There are several different types of birth control pills. Some of them use a combination of the hormones progestin and estrogen, while others contain progestin only. Some birth control pills can be used after intercourse as emergency conception, or "morning after" pills, as well as before intercourse occurs to prevent pregnancy. Some contain a reduced dose of hormones.

Combination of Progestin and Estrogen in Birth Control Pills

Birth control pills which contain both progestin and estrogen in combination are usually sold in kits containing a month's supply of 28 pills, 21 of them active with the hormones, and 7 of them placebos or "reminder pills." Or these seven pills can contain a lower dose of the hormones. Some birth control pills contain progestin only. These can be taken all 28 days of the cycle. Reminder pills are not necessary. Different kinds of pills can contain different forms of estrogen and progestin, as well as different amounts. Even within a 28-day supply of one particular brand, pills with different amounts and proportions of the two hormones could be assigned to different days. One brand is used on a 24-4 basis rather than the usual 21-7. To work properly, each dose should be taken at the same time every day whether intercourse is anticipated or not. If a dose is skipped and intercourse occurs, it may be necessary to take emergency contraception after the intercourse.

Emergency Conception Pills

Also known as "morning after" pills, these help reduce the likelihood of pregnancy when taken within 5 days after intercourse occurs, as opposed to the other birth control pills which are taken before intercourse to prevent pregnancy. The sooner after intercourse the emergency conception is taken, the more effective it is in preventing pregnancy. These pills are most effective when taken during the first 72 hours after intercourse. Many regular birth control pills can also be used in the same way as emergency conception. If used in this way, they are taken in two increased doses, one hour apart. The exact number of the active hormonal pill depends on the instructions for each particular pill, but the most common number of pills used in each of the two doses is five pills at the same time. Emergency conception is not as effective as preventive birth control, but could be necessary after unprotected sex when the woman was not prepared for the intercourse with adequate birth control measures in place.

Low Dose Birth Control Pills

Low dose birth control pills have less than the usual amount of progestin and/or estrogen to make them safer from serious side effects in older women who are already having hormonal imbalances due to menopause.