Is it true, as some claim, that some methods of birth control can cause an abortion?

Some methods of birth control are aimed at preventing the union of sperm and egg and therefore act only as contraceptives. These would include barriers such as condoms and diaphragms. By contrast, hormonal methods such as the Pill may work in several ways. They can suppress ovulation or alter cervical mucus to prevent fertilization, and thus act contraceptively. But they may at times have other effects, such as changes to the lining of the uterus.

If the contraceptive action fails and fertilization takes place, these hormonal methods may make it impossible for a newly conceived life to implant and survive. That would be a very early abortion. Medical opinions differ on whether or how often this may occur.

Currently there is no way to know precisely how these drugs work at any given time in an individual woman. Concern about the risk of causing an early abortion is stronger in the case of pills taken after intercourse to prevent pregnancy (“emergency contraception” or “morning-after pills”). In some cases these pills are taken when sperm and egg have already joined to create a new life, in which case the drug could not have any effect except to cause an early abortion.