What are the different kinds of birth control pills?

There are two main kinds of birth control pills:

• Combination birth control pills. This type of pill contains both estrogen and progestin. There are a wide variety of combination pills to choose from, depending on how often you want to have periods and the dose of hormones that is best for you.
• The minipill. This type of pill contains only progestin. The minipill doesn't offer as many choices as combination pills. In each pack of pills, all the pills contain the same amount of progestin and all the pills are active. The progestin dose in a minipill is lower than the progestin dose in any combination pill.

Combination birth control pills come in different mixtures of active and inactive pills, depending on how often you want to have periods:

• Conventional. Conventional packs usually contain 21 active pills and seven inactive pills, or 24 active pills and four inactive pills. Bleeding occurs every month when you take the inactive pills.
• Continuous dosing or extended cycle. These packs typically contain 84 active pills and seven inactive pills. Bleeding generally occurs only four times a year, during the time when you take the inactive pills. Formulations that contain only active pills — eliminating bleeding — also are available.

Combination birth control pills are also categorized according to whether the dose of hormones in the active pills stays the same or varies:

• Monophasic. In this type of combination birth control pill, each active pill contains the same amounts of estrogen and progestin.
• Multiphasic. In this type of combination birth control pill, the amounts of hormones in active pills vary.

Most combination birth control pills contain 10 to 35 micrograms of ethinyl estradiol, a kind of estrogen. Women who are sensitive to hormones may benefit from taking a pill that contains a dose of estrogen at the lower end of this range. However, low-dose pills may result in more breakthrough bleeding — bleeding or spotting between periods — than higher dose pills.