Birth Control Pills

Birth control pills (also called oral contraceptives or “the pill”) are used by millions of women in the United States to prevent pregnancy. The pill is safe and effective for most women.


To understand how birth control pills work, you should know what happens during reproduction. A woman has two ovaries, one on each side of the uterus. Each month, one of the ovaries releases an egg into a fallopian tube. This is called ovulation. It typically occurs about 12-14 days before the start of the menstrual period.

A woman can get pregnant if she has sex around the time of ovulation. During sex, the man ejaculates sperm into the vagina. The sperm travel up through the cervix and into the fallopian tubes.

When a sperm meets an egg in the fallopian tube, fertilization-union of egg and sperm-can occur. The fertilized egg then moves down the fallopian tube to the uterus. It then attaches to the lining of the uterus and grows into a fetus.

Birth Control Pills

Birth control pills are made of hormones that prevent ovulation. The hormones in the pill also cause changes in the cervical mucus and the lining of the uterus. The cervical mucus thickens, which blocks the sperm from entering the cervix. The lining of the uterus thins, making it less likely that a fertilized egg can attach to it. Together, these events make it very unlikely that someone taking the pill will become pregnant.

The pill is a very effective form of birth control. When women use the pill correctly, fewer than 1 in 100 will get pregnant over 1 year. But, about 8 in 100 typical users (8%) will become pregnant. This is because one or more pills may be missed or are not absorbed (due to vomiting for instance). If this occurs, a backup method of birth control, such as a condom or spermicides, should be used. If pills are missed and a backup method is not used, emergency contraception can be used to prevent pregnancy.

The birth control pill is easy to use and convenient. But it does not protect against sexually transmitted diseases (STDs). If you are at risk for STDs, you should use condoms for protection.

Although rare, some types of pills can cause severe illness in some women. The most serious problems are blood clots in the legs or lungs, heart attack, or stroke. Other rare problems that may occur include high blood pressure and problems with the liver and gallbladder. So, before your doctor or nurse will prescribe birth control pills for you, he or she will ask some questions about your health and your family history. He or she also may do a physical exam, which may include a pelvic exam and a breast exam.

Combination Pills

Combination birth control pills contain the hormones estrogen and progestin (a synthetic form of the hormone progesterone).

There are many different brands with different does of hormones. This gives a woman a choice in finding a pill that is right for her.

How to Take Them

Based on convenience and advice of their doctors, different women may start taking their pills at different times. Discuss your options with your doctor:

  • You can start taking the pill on the first day of your period. You will not need a backup method of birth control.
  • You can start taking the pill on the Sunday after your period starts. With this method you will have to use a backup birth control method for the next 7 days of the first cycle.
  • You also can start taking the pill on the day it is prescribed, no matter where you are in your cycle. In this case, you will need to make sure that you are not pregnant and you will need to use a backup method of birth control for the first month.

No matter which day you choose to start taking the pill, you will start each new pack of pills on the same day of the week as you started the first pack. It is a good idea to have an extra pack of pills and a backup method on hand in case you miss some pills or lose your pack.

Pills work only if you take them correctly. Do not skip pills for any reason-even if you bleed between periods or feel sick. Call your doctor or nurse if you are concerned. Even if you do not have sex very often, you should keep taking the pill.

Your pills may not work well if your body does not absorb them. This may happen if you are taking certain medications, such as antibiotics, or if you vomit. If you can’t keep your pill down, you should use a backup method for the rest of your cycle.

Pills come in packs of 21, 28, or 91 pills:

21 pills

If your pack has 21 pills, take one pill at the same time each day for 21 days. Wait 7 days before starting a new pack. During the week you are not taking the pill, you will have your period. You will start your new pack of pills on the same day of the week as you started the first pack.

28 pills

If your pack has 28 pills, take one pill at the same time each day for 28 days. The first 21 pills contain hormones. The last seven do not. During the week you are taking the last seven pills, you will have your period. When you finish all the pills in the pack, start a new pack the next day.

91 Pills (also called continuous dosing or extended use)

You will take a pill every day at the same time each day for 91 days. The first 84 pills contain hormones. The last seven do not. During the week you are taking the last seven pills, you will have your period. This means you will have only four periods in a year. Some women eventually may have no periods.

Each new pack of pills comes with facts about the pill. Be sure to read this information and ask your doctor about anything that is not clear to you.


The combination birth control pill has benefits in addition to preventing pregnancy. Using this type of birth control pill may reduce the risk of certain health problems:

  • Cancer of the uterus and ovary
  • Ovarian cysts
  • Pelvic infection
  • Bone loss
  • Benign breast disease
  • Symptoms of polycystic ovary syndrome
  • Anemia (iron poor blood)
  • Ectopic pregnancy
  • Acne

The pill also helps to keep you periods regular, lighter, and shorter and reduces menstrual cramps. Some women use continuous dosing birth control because they want to have fewer periods. For others, this method can help relieve symptoms of problems that are affected by having periods, such as endometriosis or fibroids. Taking hormones continuously also may help with migraine headaches and depression.

Some women are afraid to take the pill because they have a family history of breast cancer. Most experts agree that women with a family history of breast cancer and no other risks factors do not increase their risk of breast cancer by taking the pill.

Progestin-Only Pills

Another type of birth control pill, called the progestin-only pill or the minipill, contains only progestin. The progestin-only pill is a better choice for women who have certain health problems-such as blood clots-and cannot take pills with estrogen. This method also may be the best choice for women who had side effects with the combination birth control pill or who are breastfeeding.

How to Take Them

The minipill comes in packs of 28 pills. All the pills in the pack contain hormones. It is important not to miss a pill. It is very important to take a progestin-only pill at the same time each day. So, it may not be a good choice for people who have trouble keeping to a schedule. You should use a backup method of contraception for 48 hours if vomiting occurs after taking a pill or if you are 3 or more hours late in taking a pill.


Progestin-only pills do not offer the same benefits that combination birth control pills offer. Most people who choose progestin-only pill do so because there are reasons they should not take estrogen. Progestin-only pills offer some protection against:

  • Cancer of the uterus and ovaries
  • Benign breast disease
  • Pelvic inflammatory disease

Side Effects

Depending on the type of pill, some women may have one or more of the following side effects when taking the pill:

  • Headache
  • Nausea
  • Dizziness
  • Breakthrough bleeding
  • Missed periods
  • Tender breasts
  • Depression
  • Anxiety

For nausea, many women find that taking the pill with a meal or before bed helps. For headaches, taking over-the-counter products for pain relief often helps.

Women who take the progestin-only pill may have more bleeding or spotting days than women who take birth control pills that contain estrogen.

Missing a period also is common. If you miss one period and have taken the pill as prescribed, you should keep taking the pill. If you have forgotten some pills and miss one period, call your doctor. Don’t stop taking the pill. It is not likely that you are pregnant. Using birth control pills during pregnancy does not increase the risk of birth defects.

Most side effects are minor and often go away after a few months of use. There will likely be fewer side effects if the pill is taken at the same time every day.


The pill is a good choice for women who may want to get pregnant later. It is a safe and effective way to prevent pregnancy. It is easy to use, convenient, and reversible. The pill may protect against some cancers. Some benefits of pills last months or years after you stop taking it. For almost all women, the benefits of pill use outweigh the risks.