Plan B, an emergency contraceptive containing a high dose of the progestin levonorgestrel, is effective in preventing unplanned pregnancy is taken within 72 hours of unprotected sex. While generally well tolerated, Plan B can cause the following side effects:

  • Nausea (13-23% incidence)
  • Abdominal pain (13-18% incidence)
  • Headache (9-11% incidence)
  • Dizziness (9-10% incidence)
  • Menstrual pattern changes (10-12% incidence)


The side effect of 'menstrual changes' encompasses a variety of possibilities including:

  • Heavier than usual bleeding
  • Lighter than usual bleeding
  • Delayed menses


When To Expect Your Period After Taking Plan B

In most cases, you can expect to get your period around the same time you usually get it. In one clinical trial, most women (~87%) had their period at the expected time or within 7 days. On the other hand, around 13% of women had a delay of more than 7 days beyond the expected date of menses. In addition, a small percentage of women experienced amenorrhea (absence of menses).


Per the manufacturer of Plan B, if it has been more than 7 days from your expected menses, it is important to consider the possibility of pregnancy.  You should make an appointment with your doctor to be tested. A 7 day or greater delay doesn't necessary mean you are pregnant as the medication may simply have caused you to miss it. Nevertheless, it is important to be tested.


In terms of effectiveness, you can be pretty confident you were well protected from unplanned pregnancy. Perfect use of oral hormonal contraceptives has a effectiveness rate of over 97%. The use of Plan B within 72 hours of unprotected sex reduces the risk of pregnancy to about 1%. As you used both methods as required, pregnancy would be considered rate.