Birth-control pills, or oral contraceptives, are taken by mouth every day to prevent ovulation. Most women take the combination pill, which contains two hormones, estrogen and progestin. The mini-pill, on the other hand, contains only progestin. Birth-control pills need to be taken at about the same time every day.

In addition to their effects on ovulation, these contraceptive pills thicken the mucus secreted by the cervix. This slows the movement of sperm traveling from the vagina toward the uterus and fallopian tubes.

Combination birth-control pills need to be taken daily. If more than two pills are missed, then it is best to stop taking the pill for that month, allow menstruation to take place, and start a new pack with your next menstrual cycle. A back-up method, usually condoms or abstinence, should be used during this time to prevent pregnancy.

Mini-pills are more sensitive to missed or delayed doses because each dose protects for just 24 hours. A back-up birth-control method is necessary for at least two days if you miss a dose (even if it is delayed by only three hours).

When used correctly, birth-control pills are 97 percent to 99 percent effective in preventing pregnancy.

Advantages

• Protection is provided around the clock as long as the pills are taken correctly.
• Regular use of birth-control pills decreases menstrual flow and shortens the length and pain of menstruation.
• Birth-control pills also allow sexual intercourse to be spontaneous in that they provide 24-hour protection if used appropriately.
• Birth control pills offer many additional benefits, including a decreased risk of ovarian and uterine cancer, non-cancerous breast disease, iron deficiency anemia, and for some types of pills, improvement in acne.

Disadvantages

• A health care professional must prescribe birth-control pills.
• The main drawback is remembering to take the pill at the same time every day, as prescribed. This will minimize irregular vaginal bleeding, and maximize the effectiveness in preventing pregnancy.
You must wait one to three months after stopping birth-control pills for your natural, regular menstrual cycle to resume. The effects of the pill usually wear off within a week or so after you stop taking the pill but it still may take a couple of months before your regular menstruation returns.
• Hormonal methods thicken cervical secretions and trap bacteria but they cannot protect the outer genital skin and vagina against viral or bacterial infections. This means that you are still at risk of sexually transmitted diseases.
• Women who have a history of breast cancer, liver disease, undiagnosed abnormal uterine bleeding, high blood pressure, blood-clotting disorders, or stroke should not take oral contraceptives. Smokers over the age of 35 should also avoid this type of birth control.
• Oral contraceptives have important interactions with some seizure drugs, antibiotics, antifungal agents, and other medications, decreasing the birth control effectiveness. You should talk to your doctor or pharmacist to be sure that other medications you are taking will not decrease the effectiveness of your birth-control pills.