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A 'Plan B' pill primer for parents

A package containing a Plan B One-Step tablet,

A package containing a Plan B One-Step tablet, often known as the "morning-after pill." Credit: AP/eva Women's Health

Q. When a teenager takes the Plan B "morning after" pill to prevent pregnancy, what is it doing to her body?

A. The Plan B emergency contraception pill has been in the news recently as branches of government argue over the age girls should be allowed to buy it without a prescription or identification.

The one-dose pill contains 1.5 milligrams of levonorgestrel, the same progesterone hormone in some birth control pills, says Dr. Elisa Felsen-Singer, an obstetrician and gynecologist at the Huntington Medical Group. It's most effective within 24 hours of unprotected sex.

The hormone can delay ovulation long enough for sperm to become ineffective, which can take up to five days. It also temporarily alters the uterine environment, making it challenging for sperm to swim to an egg and perhaps more difficult for a fertilized egg to attach to the uterus lining, she says.

"It's not an abortion pill. It doesn't cause miscarriage. It will not stop the development of a fetus once a fertilized egg has implanted in the uterus," Felsen-Singer says. If a woman is already pregnant, it won't harm the fetus, she says.

Side effects can include nausea, fatigue, headache, dizziness, breast tenderness, abdominal pain and bleeding before the period. There are no known long-term effects, she says.

Felsen-Singer has a teenage daughter. "If my daughter came to me tonight and said, 'I had unprotected sex,' the first place I would be is CVS," Felsen-Singer says. "From a safety perspective, I would be very comfortable."

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