Levonorgestrel
"Took Plan B on April 13, 27, and 30th. Almost didn't take it the third time, but the nurse practitioner assured me that (despite controversy about the issue) this would be fine. It's certainly better than being pregnant. 



I've never had any noticeable side-effects from taking Plan B. Perhaps moodiness, but it's difficult to attribute the origin of moodiness. My period also came a week early. Again: way, way better than being pregnant."