There are three different types of birth control pills, also known as oral contraceptives, on the market today: the combination pill, the mini-pill and the emergency contraceptive pill.

Combination pill
This pill, which contains the hormones estrogen and progestin, is the most widely prescribed. It works by suppressing ovulation each month. By thinning the uterine lining and changing the consistency of the mucus in a woman's cervix, it also makes it harder for sperm to move into contact with an egg.

There are different formulations. Some require a 21-day regimen followed by one week of placebo tablets. Others vary the dose of estrogen and/or progestin that a woman gets throughout her cycle, or add five additional estrogen pills at the end of the 21-day cycle. But all of today's pills contain far less estrogen than their older counterparts.

In 2007, the FDA approved Lybrel, the first continuous use birth control pill. It is a multiphasic pill (containing varying levels of estrogen and progestin designed to be taken at specific times throughout the entire pill-taking schedule) and comes in a 28-day pack. This product is designed to be taken continuously, which means you won't have a period, although you may have some spotting or breakthrough bleeding.

There are no long-term fertility effects associated with birth control use.
One caveat: Some medications, including antibiotics, anticonvulsants and herbal products like Saint Johnswort which may help relieve mild depression can reduce the effectiveness of the pill.