Ethinyl Estradiol (Synthetic Estrogen)

How It Works, Its History, and Its Risks

Ethinyl estradiol (EE) is a synthetic form of estrogen that's mainly used in various hormonal contraceptives, usually in combination with a progestin. It's one of the most commonly used medications.

Packs of birth control pills
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Ethinyl /eth•i•nyl/ [eth´ĭ-nil] Estradiol /es•tra•di•ol/ [es′trədī′ôl] (Estrogen: /ES•troh•jen/ [es′trojən])

Types of Birth Control That Contain Ethinyl Estradiol

Hormonal birth control containing ethinyl estradiol includes:

The Function of Estrogen

Estrogen is a hormone that is usually produced by the female ovaries. It plays an important role in normal female reproductive functioning. Estradiol is a naturally occurring form of estrogen. It helps the female reproductive organs to mature. It also helps your uterine wall to prepare for the implantation of a fertilized egg.

How Estrogen in the Pill Has Changed

Over the years, the amount of synthetic estrogen, ethinyl estradiol, in hormonal birth control has been greatly decreased. The estrogen levels found in today's birth control pills are much safer. When the first birth control pill, Enovid, gained FDA approval in 1960, it did not even contain ethinyl estradiol. Enovid’s formulation consisted of a progestin and 150 micrograms (mcg) of mestranol, a type of estrogen that's converted in the body to become an ethinyl estradiol.

To help put this estrogen level into perspective, 50 mcg of mestranol is equal to about 35 mcg of ethinyl estradiol. So the very first birth control pill brand contained the equivalent of 105 mcg of estrogen. Most combination birth control pills today contain between 20 mcg (low dose pills) to 30/35 mcg of ethinyl estradiol. There are some higher-dose pills that do contain up to 50 mcg, and there is one low dose pill, Lo Loestrin Fe that only has 10 mcg of ethinyl estradiol.

Ethinyl Estradiol in the NuvaRing and Patch

The ethinyl estradiol in the vaginal ring and the birth control patch is similar to birth control pills:

  • The NuvaRing steadily releases 15 mcg of ethinyl estradiol into your body every day. This takes place over a period of 21 days.
  • The Ortho Evra patch delivers 20 mcg of ethinyl estradiol each day for a total of 7 days. But because of the way your body absorbs this hormone, through the skin, your actual exposure to ethinyl estradiol in the patch is more like if you were taking a daily 50 mcg birth control pill.

There's Less Estrogen Today

Overall, today's birth control pill formulations have less than one-third of ethinyl estradiol than earlier versions of the pill. The lower ethinyl estradiol amounts now available in hormonal birth control can offer you both contraceptive and non-contraceptive benefits, with the added bonus of far less unpleasant side effects.

How Ethinyl Estradiol Works

So what can ethinyl estradiol do? Estrogen can help in regulating your period or manage painful periods. Because it helps to stop ovulation, this synthetic estrogen has been found to lower your risk of ovarian cancer as well as endometrial cancer. Plus, because estrogen has the ability to block bone resorption, ethinyl estradiol may also help to increase bone mineral density.

What You Should Also Know About Synthetic Estrogen

Ethinyl estradiol is broken down very quickly in the body. So, to work properly, birth control pills need to be taken at the same time each day. If not, the estrogen may be metabolized too quickly, and the pill’s effectiveness can be lowered.

Certain medications may also cause the liver enzymes to speed up the body's breakdown of estrogen or lower the recirculation of available estrogen within the body, both of which can lead to lower ethinyl estradiol levels and greater chances of pill failure.

Risks and Cautions

There are some women who should not use hormonal birth control that contains ethinyl estradiol. Higher estrogen exposure may be linked to blood clots/venous thromboembolism. This risk increases if you smoke or have specific medical conditions. Some research also suggests that in order to be effective, severely overweight women may need to use birth control with higher levels of ethinyl estradiol. Because of possible side effects and/or certain conditions which may lower the safety of using birth control that contains ethinyl estradiol, it's vital that you fully (and honestly) discuss your lifestyle, habits, and medical history with your healthcare provider. This will help to determine if you're a good fit for a birth control method that contains ethinyl estradiol.

Other Names for Ethinyl Estradiol

Ethinyl estradiol is also known as:

  • Estrogen
  • Ethinyl
  • Ethinylestradiol
  • Synthetic estrogen
  • Estrogen in the pill
  • Mestranol
  • EE
12 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading
  • Runnebaum BC, Rabe T, Kiesel L, eds. Female Contraception: Update and Trends. Germany: Springer-Verlag Berlin and Heidelberg GmbH & Co. K; 2011.

By Dawn Stacey, PhD, LMHC
Dawn Stacey, PhD, LMHC, is a published author, college professor, and mental health consultant with over 15 years of counseling experience.