Combination birth control pills are a reliable form of contraception that's easily reversed. Fertility can return almost right away after you stop taking the pills.

Along with preventing pregnancy, other benefits of these pills include:

• Lower risk of cancer of the ovaries and the lining of the uterus, ectopic pregnancy, ovarian cysts, and noncancerous breast disease
• Improvement in acne and excessive face and body hair
• Less severe menstrual cramps, called dysmenorrhea
• Reduced androgen production caused by polycystic ovary syndrome
• Decreased heavy menstrual bleeding from uterine fibroids and other causes, as well as a decrease in iron deficiency anemia related to blood loss
• Treatment of premenstrual syndrome (PMS)
• Shorter, lighter periods on an expected schedule or, for some types of combination pills, fewer periods yearly
• Better control of the monthly cycle and fewer hot flashes during the time when the body makes the natural transition to menopause, called perimenopause

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

• Conventional pack. One common type contains 21 active pills and seven inactive pills. Inactive pills do not contain hormones. Formulations containing 24 active pills and four inactive pills, known as a shortened pill-free interval, also are available. Some newer pills may contain only two inactive pills.

  You take a pill every day and start a new pack when you finish the old one. Packs usually contain 28 days of pills. Bleeding may occur every month during the time when you take the inactive pills that are at the end of each pack.

• Extended-cycle pack. These packs typically contain 84 active pills and seven inactive pills. Bleeding generally occurs only four times a year during the seven days you take the inactive pills.
• Continuous-dosing pack. A 365-day pill also is available. You take this pill every day at the same time. For some people, periods stop altogether. For others, periods become significantly lighter. You do not take any inactive pills.

By decreasing or stopping periods, continuous-dosing and extended-cycle pills might have other benefits. These can include:

• Preventing and treating heavy bleeding related to uterine fibroids.
• Preventing menstrual migraines.
• Lessening the worsening effect menstruation can have on certain conditions, including seizures.
• Relieving pain related to endometriosis.

Combination birth control pills aren't the best choice for everyone. Your health care provider might suggest that you use another form of birth control if you:

• Are in the first month of breastfeeding or first few weeks after giving birth.
• Are older than 35 and smoke.
• Have poorly controlled high blood pressure.
• Have a history of or current blood clots, including in your legs — called deep vein thrombosis — or in your lungs — called pulmonary embolism.
• Have a history of stroke or heart disease.
• Have a history of breast cancer.
• Have migraine with aura.
• Have diabetes-related complications, such as kidney disease, eye disease or problems with nerve function.
• Have certain liver and gallbladder diseases.
• Have unexplained uterine bleeding.
• Will be confined to bed for an extended period of time after surgery or an injury or during a serious illness.

Pregnancy

Based on typical use, about 9 out of 100 people taking combination birth control pills will get pregnant in the first year of use. With perfect use as directed, the pregnancy rate is less than 1 in 100 people every year.

Although taking combination birth control pills during early pregnancy doesn't increase the risk of birth defects, it's best to stop using the pills as soon as you suspect you're pregnant.

Sexually transmitted infections

Combination birth control pills won't protect you from sexually transmitted infections. To help protect against these infections, practice safer sex.

Side effects

Combination birth control pills can cause side effects such as:

• Bleeding while taking the active pills — called breakthrough bleeding or spotting — that is more common with continuous-dosing or extended-cycle pills.
• Breast tenderness.
• Headaches.
• Nausea.
• Bloating.
• Increased blood pressure.

Some side effects — including nausea, headaches, breast tenderness, bloating and breakthrough bleeding — might get better after you've taken the pill for a while.

Possible risks

Combination birth control pills increase the risk of certain conditions, which can be serious. They include:

• Blood clots in the legs, called deep vein thrombosis.
• Heart attack and stroke, especially if you smoke.
• Liver disorders.

When to call your doctor

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

• Belly pain, cramping and vomiting.
• Chest pain, coughing and trouble breathing.
• New or worsening headaches, difficulty speaking, confusion, blurred vision, or loss of vision.
• Severe pain, change in skin color and swelling in a leg.
• Depression or severe mood swings.
• Jaundice, which is yellowish discoloration of the skin and eyes.
• Two missed periods or symptoms of pregnancy.

You'll need to request a prescription for combination birth control pills from your health care provider. Your provider measures your blood pressure, checks your weight, and talks with you about your health and any medicines you're taking.

Your provider also asks about your concerns and what you would like from your birth control to help figure out which combination birth control pill is right for you. Health care providers often recommend pills with the lowest dose of hormones that will help prevent pregnancy, give you important benefits other than birth control and cause the fewest side effects.

Although the amount of estrogen in combination pills can be as low as 10 micrograms (mcg) of ethinyl estradiol, most pills contain about 20 to 35 mcg. Low-dose pills can result in more breakthrough bleeding than can pills with more estrogen. Some combined oral contraceptives contain other types of estrogen.

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

• Monophasic. Each active pill contains the same amount of estrogen and progestin.
• Biphasic. Active pills contain two combinations of estrogen and progestin.
• Triphasic. Active pills contain three combinations of estrogen and progestin. In some types, the progestin content increases; in others, the progestin dose remains steady and the estrogen content increases.

To begin a combined oral contraceptive, talk to your health care provider about a starting date:

• Quick-start method. You can take the first pill in the pack right away.
• Sunday-start method. You take your first pill on the first Sunday after your period starts.
• First-day-start method. You take your first pill on the first day of your next period.

With quick-start or Sunday-start methods, use a backup contraception method, such as a condom, for the first seven days you take combination birth control pills.

For the first-day-start method, no backup method of contraception is needed.

To use combination birth control pills:

• Pick a time to take the pill every day. Combined oral contraceptives need to be taken every day to be effective. Following a routine might keep you from missing a pill and help you take the pill at the same time every day. For example, consider taking your pill when you brush your teeth in the morning.

• Follow your health care provider's instructions carefully. Birth control pills only work if you use them correctly, so make sure you understand the instructions. Because there are many different formulas of combined oral contraceptives, check with your health care provider about specific instructions for your pills.

  If you're using the conventional type of 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, continuous-dosing or extended-dosing options reduce the number of periods in a year. Ask your health care provider about how to take the pills and how many active pill packs you take in a row.

• Know what to do when you miss pills. If you miss one 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. Use a backup method of contraception for seven days if you missed your pill by more than 12 hours.

  If you miss more than one active pill, take the last pill you missed right away. Take the rest of the pack as usual. Use a backup method of contraception for seven days. If you've had unprotected sex, you may consider emergency contraception.

• Know what to do if you lose or miss pills due to vomiting. If you vomit within two hours after taking a combination birth control pill or have severe vomiting and diarrhea for two or more days and can't take the pills, follow the instructions in the same way you would if you missed one or more pills.
• Don't take breaks between packs. Always have your next pack ready before you finish your current pack.

Talk to your health care provider to decide if combination birth control pills are right for you. Also talk to your provider if you have any concerns or if you'd like to change to another method of birth control.