Learning About Birth Control Pills
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Learning About Birth Control Pills

rerun image More than 10 million women in the US use birth control pills, also known as "the Pill", according to a spokesperson for Planned Parenthood. Although women are grateful for this relatively simple and reliable form of contraception, most of them readily admit that they don't know much about how oral contraceptives actually work.

"A 'false pregnancy' was the old way of describing how birth control pills work, and that's still what many people say," says James McCarrick, MD, PhD, an obstetrician and gynecologist with the Palo Alto Medical Foundation. "But that's not accurate."

McCarrick explains that the "waxing and waning"of women's hormone levels causes the ovulation cycle. Birth control pills provide a steady level of hormones, and this steady hormonal state suppresses ovulation.

So Many Choices

"The majority of women could use any oral contraceptive and be fine in terms of preventing pregnancy," McCarrick says. "There are dozens of effective brands out there." Most birth control pills contain two hormones, estrogen and progestin.


The same kind of estrogen is in "all the low-dose pills, which 99.99% of [Pill-taking] women in the United States use," says Cheryl Walker, MD, assistant professor of gynecology and obstetrics at Stanford University Medical School. Walker says low-dose estrogen pills contain 20, 30, or 35 micrograms (mgs) of estrogen. The exact dose of estrogen may have an impact on the kind of side effects you experience.

Some women should not take pills with estrogen, McCarrick advises. Women who are breastfeeding, have a history of blood clots, or have high blood pressure may be better off with a progestin-only pill, which has a slightly lower efficacy level than the combination pill.


Different brands of the Pill may contain one of five progestins, says Walker. Because women differ in the kind of progestin found naturally in their bodies, McCarrick says, one variety of progestin can have different side effects on different individuals.

Monophasic vs. Triphasic

Within the family of estrogen-containing pills, there are two main types: monophasic and triphasic. As the names suggest, monophasic pills provide the same level of hormones throughout the pill cycle. Triphasic pills also induce a steady state of hormones, but at three different levels during the cycle. McCarrick says the preference for monophasic vs. triphasic pills lies with the individual, and he stresses that the two types are equally effective for pregnancy prevention.

"Work with your doctor to figure out which one might be right for you," suggests Holly Hughes, RN, a staff nurse at the Brigham Ob-Gyn Group in Boston. "Just because someone else had a great experience with a certain kind of pill doesn't mean you will."

Fewer Side Effects Today

"There are fewer side effects now than there used to be because oral contraceptives today contain a much lower level of estrogen," says McCarrick, who adds that the hormone levels in pills of yesteryear were "five to twenty times greater than what they are today." Lower hormone levels usually mean fewer side effects, but side effects do still occur.

Negative Side Effects

"The most common complaint I get is about breakthrough bleeding, which can be annoying," says Hughes. But, she reminds new pill-takers, "You are changing your hormone levels, so give a new type of pill at least three months while your body adjusts."

Other possible side effects include headaches, nausea, breast tenderness, and bloating. If the negative side effects last for more than three months, talk to your doctor and consider changing brands.

Positive Side Effects

Many people experience skin improvements. For example, particular types of the Pill may improve acne. Also, use of the pill decreases a woman’s risk for subsequent ovarian and endometrial cancer.

"I talk to my patients about the symptoms they are most concerned about and try to prescribe a kind of pill that will minimize those symptoms," McCarrick says. But because of individual differences you can never be sure, he says. "If you try one and it's not right for you, there are plenty of other options to try."

Your Period on the Pill

If, like many women, your monthly pill pack contains three weeks worth of active pills and one week of placebo pills, you have what seems like your period every month. "It's actually not a period; it's a bleeding event that occurs because you stop taking hormones," says McCarrick. Because ovulation has been suppressed for three weeks, you won't ovulate during that week. However, "If you waited 10-14 days before resuming taking active pills, your body would get ready to ovulate again."

You can decide to skip the placebo pills and continue taking active hormones, in which case you won't bleed each month. "That's a great option. You can tailor your pill schedule to fit your lifestyle," Walker says. "But you should try to bleed at least every three months or you may experience some discomfort," she adds.

Oops, I Skipped a Day…

Taking a week off after three weeks of active hormones is part of a normal pill cycle, but skipping days in the middle of the three weeks is not a good idea. "If you have been taking active pills for four months and you miss a day or two, you won't ovulate," McCarrick says. But he says that if you skip a couple days in the middle of only three weeks of suppression, "you could have breakthrough ovulation."

When you take oral contraceptives, the hormone thins out the lining of the uterus making it unable to host egg implantation, and the mucus in the cervix thickens, making it tough for sperm to swim through. According to Walker, these benefits go away if you miss a day, increasing your risk for pregnancy.

If you do miss a pill, take it that day as soon as you remember. Or double up (take two pills) if you don't remember until the next day. Walker recommends using another method of contraception for at least two weeks if you do skip an entire day. If you forget to take your pill for more than a day consult your doctor for directions. Complete directions for what to do are also included under the patient package-insert instructions that come with your birth control pill.

Talk to Your Doctor

You can't get birth control pills without a prescription, so you have to see a doctor at some point. Be open with your doctor so that you can make the best decision possible about birth control pills. Women with certain conditions should not take oral contraceptive. McCarrick reminds women to tell their doctors about any medications they take. "Don't just tell your doctor about your prescription medications," he says. "Mention any over-the-counter or herbal medications, too, because they might have an interaction with your pills."

All birth control pills on the US market "are effective and safe," Walker says. "If you are on a particular brand and you're happy, don't change it," she adds. But if you experience problems and side effects, speak up. There may be something out there that's better for you.


American College of Obstetricians and Gynecologists


Planned Parenthood


The Canadian Women's Health Network

The Society of Obstetricians and Gynaecologists of Canada


American College of Obstetricians and Gynecologists website. Available at: http://www.acog.org/publications/patient_education/021.cfm. Accessed June 20, 2008.

American College of Obstetricians and Gynecologists. Prophylactic oophorectomy. Practice Bulletin. No 7. September 1999.

Last reviewed June 2008 by Ganson Purcell Jr., MD, FACOG, FACPE

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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