The birth control pill, also known as oral contraceptives or just “the pill,” is a medication taken daily to prevent pregnancy. Some women take the pill for reasons other than preventing pregnancy.

Combined pills contain two hormones, estrogen and progestin. Hormones are chemicals that control how different parts of your body work. These pills are taken every day and prevent pregnancy by keeping the ovaries from releasing eggs. The pills also cause cervical mucus to thicken and the lining of the uterus to thin. This keeps sperm from meeting with and fertilizing an egg.

Progestin-only pills (or “mini-pills”) contain only one hormone, progestin which causes cervical mucus to thicken and the lining of the uterus to thin. This keeps sperm from reaching the egg. Less often, mini-pills prevent pregnancy by keeping the ovaries from releasing eggs.

Combined pills are typically packaged as 21 “active” pills that contain hormones. One pill is taken daily for three weeks, followed by one week off. Others are packaged as 28 pills that include 21 “active” pills taken daily, followed by one week of “inactive” reminder pills that don’t contain hormones.

Some newer formulations have increased the number of active pills to 24 and reduced the inactive pills to 4. With all combined pill formulations, protection against pregnancy continues during the week where no active pills are taken.

Some women use combined pills to limit the number of periods they have, or even to prevent them altogether:

• Extended Cycle use involves taking 12 weeks of active pills followed by one week of inactive pills. Women on anextended cycle have three or four periods a year.

• Continuous Use of pills is where a woman takes an active pill every day so she won’t have any periods at all.

Mini-pills come only in packages of 28-day “active” pills. It is important to take mini-pills every day, and to take them at the same time each day. If you’re late taking a mini-pill by more than three hours, you’ll need to use another type of birth control (such as a condom or sponge) to prevent pregnancy, but continue also to take the mini-pill.

All types of birth control pills should be taken exactly as directed by your health care provider, even on days when you don’t have sex.

Of 100 women who use this method each year, about nine women may get pregnant on the combined pills and five will get pregnant on the mini-pills. The risk of pregnancy is much less for women who take the pill correctly—every day at about the same time. Certain medications such as Rifampin (taken to treat tuberculosis) and supplements (such as St. John’s Wort) may make the pill less effective. Talk with your health care provider if you have any questions about birth control pills.

• The pill is easy to use.

• Birth control pills are safe and work well in preventing pregnancy. Using the pill means you don’t have to think about birth control when you want to have sex.

• Combination pills may offer other benefits such as fewer menstrual cramps, decreased menstrual blood loss,less acne, and stronger bones. They also reduce the risk of some cancers that affect reproductive organs.

• Fertility returns to normal when women discontinue use.

• The health benefits from Oral Contraceptives are manifold, including protection from endometrial cancer. A study published in The Lancet Oncology estimates that the use of OCPs has prevented about 400,000 cases of endometrial cancer in high-income countries over the last 50 years. Of these, about 200,000 have been prevented in the last decade itself. Further, the use of OCPs even for a few years (typically in the 20s or 30s) can protect women into their 50s and older, when they are more prone to cancers. The researchers estimate that every five yeas of use reduces the risk of endometrial cancer by about a quarter. This reduction does not vary substantially by women's reproductive history, adiposity, alcohol use, tobacco use or ethnicity.

• The pill does not protect against sexually transmitted infections (STIs), including HIV.

• You must take your pills every day.

• Certain medications such as Rifampin (taken to treat tuberculosis) and supplements (such as St. John’s Wort) may make the pill less effective.

• Combined pills may cause nausea, changes in your menstrual cycle, breast tenderness or headaches. Discuss your medical history with your health care provider before using any birth control pill, and let them know if you develop any side effects.

• It is uncommon, but some women develop high blood pressure.

• Rarely, use of the combined pill increases the risk of blood clots, heart attack, and stroke. The risk of blood clots increases for very overweight women who use the combined pill.

No. There is no evidence that taking a "rest" is helpful. In fact, taking a "rest" from COCs can lead to unintended pregnancy. COCs can safely be used for many years without having to stop taking them periodically.

No. A woman is protected only as long as she takes her pills regularly.

Women who stop using COCs can become pregnant as quickly as women who stop non-hormonal methods. COCs do not delay the return of a woman’s fertility after she stops taking them. The bleeding pattern a woman had before she used COCs generally returns after she stops taking them. Some women may have to wait a few months before their usual bleeding pattern returns.

No. Research on COCs finds that they do not disrupt an existing pregnancy. They should not be used to try to cause an abortion. They will not do so.

No. Good evidence shows that COCs will not cause birth defects and will not otherwise harm the fetus if a woman becomes pregnant while taking COCs or accidentally starts to take them when she is already pregnant.

No. Most women do not gain or lose weight due to COCs. Weight changes naturally as life circumstances change and as people age. Because these changes in weight are so common, many women think that COCs cause these gains or losses in weight. Studies find, however, that, on average, COCs do not affect weight. A few women experience sudden changes in weight when using COCs. These changes reverse after they stop taking combined oral contraceptives. It is not known why these women respond to COCs in this way.

Generally, no. Some women using COCs report these complaints. The great majority of COC users do not report any such changes, however, and some report that both mood and sex drive improve. It is difficult to tell whether such changes are due to the COCs or to other reasons. Providers can help a client with these problems. There is no evidence that COCs affect women’s sexual behavior.

The provider can point out that both COC users and women who do not use COCs can have breast cancer. In scientific studies breast cancer was slightly more common among women using COCs and those who had used COCs in the past 10 years than among other women. Scientists do not know whether or not COCs actually caused the slight increase in breast cancers. It is possible that the cancers were already there before COC use but were found sooner in COC users.

No. A woman may experience some vaginal bleeding (a “withdrawal bleed”) as a result of taking several COCs or one full cycle of COCs, but studies suggest that this practice does not accurately identify who is or is not pregnant. Thus, giving a woman COCs to see if she has bleeding later is not recommended as a way to tell if she is pregnant. COCs should not be given to women as a pregnancy test of sorts because they do not produce accurate results.

No. A pelvic examination to check for pregnancy is not necessary. Instead, asking the right questions usually can help to make reasonably certain that a woman is not pregnant. No other condition that could be detected by a pelvic examination rules out COC use.

Yes. COCs are safe for women with varicose veins. Varicose veins are enlarged blood vessels close to the surface of the skin. They are not dangerous. They are not blood clots, nor are these veins the deep veins in the legs where a blood clot can be dangerous (deep vein thrombosis). A woman who has or has had deep vein thrombosis should not use COCs.

Yes. There is no minimum or maximum age for COC use. COCs can be an appropriate method for most women from onset of monthly bleeding (menarche) to menopause. 

COCs can be an appropriate method for adolescents. Adolescents may need extra support and encouragement to use COCs consistently and effectively.

Women younger than age 35 who smoke can use COCs. Women age 35 and older who smoke should choose a method without estrogen or, if they smoke fewer than 15 cigarettes a day, monthly injectables. Older women who smoke can take the progestin-only pill if they prefer pills. All women who smoke should be urged to stop smoking.

A woman who answers “No” to all 6 questions on the Pregnancy Checklist can still start taking COCs. Ask her to come back for a pregnancy test if her next monthly bleeding is late.

Yes. As soon as possible, but no more than 5 days after unprotected sex, a woman can take COCs as Emergency Contraceptive Pills. Progestin-only pills, however, are more effective and cause fewer side effects such as nausea and stomach upset.

Monophasic pills provide the same amount of estrogen and progestin in every hormonal pill. Biphasic and triphasic pills change the amount of estrogen and progestin at different points of the pill-taking cycle. For biphasic pills, the first 10 pills have one dosage, and then the next 11 pills have another level of estrogen and progestin. For triphasic pills, the first 7 or so pills have one dosage, the next 7 pills have another dosage, and the last 7 hormonal pills have yet another dosage. All prevent pregnancy in the same way. Differences in side effects, effectiveness, and continuation appear to be slight.

A woman can take her COCs at different times of day, and they will still be effective. However, taking them at the same time each day can be helpful for 2 reasons. Some side effects may be reduced by taking the pill at the same time each day. Also, taking a pill at the same time each day can help women remember to take their pills more consistently. Linking pill taking with a daily activity also helps women remember to take their pills.

It is desirable for all women to have blood pressure measurements taken routinely before starting a hormonal method of contraception. However, in some settings blood pressure measurements are unavailable. In many of these settings, pregnancy-related morbidity and mortality risks are high, and these methods are among the few methods that are widely available. In such settings women should not be denied use of these methods simply because their blood pressure cannot be measured.

Women with high blood pressure or very high blood pressure should not use combined hormonal methods—COCs, monthly injectables, patch, or combined ring. Where blood pressure cannot be measured, women with a history of high blood pressure should not use these methods. Women with very high blood pressure should not use progestin-only injectables. Women can use progestin-only pills (POPs), implants, and LNG-IUDs even if they have high or very high blood pressure readings or a history of high or very high blood pressure.

High blood pressure is defined as systolic pressure 140 mm Hg or higher or diastolic pressure 90 mm Hg or higher. Very high blood pressure is defined as systolic pressure 160 mm Hg or higher or diastolic pressure 100 mm Hg or higher.