Is Plan B (levonorgestrel) still effective when taken up to 72 hours (3 days) after unprotected sexual intercourse?

Is Plan B Still Effective 3 Days After Intercourse?

Yes, Plan B (levonorgestrel) remains effective when taken up to 72 hours (3 days) after unprotected intercourse, though effectiveness decreases with time and you should take it as soon as possible. 1, 2

Timing and Effectiveness Window

• Plan B can be used within 72 hours (3 days) of unprotected intercourse, as confirmed by both FDA labeling and CDC guidelines 3, 2
• The medication can actually work up to 120 hours (5 days) after intercourse, though it is most effective in the first 72 hours 1
• Treatment initiated within 72 hours reduces pregnancy risk by at least 75%, with approximately 7 out of 8 women who would have become pregnant avoiding pregnancy 1, 2
• Effectiveness decreases as time passes after unprotected intercourse, with pregnancy rates remaining low when administered within 4 days but increasing at 4-5 days 1

Critical Timing Principle

• The sooner Plan B is taken after unprotected intercourse, the better it works - this is the single most important factor for maximizing effectiveness 1, 2
• Levonorgestrel is estimated to be up to 85% effective overall when used appropriately 3

Important Weight Considerations

• Plan B loses effectiveness in women weighing more than 165 pounds and may be ineffective in women weighing more than 176 pounds 3
• Despite reduced effectiveness at higher body weights, Plan B should still be offered, though ulipristal acetate may be a better alternative for heavier women 3, 1

Dosing Options

• The standard dose is a single 1.5 mg tablet taken once 3, 2
• If using the two-dose regimen (0.75 mg each), both doses can be taken simultaneously without decreasing efficacy or increasing side effects 1

After Taking Plan B

• If vomiting occurs within 2-3 hours of taking the medication, another dose should be taken as soon as possible 1, 2
• Any regular contraceptive method can be started immediately after using Plan B, but a barrier method should be used or abstinence maintained for 7 days 3, 1
• Expect your next period at the expected time or within one week - if your period is delayed beyond 1 week, take a pregnancy test 3, 2

Common Pitfalls to Avoid

• Do not delay taking Plan B while deciding - every hour counts for maximizing effectiveness 1, 2
• Do not assume Plan B won't work at 72 hours - it can still prevent pregnancy, just with reduced effectiveness 1
• Do not use Plan B as regular birth control - it is a backup method only and less effective than regular contraceptive methods 3, 2
• Do not forget that Plan B does not protect against HIV or other sexually transmitted infections - condoms should always be used for STI protection 3, 2

Drug Interactions

• Certain medications may reduce Plan B effectiveness, including efavirenz (HIV medication), rifampin (tuberculosis treatment), and seizure medications 3, 2
• If taking these medications, consult a healthcare provider who may prescribe ulipristal acetate or recommend copper IUD placement instead 3, 2