Emergency contraception with levonorgestrel (1.5 mg single dose) is MOST effective when taken within:

• A 12 hours of unprotected intercourse
• B 72 hours, with decreasing effectiveness over time ✓
• C 120 hours (5 days), with equal effectiveness throughout
• D 24 hours only; ineffective thereafter

Explanation

Levonorgestrel emergency contraception (Plan B / ECP) is most effective when taken as soon as possible after unprotected intercourse, with efficacy declining over time: ~95% effective within 24 hours, ~85% at 25–48 hours, ~58% at 49–72 hours. The 72-hour window is the approved timeframe. Beyond 72 hours, a copper-IUCD inserted within 5 days is the most effective emergency contraceptive option (>99%). Ulipristal acetate (ella) can be used up to 120 hours with more uniform efficacy. Levonorgestrel acts primarily by delaying/inhibiting ovulation; it does NOT prevent implantation of a fertilised egg.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.