For a complete and detailed explanation of how the Birth Control Pill works, we recommend you read
"How the Pill and Other Contraceptives Work" by Chris Kahlenborn, MD. The following is a quick overview of some of the dangers of the Pill, along with direct quotes from the pharmaceutical companies and medical organizations that advocate use of the Pill.
The primary function of the Pill is to prevent ovulation. A woman who does not ovulate will not produce an egg to be fertilized. However, a secondary function of the Pill is to change the lining of the uterus so that if she does ovulate, and the egg is fertilized, the environment becomes too hostile for the fertilized egg to survive. It is this secondary effect that makes the Pill an abortifacient (i.e. a drug capable of inducing an abortion).
For more information, link to these articles:
Breast Cancer: Its Link to Abortion & the Birth Control Pill By Chris Kahlenborn, M.D.
Life Issues Lists several articles related to chemical birth control.
American Life LeaguePharmacists for Life International"Gambling With Life": Chemical Abortion Vital Signs Ministries