708 North Main Street, Suite 200, Blacksburg, VA 24060

1016 Fairfax St., Radford, VA 24141

Blacksburg: (540) 552-5556 Radford: (540) 838-2138

Ask a VWC Nurse: How Does the Morning After Pill Work?

morning after pill

Ask a VWC Nurse: Answers to Your Commonly Asked Questions

ask a nurse Once a month, we feature answers to commonly asked questions that our Valley Women’s Clinic medical staff receives. Our nurses provide answers to these questions here on the blog.

Q. How Does the Morning After Pill Work?

A. The morning after pill acts as an emergency contraceptive principally by preventing ovulation or fertilization. In addition, it may inhibit implantation. It is not effective once the process of implantation has begun.

Often known as “Plan B,” the morning after pill is a large dose of oral contraceptive containing the hormone progesterone. This hormone suppresses ovulation, thickens cervical mucus, and causes some changes in the uterine lining that can prevent the implantation of a developing embryo. The effectiveness of the morning after pill depends on the time in a woman’s cycle when the pill is taken.

When a couple has intercourse, the man’s sperm is ejaculated into the woman’s vagina. The sperm swim through vaginal and cervical mucus to get into the uterus to reach the woman’s egg (if it is present) in order to fertilize the egg. If the woman’s egg has not yet been released from her ovary, there will not be a conception leading to a pregnancy.

When a woman takes the morning after pill within 24-72 hours of intercourse, her ovulation will be delayed (if it has not already occurred for that month), preventing an egg from being released into her fallopian tube and uterus. In this scenario, a possible pregnancy is prevented.

If the woman’s egg has already been released and is still viable (within 12- 24 hours after its release), then a single sperm (viable up to 5 days after intercourse) could fertilize the egg, which would rapidly develop into an embryo. The morning after pill thickens cervical mucus, which reduces the probability of a sperm reaching the egg to cause fertilization, and therefore prevents a possible pregnancy.

If fertilization occurs, the embryo moves into the uterus from the place it was fertilized (probably the fallopian tube). The embryo seeks a place to implant into the wall of the uterine cavity. The progesterone hormone changes the uterine cavity wall’s receptivity and can interfere with implantation, preventing the developing embryo from getting the nutrition it needs to survive. So this causes the embryo to die, and the woman eventually gets her period. However, her period may be delayed or she may skip that month due to the effects of the progesterone hormone on her hormonal cycle.

Some Things About Emergency Contraception to Consider:

  • Emergency contraception is not effective if you are already pregnant.
  • The morning after pill does not protect against HIV infection (AIDS) and other sexually transmitted diseases.
  • According to Plan B’s manufacturer, Plan B is not as effective as regular contraception and is not recommended for routine use as a contraceptive.
  • Research shows that Plan B starts to lose its effectiveness in women heavier than 165 pounds and is not recommend for anyone over this weight.
  • The most common side effects of Plan B are nausea, abdominal pain, fatigue, headache and vomiting. Menstrual patterns are often irregular after taking Plan B.
  • If you experience severe lower abdominal pain after taking the morning after pill, seek immediate medical attention as you may have an ectopic pregnancy.
  • The morning-after pill is not the same as mifepristone (Mifeprex), also known as RU-486 or the abortion pill, according to the Mayo Clinic. That drug terminates an established pregnancy — one in which the fertilized egg has attached to the uterine wall and has already begun to develop.

Valley Women’s Clinic does not provide or refer for emergency contraception, but our medical staff can provide you with accurate medical information about it so that you can make an informed decision.

Keep in mind that emergency contraception is not effective if you’re already pregnant. So before you decide about using some form of emergency contraception, you may need to determine whether or not you’re already pregnant. Request an appointment with us at our Blacksburg or Radford clinic for a free pregnancy test. We also offer free STI testing for chlamydia and gonorrhea.

Do you have a question for one of our VWC nurses? Fill out the form below to anonymously ask your question and it could be featured on one of our future Ask a VWC Nurse blog posts!

Ask a Valley Women's Clinic Nurse



Older blog posts >