The Ethical and Religious Directives are more specific here than on ectopic pregnancy. Directive 36 states:
If, after appropriate testing, there is no evidence that conception has already occurred already, [the female victim] may be treated with medications that would prevent ovulation, sperm capacitation, or fertilization. It is not permissible, however, to initiate or recommend treatments that have as their purpose or direct effect the removal, destruction or interference with implantation of a fertilized ovumWhat does this mean practically? "Appropriate testing" is often taken to mean the Peoria Protocol.** The Peoria Protocol lays out how to tell with moral certainty that a woman has not ovulated and that the primary effect of EC is anti-ovulatory. It involves serum progesterone (<1.5 is pre-ovulatory, okay to give EC) and urine LH (negative is pre-ovulatory, okay to give EC).***
Unfortunately, even if the Peoria protocol can predict the right timing for emergency contraception, it's not clear we have anything to use.
- Hormonal IUDs: insertion of a mirena or skyla as EC relies not only on the anti-ovulatory effects of the levonorgestrel, but also on the intrauterine effects, which act after fertilization. Although it may be argued that application of the Peoria Protocol could allow these effects to be avoided, a systemic hormone (to reach the hypothalamus) is more targeted than an IUD, which would also have to be removed if the patient is later sexually active.
- Paragard: this relies on post-fertilization effects (which is why it works up to five days after the act of intercourse), and cannot be licitly used.
- Plan B: is levonorgestrel, given in one 1.5mg dose or two 0.75mg doses twelve hours apart. Strangely, we can't seem to figure out whether its main effect is primarily anti-ovulatory or post-fertilization. A 2016 review of plan B, done through a Catholic lens as a summary of lots of work by the same authors, found that plan B almost always works through post-ovulatory mechanisms, even when administered before ovulation.
- Ella: ulipristal is a selective progesterone receptor modulator. It is given in one 30 mg dose. It antagonizes progesterone at its receptors on the endometrium, which mean it only has post-fertilization effects. This is the same mechanism of action as mifepristone (RU486, which is given in doses of 600mg for elective abortions). Although package inserts deny that it is abortifacient, this indicates that a 30mg dose is not suspected to have post-implantation effects. For a Catholic who understands life to begin at sperm-egg fusion, ulipristal is extremely likely to lead to loss of embryonic life.
- Hormonal pills: these may be licit before ovulation (still need the Peoria protocol), used in a Yuzpe-like regimen, so that there's enough estrogen to actually act as an anti-ovulant. More research needed!
- Meloxicam: this COX-2 inhibitor can, at doses of 30 mg/day taken for five days during the late follicular phase and the day of the LH surge, prevent functional ovulation in 90% of women with no effect on LH, progesterone, estradiol levels, or cycle length. There are concerns that NSAIDs disrupt implantation. Jury's still out, but this seems the most defensible option at this time. It relies on a hospital's ability to identify the follicular phase/LH surgr (a.k.a. you need the Peoria protocol).
*I wrote the first draft of this post on a month of nights my intern year. By the time I got back to it to revise it, I was on a month of nights during my second year. Wow.
**A complete moral explanation supporting the Peoria protocol can be found in Slosar JP. Catholic health care and emergency contraception. Healthcare Ethics:2000;8,4. (No link available.)
***Notice I didn't give units. Do not use cutoffs in a blog post to determine management of patients requesting EC. You need a working relationship with your hospital lab and you need to be better acquainted with the Protocol's other reference ranges for progesterone before you can use it.