How Effective Are Birth Control Pills?

How Effective Are Birth Control Pills?

Effectiveness is an important and common concern when choosing a birth control method. Birth control pills are very effective. Combination pills work best when taken every day. Progestin-only pills must be taken at the same time every day. That keeps the correct level of hormone in a woman’s body.

• Less than 1 out of 100 women will get pregnant each year if they always take the pill each day as directed.
• About 9 out of 100 women will get pregnant each year if they don’t always take the pill each day as directed.

The pill may be slightly less effective for women who are very overweight. Talk with your health care provider if you are concerned about how well the pill may work for you.

Certain medicines and supplements may make the pill less effective. These include

• the antibiotic rifampin — other antibiotics do not make the pill less effective
• certain medicines that are taken by mouth for yeast infections
• certain HIV medicines
• certain anti-seizure medicines
• St. John's wort

Vomiting and diarrhea may also keep the pill from working. Ask your health care provider for advice. Use a backup method of birth control — like a condom, female condom, diaphragm, sponge, or emergency contraception (morning after pill) — until you find out you don’t need to.

Keep in mind the pill doesn’t protect against sexually transmitted infections. Use a latex or female condom to reduce the risk of infection.