Even though the birth control pill is greater than 50 years old, it still struggles with many “misconceptions.”
Let’s start with some common questions.
What's in the birth control pill?
“The Pill” contains two hormones: estrogen and progesterone (also called progestins). These are two hormones naturally synthesized in a woman’s body. Estrogen is almost always ethinyl estradiol and it varies by dose. Progestins come in 4 different varieties.
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Estrogen
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Progestin
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50 mcg
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1st Generation: norethindrone, lynestrenol
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35 mcg
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2nd Generation: levonorgestrel, norgestimate
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30 mcg
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3rd Generation: desogestrel, gestodene
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25 mcg
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Drospirenone
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20 mcg
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So, for example, “microgestin” is a pill which contains 20mcg of ethinyl estradiol and 1mg norethindrone. “Yaz” is 20mcg of ethinyl estradiol with 3mg drospirenone.
Typically, pills are taken on a 28 day cycle. 21 days of “active” pills and 7 days of “inactive” pills. Women usually bleed during the inactive pills.
Monophasic: Every “active” pill has the same amounts of estrogen and progestin

Triphasic: Active pills differ in their amount of progestin based on the week

Every week has a different dose of hormones.
How does the pill work?
The pill works in 4 different ways. First, both estrogen and progesterone prevent ovulation (the release of an egg). Second, the progesterone causes the cervical mucous to thicken, and prevents sperm from permeating the cervix. Third, the lining of the endometrium becomes thinner, which prevents implantation. Fourth, the pill decreases tubal motility, which prevents the egg from exiting the fallopian tube.
How do I start the pill?
Instructions for starting the pill are based on one concept: First, make sure you are not pregnant. For this reason, we recommend starting the pill after your period. This is the best way to know you are not pregnant. You can start the pill on the first Sunday after your period. This is useful as it ensures your period will be during the week, rather than the weekend.
Note: if you are pregnant and realize you have been taking the pill, don’t worry. Research has not demonstrated adverse outcomes in this scenario. Stop taking the pill, and find an obstetric provider.
How effective is the pill?
When used perfectly, the pill is 99.7% effective. This means every tablet is taken at the same time everyday. Because the pill is used by humans, perfect use isn’t realistic. Typical use yields an effectiveness of 91.3%. The pill does not protect against sexually transmitted diseases like Gonorrhea, Chlamydia, HIV or Syphilis. Condoms are the best way to protect yourself against sexually transmitted disease and they provide an extra barrier of contraception.
Will the pill make me gain weight?
Although many women report weight gain after starting the pill, large population studies demonstrate that the pill itself does not cause weight gain. The weight gain is often just associated with the time period when the pill was initiated.
Will the pill cause acne?
The early birth control pill had 50mcg of ethynyl estradiol, a much higher dose than today’s pill. With this high dose, some women did experience acne. The low- dose pills used today have a better side effect profile and many women enjoy a clearer skin while on the pill.
So what’s a “low-dose” pill?
Low dose pills are those with 30-35mcg of ethinyl estradiol combined with a progestin. This encompasses most pills prescribed today. “Very-low” dose pills contain 20mcg of estrogen (plus a progestin). And one of the newest pills on the market has just 10mcg of estrogen (plus a progestin). Decreasing the dose of estrogen decreases the risk of adverse events (please see risks below).
Will the pill make me infertile?
No. The pill will prevent pregnancy during the time that you use it correctly. After discontinuing the pill, some women conceive immediately. However, we expect your cycles to return to their previous state after about 2-3 months.
Will my libido (sex drive) disappear after I start the pill?
Some women report a decrease in sex drive after taking the pill. Often this occurs after a few years of use. A decrease in libido is reported in women who are in long term relationships. Women in long term relationships are often taking the pill. For this reason, it is difficult to study this problem. Most women taking the pill do not experience a decrease in sex drive. If you do develop a decrease in libido, there are other contraceptive options.
What are the health benefits of pill use?
When used for 5 years continuously, women have a 2 fold decrease in risk of ovarian cancer. While the pill is used, it protects against endometrial cancer (cancer of the lining of the uterus). The pill does not protect you from abnormal pap smears or cervical cancer. Users of the pill have no increased risk of breast cancer. Periods are generally lighter and shorter in women taking the pill. This is particularly beneficial to women with heavy menstrual bleeding.
What if my period stops while I’m on the pill?
If you don’t bleed in your “inactive” pills, take a pregnancy test. If it is negative, continue using your birth control pills. It is not unusual to skip a period while taking the pill. It is not dangerous to your body. The pill prevents the uterus from building a thick lining. So, at the end of the month, less lining exists to shed.
Can I breastfeed while on the pill?
Early studies and physiologic plausibility led practitioners to avoid prescribing breastfeeding women the pill. Rather, the progesterone only pill (often referred to as "mini-pill") is prescribed instead. The minipill does not affect milk production or fetal growth. However, the progesterone only pill is less effective and needs to be taken at the same time everyday.
What are the risks?
Each person reacts to the pill differently. In general, all women are at risk of having high blood pressure, stroke or venous thromboembolism (a blood clot). These risks are very small, but are dependent on your medical history, and lifestyle. Smoking while on the pill increases your risk of developing a blood clot. Talk to your physician to better understand your individual risk.
Diane A. Christopher MD
Obstetrician and Gynecologist
Boulder, Colorado
303-938-4710
Boulder Medical Center