All contraceptive acts (e.g. taking a birth control pill), and all contracepted sexual acts (e.g. choosing to engage in sexual acts not inherently ordered toward procreation) are intrinsically evil because they are the deliberate choice of an act that is inherently directed at a moral object deprived of a good (the procreative meaning) required by the eternal moral law. The use of contraceptives is intrinsically evil because sexual relations is inherently directed at conception.
Consider that withdrawal is one type of immoral contraception (cf. Gen 38:9). But if someone interrupts a rape that is in progress, this interruption of the rape is moral. The interruption of the sexual act of rape does not constitute the withdrawal method of contraception because the contraceptive effect is not the moral object, but an effect in the consequences of the act. The moral object of the interruption is to end an injustice to one’s neighbor; as an act of love of neighbor, interrupting a rape in progress has a good moral object. And in the third font, the good consequence of stopping an act of severe physical, emotional, and mental harm outweighs the bad consequence of the contraceptive effect.
Similarly, after a rape is completed, if a women enters a hospital emergency room and is given a non-abortifacient spermicide, this medical intervention has the moral object of interrupting the rape. For conception is the natural and inherent aim of sexual intercourse. Therefore, this medical intervention is inherently directed at interrupting a rape, and the contraceptive effect is in the third font, not the second font. Thus, a non-abortifacient intervention to prevent conception in cases of rape does not meet the definition of contraception in moral terms. Every physical act of natural intercourse, even a rape, naturally progresses toward conception because the sexual faculty was designed for that purpose. And so the use of an intervention, what would ordinary be called a contraceptive, to prevent conception after a rape is an interruption of the rape itself. In terms of the moral analysis of the second font, this intervention is similar to indirect abortion and indirect sterilization, and so it might be termed ‘indirect contraception.’
It is moral to interrupt a rape, because the act of interrupting is not a contraceptive act, but a moral act based on the positive precept requiring one to assist a neighbor in need. Since sexual intercourse is inherently aimed at conception, an intervention to prevent conception in cases of rape is an interruption of the rape (in terms of morality) and is therefore not a morally direct act of contraception. For the progress toward conception is a continuation of, and an inherent part of, the act of sexual intercourse (which in this case is also rape). Therefore, such an intervention (e.g. use of spermicides) is not contraception per se and is moral, as long as the intervention is not abortifacient.
An abortifacient cannot be used in such a case. Once a new human life begins, the direct and voluntary killing of that innocent human person is intrinsically evil and always gravely immoral. And conception is, in a sense, the completion of the sexual act. Killing a child conceived by rape does not interrupt the rape, but rather represents a second and more serious crime after the rape, the crime of murder.
A woman who has been raped might have previously conceived a child by her husband. Medical tests for pregnancy are only able to detect pregnancy about 2 or 3 weeks after conception. So it is possible that a woman who tests negative for pregnancy might still have conceived a child by her husband, prior to the rape. Or, if there is some length of time before the woman obtains medical help, she may have conceived a child from the rape. In either case, the new human life deserves the full protection due to any innocent human person. And so an abortifacient contraceptive must not be used in order to interrupt the rape, due to the significant risk that a prenatal might have been conceived and might be killed.
However, if the physician can be morally certain that the contraceptive will not act as an abortifacient in any particular case, a drug that has a contraceptive effect is moral to use.
Contraception is intrinsically evil and always gravely immoral, because sexual intercourse is inherently aimed at conception. But for the same reason, the use of an intervention to prevent conception in cases of rape is not direct contraception. The progress toward conception is an inherent part of the rape, and so it is moral to interrupt the rape with an intervention to prevent conception.