What is Ethinylestradiol and how does it Work?

What is Ethinylestradiol?

Ethinylestradiol is a synthetic form of oestrogen (like the hormone oestrogen naturally found in your body but made in a lab). Ethinylestradiol is used in most brands of combined hormonal contraception, alongside a synthetic progestogen, including in the combined oral contraceptive pill, the contraceptive patch and the vaginal ring. It may also be prescribed on its own for the short term treatment of the symptoms of oestrogen deficiency. 

How does it work?

Ethinylestradiol is metabolised by the liver into estradiol (aka oestrogen), and works with the progestogen in the combined pill to stop ovulation (the release of an egg from the ovaries), stopping fertilisation of an egg by sperm and preventing pregnancy. Estradiol also regulates the lining of the womb helping to prevent breakthrough bleeding on the pill.

What is it used in?

Pretty much every combined contraceptive! Combined pill brands containing ethinylestradiol include:

Helpfully the patch and the vaginal ring only have a few brands available in the UK currently – the Evra patch, the NuvaRing and SyreniRing. These all also contain ethinylestradiol. The way the hormones are delivered in the patch or ring may have benefits for individuals over the pills.

Ethinylestradiol side effects

Possible side effects of combined hormonal contraceptive methods caused by oestrogen include: 

• Bloating
• Breast tenderness or swelling
• Reduced sex drive
• Headaches
• Mood swings
• Nausea or vomiting
• Water retention

What are the risks?

Typically, increased risk of blood clots with the combined hormonal methods of contraception has been associated with the oestrogen component. Oestrogen receptors in the liver are involved in the production of blood clotting factors. Ethinylestradiol is much more potent than natural estradiol, and it remains in the body far longer, so it hyperactivates the liver pathway, creating conditions that promote blood clotting.

To decrease the risks of blood clots and other side effects, the dose of synthetic oestrogen in combined contraceptive pills has been gradually dropping over time. Blood clot risk varies slightly between different brands of combined pill, depending on the type of progestogen. However for women who already are at an increased risk of blood clots there are other safer methods of contraception available which do not contain oestrogen