How effective would the Plan B pills be if I took them about 100 hours (4-5 days) after unprotected s*x?

Question

please let me know your source! Thank you!

Answer 1

Not very....It's called the morning after pill for that reason.  I think the most effective is the sooner the better.  After 72 hours, you're too late and shouldn't take it.  Talk to your pharmacist.

Answer 2

The effectiveness of emergency contraception is presented differently from the effectiveness of ongoing methods of birth control: it is expressed as a percentage reduction in pregnancy rate for a single use of EC. Different ECP regimens have different effectiveness levels, and even for a single regimen different studies may find varying rates of effectiveness. Using an example of "75% effective", an article in American Family Physician explains the effectiveness calculation thus:

... these numbers do not translate into a pregnancy rate of 25 percent. Rather, they mean that if 1,000 women have unprotected intercourse in the middle two weeks of their menstrual cycles, approximately 80 will become pregnant. Use of emergency contraceptive pills would reduce this number by 75 percent, to 20 women.[13]

The progestin-only regimen (using levonorgestrel) is reported by the U.S. FDA to have an 89% effectiveness. As of 2006, the labeling on the U.S. brand Plan B explained this effectiveness rate by stating, "Seven out of every eight women who would have gotten pregnant will not become pregnant."[14]

In 1999, a meta-analysis of eight studies of the combined (Yuzpe) regimen concluded that the best point estimate of effectiveness was 74%.[15] A 2003 analysis of two of the largest combined (Yuzpe) regimen studies, using a different calculation method, found effectiveness estimates of 47% and 53%.[16]

For both the progestin-only and Yuzpe regimens, the effectiveness of emergency contraception is highest when taken within 12 hours of intercourse and declines over time.[3][17][18] While most studies of emergency contraception have only enrolled women within 72 hours of unprotected intercourse, a 2002 study by the World Health Organization (WHO) suggested that reasonable effectiveness may continue for up to 120 hours (5 days) after intercourse.[19]

For 10 mg of mifepristone taken up to 120 hours (5 days) after intercourse, the combined estimate from three trials was an effectiveness of 83%.[20] A review found that many trials found a regimen of 25-50 mg of mifepristone to have higher effectiveness. However, when reviewers looked at only high-quality trials, the difference in effectiveness was not statistically significant