I mentioned before that mifepristone (Mifeprex) is not an "abortion pill", but rather an antiprogesterone one: depending on dosage/regimen, it can either prevent or terminate a pregnancy.
An UK study reports that taking 10 mg of mifepristone up to five days after having unprotected sexual intercourse works as well as the double-dose levonorgestrel [Plan B] regimen (one 0.75 mg dose, followed by a second dose, 12 hours apart):
When taken within five days after unprotected sex, mifepristone works as well for emergency contraception as the approved drug levonorgestrel, UK researchers report.
In a study involving about 2000 women, Dr. Haitham Hamoda of the University of Aberdeen and colleagues compared the efficacy, adverse effects, and acceptability of a single 10-milligram dose of mifepristone with two 750-microgram doses of levonorgestrel 12 hours apart. The agents were taken within 120 hours of unprotected sexual intercourse
The failure rates were 1.5 percent with mifepristone and 2.3 percent with levonorgestrel -- not a statistical difference -- the investigators report in the medical journal Obstetrics and Gynecology. However, also statistically, they could not rule out the possibility that levonorgestrel might be less effective than mifepristone.
Acceptability was high. In total, 94 percent of the mifepristone group were satisfied, as were 91 percent of the levonorgestrel group.
Important Note: You can take both levonorgestrel doses at the same time.
In other words, you can take the entire 1.5 mg dose (two Plan B pills, one Levonelle pill, 40 Ovrette pills, etc.) at once, as soon as possible after having unprotected intercourse (up to 5 days, or 120 hrs).