Emergency contraception (EC) is also called the morning-after pill (MAP) and by its
medical name levonorgestrel. EC is available in the United States under the brand
name Plan B. It is an oral medication that can be taken after unprotected sex or
contraceptive failure in order to prevent a pregnancy from occurring. Plan B consists
of 2 pills containing the same hormone (0.75 mg of levonorgestrel). The first pill
is taken by mouth as soon as possible after intercourse (up to 72 hours after).
The second pill should be taken by mouth 12 hours following the first pill. EC
is available over the counter if you are at least 18 years old, but if you are under
18 years old, you’ll need a prescription from your doctor.
How does EC work?
To understand how emergency contraception works and when it should be taken, you
should understand a bit about the fertility cycle, because there is actually only
a small window of time when it will prevent a pregnancy. You do not need to know
this information to take EC since it can be taken at any time in your cycle, but
it is helpful information for you to have. Please talk to your doctor or pharmacist
for further help with determining if you need to take EC.
Sperm can live up to 5 days in fertile cervical fluid (the fluid that can be found
inside your vagina). Women ovulate once per cycle, and once they have ovulated,
there is only a 24-hour window that the egg can be fertilized by sperm before it
dies. This means that there are a total of 6 days per cycle that a woman can get
Prior to ovulation, an egg grows within your ovary. Once the egg is mature enough,
an increase in a hormone called LH will begin (known as the LH surge). Within 24-48
hours, LH will cause the egg to pop out of the ovary and begin its trip into the
uterus. On this trip, it might be fertilized if there are sperm present. If an egg
is fertilized, it will implant within the uterus approximately 7-10 days after ovulation.,
and approximately 4 days after that, you would miss your period and discover you
Emergency contraception acts primarily by stopping ovulation from occurring. It
does this by interfering with LH.
Taking EC prior to the surge in LH (which occurs 24 to 48 hours before ovulation)
will delay ovulation by approximately 5 days - long enough to be sure that any sperm
cells have died off.
Taking EC during or after your LH surge will likely have no effect on preventing
a pregnancy because the wheels are already set in motion for you to ovulate.
Taking EC after ovulation will likely have no effect on preventing a pregnancy since
ovulation has already occurred.
Frequently Asked Questions
Does EC cause an abortion?Emergency contraception does not cause an abortion. (It
is not the same as the abortion pill, RU-486.) For an abortion to take place, the
embryo must first be implanted into the uterine lining. If this has already occurred,
EC will have no effect on the developing embryo or fetus. If you take Plan B accidentally
while you are pregnant or if it does not work and you become pregnant, it is not
likely to cause any harm to you or the baby.
Can EC stop the implantation of a developing embryo?Some studies have raised a concern
that emergency contraception might stop an embryo from implanting into the wall of
the uterus by either (1) reducing the quality of the uterine lining or (2) by interfering
with the corpus luteal cyst, causing it to produce decreased progesterone and therefore
impacting the uterine lining. Most studies disprove these actions, so this action
should not be relied on to prevent a pregnancy. However, these studies cannot be
absolutely verified, and we may never know the truth. If this were an action of EC,
an embryo that might normally implant into the uterine lining would not have a chance
to do so and would instead be lost during your period. After learning this information,
it will be up to you to decide whether or not this possibility is important enough
to avoid use of EC. Some women feel strongly that any medication that might impact
a developing human is not okay to take. These women would want to avoid using EC.
Other women, after learning the risks and possibilities, might decide that it is
okay to take. Use your own belief system to decide for yourself.
Can EC have an impact on sperm cells or cervical fluid? Likewise, there have been
studies that suggest emergency contraception affects your cervical fluid, thereby
making it difficult for sperm to swim in. However, this has also not been proven,
and it should not be relied on to prevent a pregnancy.
How much does EC cost? You can expect to pay between $20 and $45 for Plan B.
What are the side effects of EC? Menstrual changes (25%), nausea (23%), abdominal
pain (18%), fatigue (17%), headache (17%), dizziness (11%), breast tenderness (11%),
vomiting (6%), and diarrhea (5%). If you vomit within 1 hour after taking either
pill, please call your doctor for further instructions. You may need to take an
Is there anyone who should not take EC? If you have unusual vaginal bleeding or
an allergy to birth control pills, tell your doctor before taking Plan B. You should
not take Plan B if you are allergic to birth control pills. Small amounts of Plan
B do pass into breast milk, and while there have been no reports of harm to nursing
infants, it's always a good idea to notify your doctor before taking Plan B if you
Can I still get pregnant after using EC?Since ovulation could occur approximately
5 days after beginning treatment with emergency contraception, it is important to
avoid intercourse or use contraception following the use of EC. Your period could
be delayed by 5-7 days as well, but if your period has not started after that point,
a pregnancy test should be taken.
Does EC protect against STDs? Emergency contraception does not protect you from sexually
transmitted disease. Only contraceptive methods that block the exchange of bodily
fluids will protect you from an STD (for instance, the male condom).
Can I use EC repeatedly?Emergency contraception should not be used as your main
method of birth control. While it is okay to take on more than one occasion, EC
should not be used monthly or more often than that. It is less effective than a
consistent form of birth control, and although there are no safety precautions given
by the FDA regarding repeat use, there have been no long-term studies that reveal
the bodily response to this high-dose of hormones.
How effective is EC?Emergency contraception is anywhere from 59% to 94% effective,
depending on the study used. Commonly, the effectiveness is stated as 89%, meaning
that instead of the usual 8-10 women who would get pregnant from sex that occurred
near ovulation, with EC only 1 or 2 of them would go on to become pregnant.
When should I start EC?Emergency contraception needs to be started within 72 hours
(3 days) of having sex. However, EC is more effective the sooner it is taken after
intercourse, and ideally, it should be started within the first 24 hours after intercourse.
Are there age restrictions or limitations on EC?Anyone who is sexually active can
take emergency contraception no matter the age. You do not need your parent's permission
to get a prescription for EC, although your doctor may have a policy of notifying
parents about a teenager's medical care. You can call anonymously and ask what your
physician's policy is on this issue. Anyone younger than 18 will need a prescription
to get EC.
Can I use regular birth control pills for EC?In some instances, you may be able
to use regular birth control pills as emergency contraception. This usually consists
of taking multiple pills at a time out of your birth control pack. Each dose has
a different requirement to be effective. Since EC is available and is relatively
easy to purchase and use, it is recommended that you use that method, especially
since taking multiple birth control pills can cause nausea and vomiting, which would
make them ineffective. However, you can call your doctor or pharmacist to find out
the dosage that needs to be taken of your particular brand of birth control pill.
Can I use an IUD for EC?It is also possible to have an intrauterine device (IUD)
inserted into your uterus by your physician to be used as emergency contraception.
Please note that this will not prevent ovulation, but it will prevent an already
developing embryo from implanting itself within your uterine lining. Since this
is more costly and difficult to receive, most women will choose to ask their physicians
for a prescription for emergency contraception.
Are there medications that interfere with EC?The effectiveness of Plan B is reduced
by phenytoin, carbamazepine, barbiturates, and rifampin. If you are on these medications,
please let your doctor know before taking Plan B.