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What’s the difference between progestin and estrogen in birth control pills?

When considering which oral contraceptive is right for you, two medical terms you might come across are progestin (a synthetic form of progesterone) and estrogen. These refer to two female sex hormones that are used in birth control products. Outside of their use in contraceptives, estrogen and progesterone are naturally produced in the female body and play key roles in regulating certain body functions in women throughout puberty, pregnancy, and menopause.

As two common hormones found in oral contraceptives, understanding the differences between combination pills and progestin-only pills can help you select one that fits your needs and lifestyle. In this article, we will look at the major differences between progestin and  estrogen as it relates to birth control, and why the pill is not “one size fits all.”

What you need to know about progestin

Progestin is a synthetic form of progesterone, which is a female hormone found in a woman’s body. As a naturally occurring hormone, progesterone is released from the ovaries to prepare the body for pregnancy. Progesterone also plays an important role during pregnancy. It contributes to maternal breast tissue growth while also preventing lactation, and prepares the body for labor by strengthening the wall muscles around the pelvic area.

Some common uses for progestin in products outside of contraception include treating abnormal uterine bleeding, severe premenstrual syndrome (PMS), and postmenopausal hormone replacement therapy.

Do progestin products have any adverse side effects? When taking oral contraceptives that contain progestin, some women may experience side effects including ovarian cysts, breast tenderness, headaches, fatigue, nausea, and hair thinning.

Other studies analyzing other side effects, such as the impact on sex drive and development of mood disturbances, are limited in terms of evidence and may offer conflicting views.

If you’re experiencing any adverse side effects when taking oral contraceptives, make sure to talk to your doctor.

Woman speaking to a doctor

What you need to know about estrogen

Like progesterone, estrogen is a sex hormone naturally produced in the body and is responsible for developing female sexual characteristics. For example, during puberty, estrogen contributes to the development of mammary ducts. During pregnancy, it supports functions that secrete breast milk.

Estrogen is commonly found in birth control products, such as oral contraceptives and vaginal rings. It is also found in products that treat symptoms during menopause, such as hot flashes, vaginal dryness, and itching.

Some side effects of taking estrogen products include nausea, cramps, headaches, weight gain, and abnormal uterine bleeding.

If you’re experiencing any adverse side effects when taking oral contraceptives, make sure to talk to your doctor.

Combination birth control pills or progestin-only pills?

Combination Oral Contraceptives (COCs)

Combination birth control pills contain both estrogen and progestin. When used in birth control pills, progestin and estrogen thicken the mucus inside the cervix, making it harder for sperm to travel to the egg. They also work to thin the lining of the uterine wall so that if an egg is fertilized, it is more difficult to implant.

COCs are most effective when the pills are taken correctly according to the instructions. Most products on the market use a one-phase dosing cycle, or monophasic. In other words, tablets of one strength are taken for 21 days. A monophasic dosing cycle with 28 days will include seven inactive or placebo pills that are another color.

Other dosing schedules include biphasic (two-phase), triphasic (three-phase), and even quadriphasic (four-phase). The differences between these phases are the number of different colored pills formulated with different strengths. The benefit of a monophasic dosing cycle is that it’s much more straightforward and easier for patients to remember—they don’t have to remember what color pill corresponds to what formulation strength. Learn more about dosing schedules in this Mayo Clinic article.

Combined birth control pills typically have a tight 3-hour dosage window. They contain varying levels of estrogen and also in different forms (chewables, soft gels, tablets).

Chewables or soft gels have similar side effects as other traditional combined pills, including headaches, breakthrough bleeding, nausea, and weight gain. However, similar to other COC products, side effects may vary from person to person.

A benefit of chewable birth control is that it may be easier to swallow, especially for women who are experiencing nausea. While not chewable, soft gel capsules are more flexible and easier to swallow than traditional pills.

It is important to note that all combined oral contraceptives contain a boxed warning about the increased risk of heart and blood vessel problems as well as death from blood clots, heart attack, or stroke in females that smoke and are over 35, which increases with age and the number of cigarettes smoked and is therefore not recommended in this group.

Progestin Only Pills (POPs)

Progestin-only pills (POPs) only contain progestin (no estrogen) and typically have a lower dose of progestin compared to a combination pill with both progestin and estrogen. Progestin-only birth control pills also prevent pregnancy by thickening the mucus of the cervix and thinning the lining of the uterine wall.

For women who are breastfeeding and want to take oral contraception, doctors may recommend a progestin-only pill since estrogen may interfere with the production of breastmilk.

POPs are also a more suitable option for women who smoke and are over the age of 35 because they do not contain estrogen. Patients with a history of blood clots or high blood pressure are better off taking a POP due to the increased cardiovascular risk seen with combined oral contraceptives.

Doctors may not recommend POPs for women who have had breast cancer, have liver disease, serious cardiovascular risk, have had cardiovascular surgery or other issues, or take other drugs that may interfere with the effectiveness of the pill.

For a very long time, progestin-only pills only offered a tight 3-hour dosage window during which a woman must take her pill for maximum effectiveness in pregnancy prevention. However, that changed when Slynd® entered the market. Slynd® is the first and only POP with a 24-hour missed pill window, comparable to COCs.

Package of Slynd® Birth Control Pills

When deciding between a combination oral contractive or a progestin-only pill, consult your healthcare provider to learn more about which option best suits you.

Click here to learn more about how Slynd® may fit your needs.

Do not take Slynd® if you:

  • have kidney disease or kidney failure
  • have reduced adrenal gland function (adrenal insufficiency)
  • have or have had cervical cancer or any cancer that is sensitive to female hormones
  • have liver disease, including liver tumors
  • have unexplained vaginal bleeding

If any of these conditions happen while you are taking Slynd®, stop taking Slynd® right away and talk to your healthcare provider. Use non-hormonal contraception when you stop taking Slynd®.

Click here to read more Important Risk Information and Full Prescribing Information.

Slynd® is a trademark of Chemo Research, S.L.

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