When can Plan B (levonorgestrel) be given for pregnancy prevention?

When Can Plan B Be Given for Emergency Contraception

Plan B (levonorgestrel) emergency contraception should be taken as soon as possible within 5 days (120 hours) after unprotected sexual intercourse, with greater effectiveness the earlier it is taken. The optimal timing for Plan B administration is within 72 hours (3 days) of unprotected intercourse, but it can still be effective when taken up to 120 hours afterward. 1

Timing and Administration

• Plan B should be taken as soon as possible after unprotected intercourse to maximize effectiveness 1
• While the FDA-approved labeling indicates administration within 72 hours, research shows effectiveness when used within 120 hours (5 days) after unprotected intercourse 1, 2
• Treatment initiated within 72 hours reduces pregnancy risk by at least 75% 1
• Single-dose administration (Plan B One-Step 1.5 mg) is as effective as the original two-dose regimen (0.75 mg taken 12 hours apart) 2, 3
• If using the two-dose regimen, both doses can be taken at the same time without decreasing efficacy or increasing side effects 1

Effectiveness Considerations

• Effectiveness decreases as time passes after unprotected intercourse 1
• Pregnancy rates are low when Plan B is administered within 4 days but increase at 4-5 days after unprotected intercourse 1
• Plan B is more effective than the older Yuzpe regimen (combined estrogen-progestin) and has fewer side effects 4
• Plan B may be less effective in women with higher body weight, though it should still be offered 1

After Taking Plan B

• Any regular contraceptive method can be started immediately after using Plan B 1
• The woman should abstain from sexual intercourse or use barrier contraception for 7 days after starting regular contraception 1
• Advise the woman to have a pregnancy test if she does not have a withdrawal bleed within 3 weeks 1
• If vomiting occurs within 3 hours of taking Plan B, another dose should be taken as soon as possible 1

Advance Provision

• An advance supply of Plan B may be provided so it will be available when needed and can be taken as soon as possible after unprotected intercourse 1
• Studies show that advance provision increases use of emergency contraception but does not adversely affect regular contraceptive behavior 1, 5

Common Side Effects and Management

• Side effects include nausea, vomiting, headache, breast tenderness, and transient alteration of menstrual bleeding pattern 5
• Levonorgestrel causes less nausea and vomiting than combined estrogen-progestin emergency contraception pills 1
• Routine use of antiemetics before taking Plan B is not recommended, but pretreatment may be considered based on clinical judgment 1

Mechanism of Action

• When given before the preovulatory LH peak, Plan B primarily works by blocking or delaying ovulation 5
• It may also affect sperm migration in the female reproductive tract and have an effect on fertilization 5
• There is no evidence for an anti-implantation effect 5

Plan B should be recognized as a backup method that is not a substitute for the continued use of more effective regular contraceptive methods 5, 6.