Birth control pills: what you need to know


By Krista Brooks, MPH, Diana Zuckerman, PhD, Morgan Wharton, and Caitlin Kennedy, PhD. Updated 2014.

Over 10 million women in the U.S. currently use oral contraceptives, or “the pill,” to prevent pregnancy.1, 2 The pill is the most widely used method of birth control.

Many women not only use birth control pills for family planning methods, but also because the pill can alleviate some symptoms associated with their menstruation cycle or “period,” such as acne, anemia due to heavy menstrual bleeding, and premenstrual dysphoric disorder (PMDD).3, 4 PMDD is more than just premenstrual syndrome or PMS.  Women with PMDD suffer from particularly severe depression, tension, or irritability right before they have their period. Birth control pills can also be used to treat the often painful symptoms of endometriosis.

According to a recent report by the Guttmacher Institute, over half of women on oral contraceptives use them, in part, because of acne, anemia, or PMDD.3 As part of the Affordable Care Act (Obamacare), as of August 2012, birth control pills are provided free of charge through all health insurance plans except for plans provided by employers with religious exemptions. 5

With dozens of FDA-approved birth control pills on the market, doctors and patients need to know how they work and how they are tested so that they can decide which pill is best for each woman.  Some provide the same steady dose of hormones throughout the month; some vary the hormones over the course of the month; and some only cause you to have your period a few times a year.  Different pills also use different types of hormones at different dosages.  New types of oral contraceptive pills are introduced every few years, with some sparking controversy over potentially harmful side effects.  Understanding how birth control pills work and how the FDA determines whether they are safe and effective can help demystify the process of choosing the birth control pill that is right for you.

How Birth Control Pills Work

During the menstrual cycle, two hormones (follicle-stimulating hormone or FSH, and estrogen) increase, allowing a mature egg to develop in the ovaries.  Next, ovulation occurs when another hormone (luteinizing hormone or LH) spikes and causes the release of the hormone progesterone.6 Progesterone is important because it allows the lining of the uterus to thicken, creating a good environment for a fertilized egg to attach itself.

Birth control pills contain synthetic forms of estrogen and progesterone.  These synthetic hormones help keep the levels of estrogen and progesterone in your body constant so that eggs do not mature and the lining of the uterus never develops enough for a fertilized egg to implant.  Regulating these hormones in this way also thickens the cervical mucus, making it more difficult for sperm to reach an egg.

If a woman takes contraceptive pills every day, she will never have a period.  However, most packs of birth control pills include a week of pills that do not contain any hormones. These “placebo” or sugar pills reinforce the habit of taking a pill every day so that women will not forget to take the pills with hormones that actually prevent pregnancy.  Women usually expel the lining in their uterus, which results in bleeding similar to a “period” during the four to seven days they take the placebo pills (or if they take no pill at all).

The bleeding you have while taking oral contraceptives is not a real period, because the lining of the uterus does not fully thicken and an egg has not been released.  In other words, birth control pills don’t really “regulate your period,” they just make it seem as though your period is regular.  This is why Seasonale and other birth control pills can safely schedule “periods” only four times a year.  With these pills, you are simply choosing quarterly artificial periods instead of monthly ones.  That’s why birth control pills can interfere with your period even after you stop taking them.  Some women don’t have normal periods for many months after they stop taking birth control pills.  It can take time for the body and natural hormones to adjust, but probably does not affect a woman’s ability to become pregnant.

Emergency Contraception

Emergency contraceptives (the “morning-after pill”) are used after intercourse has already taken place. They prevent pregnancy by delaying the release of an egg from the ovaries and, possibly, by thickening cervical mucus and making “swimming conditions” for sperm unfavorable.7, 8, 9 Studies indicate that emergency contraception does not prevent implantation; it simply keeps the egg and sperm from ever meeting. When women took emergency contraception before they had ovulated, they became pregnant at a much lower rate. When women took emergency contraception after ovulating, they became pregnant at a rate comparable to women who had not taken emergency contraception. If emergency contraception prevented implantation, the women who took it after ovulating would have gotten pregnant at lower rates than women not taking emergency contraception.6, 7 Plan B and ella are the two most common emergency contraceptives. Plan B can be taken up to 72 hours following intercourse and ella may be taken within 120 hours.8 Estimated effectiveness in preventing pregnancy ranges from 52% to 94%.8 Reported side effects include nausea, vomiting, headache, breast tenderness, cramps and fatigue.8, 10 For more information on emergency contraception visit our article on Morning After Pills.

How Has the Pill Changed Over the Years?

Oral contraceptives used to contain high amounts of the hormone estrogen, but now many birth control pills contain a very low dose mix of a synthetic form of estrogen and a synthetic form of progesterone known as progestin.  Manufacturers have lowered the doses and introduced new types of progestin over the years in an effort to decrease side effects such as blood clots.

Birth control pills that contain a mix of estrogen and some form of progestin are known as combined oral contraceptives.  Combined oral contraceptives vary in terms of the types and amounts of estrogen and progestin.  Besides combined oral contraceptives, there are also progestin only pills called the “mini pill,” which is typically prescribed for women who are breastfeeding or cannot take synthetic estrogen.

Generally, the newer types of progestins tend to decrease unwanted side effects such as raising blood sugar, but the newest types (called 3rdand 4th generation progestins) increase the risk of blood clots compared to the older progestins (called 1st and 2nd generation progestins).11


Generations of Progestins

First Generation Second Generation Third Generation Fourth Generation
Norethisterone (NET) Norethindrone (NE)Ethynodiol diacetateLynestrenol (LYN) Levonorgestrel (LNG) Norgestrel (NG) Desogestrel (DSG)Gestodene (GSD)Norgestimate (NGM) Drospirenone (DRSP)

The Risks of Pregnancy and Birth Control

While there are some risks to taking birth control pills, especially if you are over the age of 35, are a smoker, have a history of blood clots or breast cancer, or are currently breastfeeding, combined oral contraceptives are safer than pregnancy.12 While pregnancy is generally safe for healthy young women with good access to prenatal care, there are health risks.  One major study found that the percentage of deaths among women ever using oral contraceptives was 12% lower than those that never did.13, 14 Women on birth control pills have an elevated risk of blood clots, but that risk is lower than the risk of developing blood clots during pregnancy and the six weeks after delivering a child (postpartum).  Also, women who use oral contraceptives have a lower risk of certain cancers, such as ovarian, endometrial, and colorectal.

All birth control pills increase the risk of blood clots compared to not taking birth control pills, but because they are so effective at preventing pregnancy, the FDA has approved birth control pills as safer than being pregnant.  Since birth control pills are more effective at preventing pregnancy than diaphragms or condoms, the FDA does not require them to be as safe.

New research indicates that there are additional risks of birth control pills for women over 40.  A new study found that women over age 40 who had used birth control pills for at least 3 years had an increased risk of developing glaucoma, a degenerative eye disease that may eventually cause blindness.15 Those older women had a 5% risk of developing glaucoma, which is about twice as high as the glaucoma risk for women of the same age and similar traits but who had not taken birth control pills for at least 3 years. The researchers think that this risk may be due to a decrease in estrogen, a hormone that protects eyes, when women take birth control pills. Since all women over 40 are at greater risk of heart disease than younger women, and since birth control pills have cardiac risks as noted above, women over 40 might want to consider other, equally effective types of contraceptives.  Those who stay on birth control pills should consider a yearly eye screening to check for glaucoma as well as annual check-ups to evaluate their heart health.

Does Newer Mean Better, Safer?

Some birth control pills are safer than others.  New birth control pills are introduced on the market all of the time, but newer does not always mean better. The synthetic progestin levonorgestrel, for instance, which has been on the market for decades, seems to be safer than some of the newer synthetic progestins, such as drospirenone.  The latest research on drospirenone, which is in Yaz, Yasmin, and Beyaz (all made by Bayer) and Ocella and Gianvi (the generic forms of Yasmin and Yaz), shows that these pills are significantly more likely to cause blood clots.16 Several studies show them to have twice the risk of other combined hormonal contraceptives.10

To find out more about the risks of drospirenone (also called DRSP), read Are Bayer’s Birth Control Pills Too Risky? You can save yourself some money and reduce the risk of blood clots, which can travel in the body and be fatal, by choosing a birth control pill with a synthetic hormone that has been on the market for a longer time and proven to be safer, such as levonorgestrel.

Do Birth Control Pills Have Other Benefits?

It is important to keep risks such as blood clots in mind if you are considering birth control pills to “regulate your period” or for reasons other than preventing pregnancy.  Is the risk of potentially fatal blood clots worth it to reduce cramping, or might Tylenol or other pain killers be equally effective without the increased risks?  Since birth control pills don’t actually regulate a woman’s period, for example, they should never be used for that purpose.  If the goal is to reduce menstrual bleeding, then birth control pills can accomplish that, but with risks that may not outweigh that benefit.

While all FDA-approved oral contraceptives are proven to prevent pregnancy, some have also been approved for other benefits.17 However, the benefits of birth control pills approved for PMDD—Yaz and Beyaz—have mostly been evaluated by comparing them to placebo-not to other birth control pills.   They may not be any more effective than other, safer, less expensive birth control pills for PMDD.  So, why didn’t the FDA approve these other birth control pills for PMDD?  The answer is simple: money.  Yaz and other relatively new birth control pills are very expensive, and that’s why the company was willing to spend the extra money to apply for FDA approval for PMDD.  Older birth control pills that are widely available in generic forms cost much less, so the companies have no incentive to pay the millions of dollars it would cost to apply for FDA approval specifically for treating PMDD.

The company that makes Yaz and Beyaz, also applied to the FDA for their pills to be approved as helping to reduce acne.  Ortho Tri-Cyclen and Estrostep 21 also are approved by the FDA for birth control and for acne.  Estrostep 21 uses a type of progestin that is believed to have a lower risk of blood clots than the other three.  However, it is unknown if any of those contraceptive pills are better at reducing acne than other birth control pills, whose companies did not apply for FDA approval for acne.  And, birth control pills are less effective at reducing acne than many types of acne medication.

It is important to remember that everyone’s body is different, and pills can have risks or benefits for your friends or relatives that are different from the ones you will experience.  If a particular type of birth control pill is causing problems for you, talk with your health care provider about making a change.  But, even if your pill seems fine, scientific evidence can be used to help us reduce risks.  If you are on a birth control pill that has been shown to have higher risks of blood clots and other complications, why not switch to a safer, less expensive pill?

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