Plan B emergency contraception is available over-the-counter and used by thousands of women a year. But does taking it increase a woman’s risk of cancer?

Millions of women have taken Plan B, a form of emergency contraception; it has become even more popular in the decade-plus that it has been available without a prescription. The single-dose pill is used to prevent pregnancy and is 95 percent effective when taken within 24 hours of having unprotected sex and 89 percent effective when taken within three days.

Plan B contains a high dose of levonorgestrel, a synthetic form of the hormone progesterone. It wards off pregnancy by preventing ovulation, interfering with the fertilization process and/or preventing a fertilized egg from implanting in the lining of a woman’s uterus.

According to the U.S. Centers for Disease Control and Prevention, between 2006 to 2010, of sexually active women between the ages of 15 and 44, 11 percent (5.8 million women) had taken the morning-after pill, and of those women, 59 percent had used it once and 4 percent twice.

So, does Plan B increase a woman’s risk of cancer?

There have not been any studies focusing specifically on Plan B and a woman’s risk for cancer. There have been numerous studies looking at a woman’s cancer risk and the use of birth control pills.

Before we look at those risks in-depth, it’s important to remember that some birth control pills contain progestin and estrogen, while Plan B only contains progestin. Also, birth control pills are typically used on an ongoing basis, sometimes for many years, whereas Plan B is not intended to be used regularly.

Oral contraceptives and breast cancer risk

A review of 54 studies, conducted by Collaborative Group on Hormonal Factors in Breast Cancer in 1992, showed that women who took birth control pills had a slightly higher risk of breast cancer than women who had never taken the pill. But 10 years after the women stopped taking birth control pills, their increased risk disappeared.

Oral contraceptives and cervical cancer risk

Women who take birth control pills are more likely to be infected with human papillomavirus (HPV), according to an analysis of studies conducted by the International Agency for Research on Cancer, part of the World Health Organization. The risk was highest in women who had used the pill for 10 years or more.

That said, HPV almost always is contracted as a result of having sex with an infected partner and isn’t likely a direct result of the hormones in the pill, reports the National Cancer Institute. As with breast cancer, the increased risk decreases over time after a woman stops taking birth control pills.

Oral contraceptives and liver cancer risk

Women who take the pill may have an increased risk of benign liver tumors. These tumors rarely become cancerous but may rupture or bleed, one study found.

Oral contraceptives and cervical cancer risk

Birth control pills have been shown, in fact, to lower a woman’s risk for cervical cancer. Some studies suggest that progestin-only pills have a better effect than combination pills. The longer a woman takes oral contraceptives, the lower her risk is, so a woman taking Plan B only once is unlikely to see any benefits.

Oral contraceptives and endometrial cancer risk

The pill has been shown to lower a woman’s risk of endometrial cancer; the longer she takes it, the longer her risk is lowered.

The final word: Currently, there is no conclusive evidence suggesting Plan B increases or decreases a woman’s risk of cancer. Groups including the American Medical Association, American College of Gynecologists and the American Academy of Pediatrics have deemed it safe and effective when used as intended.

If you find that you are relying on Plan B as your main form of birth control, speak to your gynecologists about your options. It is not as effective at preventing pregnancy as other birth control methods, is costlier and may have more side effects than other forms of birth control when used frequently.

“Plan B, or Plan B One-Step, are associated with nausea in about 10 percent of people and irregular bleeding,” said Sharon Orrange, MD, clinical associate professor of medicine at Keck School of Medicine of USC and primary care physician at Keck Medicine of USC. “Plan B has not been shown to increase the risk of any form of cancer.

“It is important to know that levonorgestrel (Plan B or Plan B One-Step) may be less effective or not effective in overweight and obese women,” Dr. Orrange added. “Studies suggest that Plan B may be less effective as an emergency contraceptive in women 165 to 176 pounds (75 to 80 kg) and not effective in women over 176 pounds (over 80 kg).”

If you are local to Southern California and are in search of a primary care physician, call (800) USC-CARE (800-872-2273) or visit www.keckmedicine.org/request-an-appointment/ to schedule an appointment.

By: Anne Fritz