal forms of estrogen-only or combination hormone replacement therapy, such as patches, gels, or vaginal tablets and inserts. The popular brands include the Alora patch, the Climara patch, Combipatch patch, Divigel gel, Extraderm patch, Estring vaginal insert, EstroGel gel, Evamist spray, Minivell patch, Vagifem vaginal tablet, and the Vivelle patch.

View Article Sources
  • Agren, U et. Al. “Effects of a monophasic combined oral contraceptive containing nomegestrol acetate and 17β-oestradiol in comparison to one containing levonorgestrel and ethinylestradiol on markers of endocrine function.” Eur J Contracept Reprod Health Care. 2011 Dec;16(6):458-67. doi: 10.3109/13625187.2011.614363. Epub 2011 Sep 26.
  • Guttmacher Institute. "Contraceptive Use in the United States: 2016 Fact Sheet."
  • Pinkerton, J, Santoro, N. "Compounded bioidentical hormone therapy." Menopause, 2015; 1 DOI: 10.1097/GME.0000000000000420
  • Raps, M et. Al. “Use of hormonal contraceptives lead to elevated TBG levels, slightly elevated TSH levels.” Thromb Res. 2014 Apr;133(4):640-4. doi: 10.1016/j.thromres.2013.12.041. Epub 2014 Jan 7.
  • Santin, A et al.  “Role of Estrogen in Thyroid Function and Growth Regulation.” J Thyroid Res. 2011; 2011: 875125. Published online 2011 May 4. doi:  10.4061/2011/875125