The American Academy of Pediatrics has recommended that pediatricians begin prescribing Plan B ahead of time (where by “time” I mean “intercourse”) to women under 17, due to the difficulties teen girls often face in obtaining the drug:
A 2010 analysis of seven randomized studies of emergency contraception found that having a morning-after prescription in hand did not increase teens’ sexual activity or decrease use of standard contraceptives but did increase use of the pill and shorten the time before a teenager used it after sex.
I know I say this nearly every time I mention Plan B, but it does not cause abortions or prevent implantation.