From the Guidelines
Plan B (levonorgestrel) for emergency contraception should be taken as a single 1.5 mg tablet as soon as possible after unprotected sex, ideally within 72 hours but it can be effective up to 5 days afterward. The recommended dosage of levonorgestrel is a single 1.5-mg dose, which is available either as 2 pills (0.75 mg each) or as 1 pill (Plan B One-Step) 1. This dosage is preferred due to its superior adverse effect profile and effectiveness, which is up to 85% 1.
Key Points to Consider
- The sooner Plan B is taken, the more effective it is at preventing pregnancy.
- No prescription is needed for those of any age in the United States.
- Plan B works primarily by preventing or delaying ovulation, and may also prevent fertilization or implantation of a fertilized egg.
- Side effects may include nausea, abdominal pain, fatigue, headache, and menstrual changes, but these typically resolve quickly.
- Plan B is not effective if you're already pregnant and won't harm an existing pregnancy.
- It's less effective for women weighing over 165 pounds or with a BMI over 25, in which case ulipristal acetate may be a more effective option 1.
- After taking Plan B, use a backup contraception method until your next period, which may come earlier or later than expected.
- If you vomit within 2 hours of taking the pill, contact a healthcare provider as you may need another dose.
- If you don't get your period within 3 weeks or experience severe abdominal pain, seek medical attention.
Alternative Options
- Ulipristal acetate in a single dose (30 mg) is another option for emergency contraception, which may be more effective for women weighing over 165 pounds 1.
- Combined estrogen and progestin in a two-dose regimen is also available, but has a less favorable adverse effect profile compared to levonorgestrel 1.
From the Research
Dose and Administration of Plan B for Emergency Contraception
- The dose of Plan B, which contains levonorgestrel, is 1.5 mg, and it is effective up to 5 days after unprotected sexual intercourse 2.
- Plan B is available over-the-counter for women of all ages in the United States 3, 4.
- The mechanism of action of oral emergency contraception, including Plan B, is delay of ovulation, and it is ineffective postovulation 4.
- Women who weigh more than 75 kg or have a body mass index greater than 25 kg/m(2) may have a higher risk of unintended pregnancy when using oral levonorgestrel emergency contraception, and ulipristal acetate or copper intrauterine devices are preferable in this setting 4.
- Plan B should be taken as soon as possible after unprotected sexual intercourse, and it is recommended that women contact their health care providers after taking emergency contraceptive pills to discuss possible copper intrauterine device placement and other follow-up 5.
Efficacy and Comparison to Other Emergency Contraception Methods
- The copper intrauterine device has the highest efficacy for emergency contraception, followed by ulipristal acetate, levonorgestrel-containing emergency contraceptive pills, and the Yuzpe method 5.
- Ulipristal acetate tends to be more efficacious in pregnancy prevention than is levonorgestrel, especially when taken later than 72 hours postcoitus 4.
- The efficacy of emergency contraception decreases with time, and it is most effective when used within 72 hours of unprotected sexual intercourse 6, 3.
Special Considerations
- Women who are victims of sexual assault should be offered emergency contraception as soon as possible, and it is recommended that they be treated within 120 hours of the assault 6, 3.
- Women who are breast-feeding can use emergency contraception, but they should be counseled about the potential effects on milk production and infant exposure to the medication 4.
- Health care providers should be prepared to counsel women about emergency contraception options, provide emergency contraception appropriately, and refer for emergency contraception in a timely manner if needed 4.