Birth control pills, (also known as 'the Pill'), are made of fake, or synthetic, hormones (estrogen and progesterone) that stop a female from releasing an egg, aka, "ovulating." They also thicken the mucus on the cervix, which makes it difficult for sperm to get through. With no egg, there can be no pregnancy. A birth control pill must be taken every day, at about the same time, in order to work. If you miss a pill or take them at different times on different days, they will be less effective.

Your doctor will explain when your pills become effective at preventing pregnancy. Generally, pills become effective in one week. If you are ever unsure when your pills become effective use condoms as back-up.

When used perfectly - taken every day at around the same time - it prevents pregnancy 99.7 percent of the time. Add in human error—missing a day or taking them at different times—that rate drops to 92 percent.

Birth control pills sometimes have side effects, both good and bad. They include slight weight gain or loss, lighter periods, preventing or lessening menstrual cramps, less acne, a change in appetite, mood swings, bleeding between periods, and changes in your sex drive. For most girls, annoying side effects are gone within three months of beginning the Pill. Birth control pills can increase a woman's risk of more serious side effects, such as blood clots. However, these are extremely rare among teens. The Pill offers NO protection against sexually transmitted diseases, so you need to also use a condom whenever you have sex.

You also need a prescription from a health care provider to get the Pill. The cost varies, depending on where you go to get a prescription. Typically, you'll pay less if you go to a family planning clinic, like Planned Parenthood ($5-$40 per month), versus a drug store. However, it really depends on whether or not you have health insurance. When you call to make the appointment, be sure to ask.

For more information, click "the Pill," or you can call the Sex Information Line at 1-888-30-SX-ASK (307-9275).