- Prevents 75% of expected pregnancies
- Requires 2 doses, 12 hours apart
- Each dose contains at least 100 mcg of ethinyl estradiol
and 500 mcg of levonorgestrel
- May cause nausea and vomiting
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The most commonly used method for emergency contraception is
a special regimen of combined oral contraceptives. This regimen
has been studied extensively and shown to be safe and effective.
When used correctly, emergency contraceptive pills prevent about
75 percent of expected pregnancies.
Two doses of pills should be taken: the first within 72 hours
after unprotected intercourse and the second 12 hours later.
Each of the two doses of pills should contain at least 100 micrograms
of ethinyl estradiol and 500 micrograms of levonorgestrel (LNG),
which can be obtained either by taking four "low-dose"
pills or two "high-dose" pills in each dose.
The mechanism of action is not well understood and may be related
to the time it is used in a woman's cycle. It is believed that
the main effect is the inhibition or delay of ovulation. It
may also interfere with fertilization and/or implantation. Once
implantation has occurred, emergency contraceptive pills are
not effective.
Counseling young women about the possible side effects of emergency
contraceptive pills is important. The main side effects are
nausea, which about one-half of women experience, and vomiting,
experienced by up to one-fifth of women after the first or second
dose.
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Learner Note: The common low-dose
pills contain 30 micrograms of ethinyl estradiol and 150
micrograms of levonorgestrel. The common high-dose pills
contain 50 micrograms of ethinyl estradiol and 250 micrograms
of levonorgestrel.
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