Ralph asked
My girlfriend and I had sex towards the end of her period and took plan b 4 hours later, could she be pregnant still?
Answer
Plan B (levonorgestrel) is a progestin containing emergency contraceptive used to prevent an unintended pregnancy after unprotected sex or in situations where the contraceptive method used fails (e.g. a broken condom).
Plan B is most effective when used within 72 hours of unprotected sex. In your case, taking Plan B 4 hours after intercourse is within the time frame in which Plan B is thought to be most effective.
How Does Plan B Work
Plan B (levonorgestrel) is thought to work via multiple mechanisms to prevent pregnancy but works mainly by inhibiting of ovulation (egg release). It may also delay embryo transport and make it more difficult for a fertilized egg to implant into the uterus by altering the endometrium.
Studies show that Plan B is fairly effective in preventing pregnancy after unprotected sex. Per the prescribing information for Plan B:
"The expected pregnancy rate of 8% (with no contraceptive use) was reduced to approximately 1% with Plan B One-Step."
There is some controversy in regard to whether or not Plan B is effective at all after ovulation, but Plan B is nevertheless indicated for use at any time during the menstrual cycle.
It is important to be aware that Plan B use may cause spotting, bleeding or missed menses during the cycle Plan B was taken. If menses is late or doesn't occur, it would be prudent to take a pregnancy test or make a doctors appointment to rule out the possibility of pregnancy.
Summary
- Plan B is most effective when used within 72 hours of unprotected sex.
