Can a Person Take a Morning After Pill After Ovulation?
Yes, a person can and should still take emergency contraception even after ovulation has occurred, though effectiveness varies significantly by medication type and timing relative to ovulation. The copper IUD remains highly effective post-ovulation, while oral emergency contraceptives have reduced but not absent efficacy.
Understanding Mechanism and Timing
The effectiveness of emergency contraception after ovulation depends critically on which method is used:
Oral Emergency Contraceptives Post-Ovulation
Levonorgestrel (Plan B) has minimal to no effectiveness if ovulation has already occurred 1. The FDA label for ulipristal acetate explicitly states that levonorgestrel "is no longer effective" when administered after the LH surge has begun 1. The primary mechanism is delaying or inhibiting ovulation—once the egg is released, this mechanism cannot work 1.
Ulipristal acetate (ella) has limited effectiveness immediately before ovulation but becomes ineffective once ovulation occurs 1. Pharmacodynamic studies showed that ulipristal postponed follicular rupture in 79% of subjects when taken immediately before ovulation (when LH was rising), but "treatment was not effective in postponing follicular rupture when administered on the day of LH peak" 1. This represents the actual moment of ovulation.
The Copper IUD: The Post-Ovulation Solution
The copper IUD is the only emergency contraception method that remains highly effective after ovulation has occurred 2. CDC guidelines specifically state that "when the day of ovulation can be estimated, the Cu-IUD can be inserted beyond 5 days after sexual intercourse, as long as insertion does not occur >5 days after ovulation" 2. The copper IUD works through a different mechanism—creating a toxic environment for sperm and preventing implantation—with a failure rate of <1% 3.
Clinical Decision Algorithm
If Ovulation Status is Unknown (Most Common Scenario)
- Within 72 hours of intercourse: Use levonorgestrel 1.5 mg single dose for normal-weight women 3, 4
- Within 72 hours but weight >165 lbs: Prefer ulipristal acetate 30 mg over levonorgestrel 3
- 72-120 hours post-intercourse: Use ulipristal acetate 30 mg, which maintains 65% lower pregnancy risk compared to levonorgestrel in this window 3, 5, 6
- Any timepoint within 5 days: Copper IUD insertion provides maximum efficacy regardless of timing or weight 3
If Ovulation Has Definitively Occurred
Strongly recommend copper IUD insertion as the only reliably effective option 2, 3. The IUD can be inserted up to 5 days after ovulation occurred 2.
Oral emergency contraceptives (both levonorgestrel and ulipristal acetate) should still be offered if IUD insertion is not feasible, acceptable, or immediately available, though patients must understand the significantly reduced effectiveness 1. The potential endometrial effects mentioned in the FDA label for ulipristal acetate ("alterations to the endometrium that may affect implantation may also contribute to efficacy") provide theoretical but unproven benefit post-ovulation 1.
Critical Caveats
Timing of ovulation is extremely difficult to determine clinically 2. Even women with regular 26-32 day cycles show "great variability" in the timing of the 6-day fertile window 2. Unless a woman was actively tracking ovulation with LH testing or ultrasound, assume ovulation status is unknown and proceed with the algorithm above.
Do not withhold emergency contraception based on suspected post-ovulation timing 2. CDC guidelines recommend ECPs "should be taken as soon as possible within 5 days of unprotected sexual intercourse" without qualification about ovulation status 2.
After taking ulipristal acetate, barrier contraception is required for 14 days or until next menses if starting hormonal contraception 3, 1. Progestin-containing contraceptives may impair ulipristal's ability to delay ovulation if taken too soon 1.