Combination birth control pills, also known as the pill, are oral contraceptives that contain estrogen and a progestin.

Combination birth control pills suppress ovulation — keeping your ovaries from releasing an egg. Combination birth control pills also cause changes in the cervical mucus and the lining of the uterus (endometrium) to keep sperm from joining the egg.

Different types of combination birth control pills contain different doses of estrogen and progestin. Some combination birth control pills, called continuous or extended-cycle pills, allow you to reduce the number of periods you have each year. If you'd like to use combination birth control pills, your health care provider can help you decide which type is right for you.

Combination birth control pills are a reliable form of contraception that is also easily reversed. Fertility may return to normal two weeks after stopping combination birth control pills. Combination birth control pills have noncontraceptive benefits as well, such as:

  • Decreased risk of ovarian and endometrial cancers, ectopic pregnancy, ovarian cysts, uterine fibroids, benign breast disease
  • Improvement in acne
  • Less severe menstrual cramps (dysmenorrhea)
  • Possible decreased risk of postmenopausal hip fracture
  • Reduction in androgen production caused by polycystic ovary syndrome
  • Reduction in menorrhagia and related iron deficiency anemia
  • Relief from premenstrual syndrome (PMS)
  • Shorter, lighter and more predictable periods or, for some types of combination pills, fewer periods each year

Combination birth control pills come in different mixtures of active and inactive pills, including:

  • Conventional pack. The most common type of combination birth control pills contains 21 active pills and seven inactive pills. Formulations containing 24 active pills and four inactive pills, known as a shortened pill-free interval, also are available. Bleeding occurs every month during the week when you take the last four to seven inactive pills.
  • Continuous dosing or extended cycle. These combination birth control pills typically contain 84 active pills and seven inactive pills. Bleeding generally occurs only four times a year during the week when you take the last four to seven inactive pills. Formulations containing only 28 active pills — eliminating bleeding — also are available.

Continuous dosing or extended cycle pills may provide additional benefits of suppressing menstruation, such as:

  • Prevention and treatment of excessive bleeding related to uterine fibroids
  • Prevention of menstrual migraine
  • Reduction in the menstruation-associated worsening of certain conditions, including seizures and asthma
  • Relief from pain related to endometriosis

Combination birth control pills aren't appropriate for everyone, however. Your health care provider may suggest another form of birth control instead of combination birth control pills if you:

  • Are breast-feeding
  • Are older than age 35 and smoke
  • Have poorly controlled high blood pressure
  • Have a history of or current deep vein thrombosis or pulmonary embolism
  • Have a history of stroke or heart disease
  • Have a history of breast cancer
  • Have migraines with aura
  • Have diabetes-related complications, such as nephropathy, retinopathy or neuropathy
  • Have liver disease
  • Have unexplained uterine bleeding
  • Will be immobilized for a prolonged period due to major surgery

An estimated 8 out of 100 women taking combination birth control pills will get pregnant in the first year of use. Although taking combination birth control pills during early pregnancy doesn't increase the risk of birth defects, it's best to stop taking birth control pills as soon as you suspect you're pregnant.

Combination birth control pills won't protect you from sexually transmitted infections.

Combination birth control pills can cause side effects such as:

  • Breakthrough bleeding or spotting (more common with continuous or extended-cycle pills)
  • Breast tenderness
  • Decreased libido
  • Elevated blood pressure
  • Headaches
  • Mood changes
  • Nausea

Some side effects — including nausea, headaches, breast tenderness and breakthrough bleeding — may last only a few months or be less noticeable if you take the pill at the same time every day.

Combination birth control pills increase the risk of certain conditions. Some of these complications can be serious. They include the following:

  • Blood clots in the legs (recent studies suggest that the type of progestin used in the pill may affect the risk of blood clots, with pills containing drosperinone showing a higher risk)
  • Gallbladder disease
  • Heart attacks and stroke (smoking greatly increases the risk of these complications)
  • Liver tumors

Consult your health care provider as soon as possible if you're taking combination birth control pills and have:

  • Abdominal pain
  • Breast lump
  • Chest pain
  • Depression
  • Difficulty speaking
  • Eye problems, such as blurred or double vision or loss of vision
  • Fainting
  • Jaundice (yellowish discoloration of the skin)
  • New or worsening headaches
  • Seizure
  • Severe allergic skin rash
  • Severe leg pain or swelling
  • Severe mood swings
  • Two missed periods or signs of pregnancy

You'll need to request a prescription for combination birth control pills from your health care provider. Your health care provider will check your blood pressure and review your medical history, including asking about any medications you're taking.

Your health care provider will also ask about your concerns and preferences to help determine which type of combination birth control pill is right for you. Health care providers generally recommend pills with the lowest dose of hormones that will provide pregnancy protection while also maximizing important noncontraceptive benefits and minimizing side effects.

Although the amount of estrogen in combination pills varies from 20 to 50 micrograms (mcg) of ethinyl estradiol, most pills contain 35 mcg or less. Women who are sensitive to hormones may benefit from taking a pill with a lower dose of estrogen. However, low-dose pills may result in more breakthrough bleeding than may other pills.

Combination pills are categorized based on whether the dose of hormones stays the same or varies:

  • Monophasic. In this type of combination birth control pill, each active pill contains the same amount of estrogen and progestin.
  • Biphasic. In this type of combination birth control pill, active pills contain two different combinations of estrogen and progestin.
  • Triphasic. In this formulation, active pills contain three different combinations of estrogen and progestin. In some types, the progestin content steadily increases — while in others the progestin dose remains steady and the estrogen content increases.

To use combination birth control pills:

  • Consult your health care provider about a starting date. If you use the quick-start method, you can take the first pill in the pack immediately. If you use the Sunday start, you'll take your first pill on the first Sunday following the start of your period. When using the quick start or Sunday start, use a backup method of contraception for the first seven days you take combination birth control pills. If you use the first-day start, you'll take your first pill on the first day of your next period. No backup method of contraception is needed.
  • Pick a time to regularly take the pill. Following a routine may keep you from missing a pill. For maximum effectiveness, you must take combination birth control pills at the same time every day.
  • Follow your health care provider's instructions carefully. Birth control pills only work if you use them correctly, so make sure you understand how you're supposed to use them. If you're using conventional combination birth control pills and want to have regular periods, you will take all of the pills in your pack — the active and the inactive ones — and start a new pack the day after you finish your current one. If you want to avoid monthly periods, ask your health care provider about how to take the pills and how many active pill packs you can take in a row.
  • Be cautious with missed pills. If you miss an active pill, take it as soon as you remember — even if it means taking two active pills in the same day. Take the rest of the pack as usual and use a backup method of contraception for seven days. If you miss more than one active pill, take the last pill you missed right away. Take the rest of the pack as usual and use a backup method of contraception for seven days. If you've had unprotected sex, consult your health care provider about emergency contraception.
  • Don't take breaks between packs. Always have your next pack ready before you finish your current pack.

If you take antibiotics while taking combination birth control pills, use a backup method of birth control. If you vomit within two hours after taking a combination birth control pill or have severe vomiting and diarrhea for two or more days, proceed as if you've missed a pill.

Nov. 18, 2011