How Effective Is Plan B Emergency Contraceptive In Preventing Pregnancy?

Posted on Mon, 16 Nov 2015

Medically reviewed by Ask A Doctor - 24x7 Medical Review Team

Tue, 17 Nov 2015 Answered on

Thu, 3 Dec 2015 Last reviewed on

Question : Plan B question.

Is plan B still effective once ovulation has occurred or started?

If someone had unprotected sex and may have been ovulating, took plan B 1 step 16 hours later.

Answered by Dr. Jacqueline Brown (5 hours later)

Brief Answer:
Plan B is designed to be effective during ovulation

Detailed Answer:
Hello, and I hope I can help you today.

Plan B and other emergency contraceptives, if taken within 72 hours of unprotected intercourse, are designed to work even if you have already ovulated.

Plan B can inhibit or delay ovulation if taken before it occurs, but it also causes decreased transport of the egg through the Fallopian tube and thickens cervical mucus which can interfere with sperm transport.
These other effects help protect against fertilization.

However, the morning-after pill is still only 90 percent effective in preventing pregnancy, which means 10 percent of women will conceive even if they used the medication correctly.

So, in summary, the medication is most likely to work, but if you miss your next period you should take a pregnancy test.

I hope I was able to answer your question and that my advice was helpful. If you need anything further, please do not hesitate to contact me again.

Best wishes, Dr. Brown

Above answer was peer-reviewed by : Dr. Raju A.T