How Effective Is Emergency Contraception and What Methods Are Available?

Posted October 13, 2015 by Stacy Bolzenius

How Effective is Emergency Contraception?

Emergency contraception is used to prevent pregnancy after a patient has had unprotected or inadequately protected sex. There are two forms of emergency contraception available — emergency contraceptive pills and the copper intrauterine device (IUD). The pills can be either progestin-only, a combination of progestin and estrogen, or ulipristal. Each of these methods has been shown to be effective at preventing pregnancy if taken within five days of unprotected sex, but oftentimes women do not know they are available to them or misunderstand their use and safety.

To help reduce the number of unplanned pregnancies, it is important for OBGYNs to know the common brands of emergency contraception, as well as their safety and effectiveness, so they can share that information with their patients.

Emergency Contraceptive Pills

The most commonly used emergency contraceptive pill is the progestin-only pill, which contains 1.5 mg of levonorgestrel. The pill is available as either a single dose containing the full 1.5 mg or two doses of 0.75 mg taken 12 to 24 hours apart. The pill should be taken as soon as possible after the unprotected sex occurred although it is labeled for use up to three days after unprotected sex.

When taken in higher-than-usual amounts, the combined estrogen-progestin pill can be used as a form of emergency contraception. This form is taken in two doses, with the number of pills needed for emergency contraception varying for each brand. Again, combination pills should be taken as soon as possible but can be taken up five days, after unprotected sex.

Lastly, the ulipristal pill contains 30 mg of ulipristal acetate. Like the combination pills, ulipristal can be taken up to five days after unprotected sex with no decrease in effectiveness. This pill works as a progesterone receptor modulator, or antiprogestin, and is available by prescription only.

Intrauterine Devices

The IUD is a small, T-shaped device placed into the uterus by a doctor within five days after having unprotected sex. Patients can have the IUD removed after their next period, or can choose to have it left in place for up to 10 years to use as their regular birth control method. Although IUDs have been shown to be highly effective at preventing unplanned pregnancies if placed within five days, the Food and Drug Administration has not labeled it for use as an emergency contraception.

The Most Commonly Used Emergency Contraception is Progestin-Only Pills

Common Brands

Plan B One-Step, a progestin-only pill, is perhaps the most common form of emergency contraceptive used and is available over-the-counter at local pharmacies. As of 2013, the pill is available without age restrictions. Previously the pill was only available without a prescription to women age 17 and older, with those younger than 17 required to have a prescription.  As many women are unaware that the law has changed, it is important to make sure your patients understand that this is a readily available form of emergency contraceptive. Generic forms of Plan B include Next Choice One Dose, My Way and Take Action.

Both ulipristal and combination pills are available only by prescription, including Ella, an FDA approved form of ulipristal pill.

Effectiveness of Emergency Contraception

Studies have shown that progestin-only pills are about 75 percent effective in preventing pregnancy, with their effectiveness decreasing over time. The pills are most effective when taken within three days of unprotected sex, and moderately effective when taken within five days.

Two studies have looked at the effectiveness of progestin-only versus combination pills. Although the first study did not show a statistical difference in pregnancy rates, a second, larger trial reported that progestin-only pills prevented 85 percent of pregnancies while the combination pills prevented only 57 percent. Because it is more effective and associated with less nausea and vomiting than combination pills, progestin-only methods of emergency contraceptives are preferred.

Ulipristal pills have been shown to be more effective than progestin-only forms in multiple studies. In one trial, women using ulipristal pills had a pregnancy rate of 1.4 percent, compared to those taking the progestin-only pill who had a pregnancy rate of 2.2 percent.

The most effective form of emergency contraceptive, however, is the IUD, which has shown to be about 99 percent effective in preventing pregnancy. In a study of more than 1,800 women, there were no pregnancies within the first month after placing an IUD. Over the course of 42 studies spanning 35 years, pregnancy rates among women using IUDs as emergency contraception were between 0 and 2 percent.

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