First, the teenager girl’s intentions are of great importance here. If she was truly to be doing these things purely for health reasons (and in USA…she shouldn’t be drinking at that age as it is illegal). Than she would not be conciously attempting a miscarriageat face value. However, it is highly unlikely that these things could be done without someone (particullarly her OBGYN/Doctor) telling her not to do them or she would be risking loosing her child. At this point she would have to make a moral decision regarding this threat. I’m assuming that you are implying that she is choosing these activities hoping for a miscarriage … in otherwords, she is intentionally attempting to end a life.
First and foremost, in the case of NFP, the issue of killing a human being does not come into play. That being said, this comparison does not really relate to any moral issue that could be present in the practice of NFP. However, for the sake of argument.
First we must clarify what form of ABC is used. Though, admittedly all are an afront against life, some are abortifacients -actually killing a life. This would relate to the presented scenerio, and the difference between abortifacients and NFP should be easily recognized.
In the case of non-abortifacient ABC - such as condoms - a different principle is involved. We must take into account the role of intercourse within a marriage - it is to be both procreative and unitive. Condoms interfere with both aspects of this. It is not procreative for obvious reasons. It is not unitive because it is accepting intercourse only partially. (see Theology of the Body, Humanae Vitae, or a book/DVD/CD by Christopher West for a more complete explanation).
A few differences:
NFP can be used to both help conceive a child and to prevent conception during times when serious reasons exist to do so (emphasis on the necessity of serious reasons). Under no circumstances can ABC be used to help concieve. NFP uses abstinence to prevent conception (which we participate in for the majority of our day anyway :D). In addition, NFP encourages spouses to be open about their sexuallity (through charting), continually provides the opportunity to discuss the possibility of when children would be able to be concieved. It also helps to curb lust in intercourse and focus on recognizing God as a participant in intercourse.
At this point, others will have to finish off…baby calls.