Can a married Catholic woman take the birth control pill, if it is prescribed by her physician to treat a medical problem?
If she refrains from marital relations, she can take the pill for a medical purpose. Absent sexual relations, the act of taking this type of pill does not have contraceptive or abortive ends.
However, she cannot BOTH choose to take this type of medication AND continue to have marital relations. Taking the birth control pill while sexually active deprives the sexual acts of the procreative meaning. This type of pill is also an abortifacient, meaning that if conception should occur, the pill can prevent implantation, resulting in an early abortion. Contraception and abortion are both intrinsically evil and gravely immoral acts.
Intrinsically evil acts are never justified by intention or circumstances. So we cannot say that the deprivation of the procreative meaning or the deaths of these innocent prenatals is somehow justified. And the principle of double effect does not apply, since that principle specifies that the act cannot be intrinsically evil.