From the Guidelines
The recommended dosage of Plan B (levonorgestrel) is a single 1.5-mg dose, which can be taken as one pill or two pills (0.75 mg each) as soon as possible after unprotected sex or contraceptive failure. This emergency contraceptive should be taken within 72 hours (3 days) of unprotected intercourse, though it is most effective when taken within the first 24 hours 1. No second dose is needed. Plan B works primarily by preventing or delaying ovulation, and may also prevent fertilization or implantation of a fertilized egg. It will not terminate an existing pregnancy. Some key points to consider when taking Plan B include:
- Side effects may include nausea, abdominal pain, fatigue, headache, and menstrual changes, with your next period potentially coming earlier or later than expected.
- If vomiting occurs within 2 hours of taking the pill, contact a healthcare provider as you may need another dose.
- Plan B is less effective in women weighing more than 165 pounds (75 kg), and alternative emergency contraception might be recommended in these cases 1. It's essential to note that while Plan B is effective, its efficacy decreases with time, and it's crucial to take it as soon as possible after unprotected sex. Additionally, ulipristal acetate may be a more effective option for women who weigh more than 165 pounds, as it has been shown to have increased effectiveness over oral levonorgestrel at the end of the 5-day window of use and in heavier women 1.
From the Research
Plan B Dosage
The recommended dosage of Plan B, also known as levonorgestrel, is as follows:
- A single 1.5 mg pill (Plan B One-Step) 2, 3, 4
- Two 0.75 mg pills taken 12 hours apart (Next Choice) 2, 3, 5
- Alternatively, two 0.75 mg pills can be taken 24 hours apart 5
Efficacy and Safety
The efficacy of levonorgestrel in preventing pregnancy is moderate, with a success rate of around 80% 6. It is most effective when taken as soon as possible after unprotected intercourse, but it can be taken up to 5 days after 2, 6, 4. The safety profile of levonorgestrel is similar to or better than other oral emergency contraceptives, with common side effects including nausea, vomiting, headache, and breast tenderness 6.
Administration
Levonorgestrel can be administered in different dosing strategies, including a single 1.5 mg dose or two 0.75 mg doses taken 12 or 24 hours apart 3, 5. The American College of Obstetricians and Gynecologists recommends a single dose of levonorgestrel 1.5 mg as one option for emergency contraception 3.