Why is a female of reproductive age with no known underlying medical conditions experiencing premenstrual syndrome (PMS) symptoms but no menstrual bleeding, after having a normal period, followed by intercourse and taking the I-pill (levonorgestrel) within 24 hours?

Delayed Menstruation After Emergency Contraception (I-Pill)

The most likely explanation is that levonorgestrel emergency contraception (I-pill) has disrupted your normal menstrual cycle, causing a delay in your period despite experiencing PMS symptoms—this is a common and expected side effect that occurs in many women after taking emergency contraception. 1

Why This Happens

• Levonorgestrel works by delaying or stopping ovulation, which directly disrupts the normal hormonal cascade that triggers menstruation 1
• When taken within 24 hours as you did, the medication is highly effective at preventing ovulation, but this mechanism inherently alters your menstrual timing 1
• Your period may arrive at the expected time, within one week of the expected time, or be delayed beyond one week—all of these patterns are documented normal responses to emergency contraception 1

What Your PMS Symptoms Mean

• PMS symptoms without bleeding indicate hormonal fluctuations are occurring, but the normal progression to menstruation has been interrupted by the levonorgestrel 2
• The presence of premenstrual symptoms does NOT guarantee that bleeding will follow on schedule after emergency contraception use 1

Critical Next Steps

If your period is delayed more than one week beyond the expected date, you must take a pregnancy test, as this delay could indicate pregnancy rather than just medication effect 1

When to Take Action:

• Immediate pregnancy testing is required if your period is more than 7 days late from when you expected it 1
• Seek immediate medical attention if you develop severe abdominal pain, as this could indicate ectopic pregnancy 1

Expected Timeline and Patterns

• Most women experience their next period within one week (early or late) of their expected date after taking levonorgestrel 1
• Your period may be heavier, lighter, earlier, or later than usual—all are normal variations after emergency contraception 1
• The disruption is typically limited to one cycle, with subsequent cycles returning to your baseline pattern 1

Important Caveats

• Emergency contraception is approximately 87.5% effective (prevents 7 out of 8 expected pregnancies), meaning pregnancy remains possible even with correct use 1
• The sooner emergency contraception is taken after intercourse, the more effective it is—you optimized this by taking it within 24 hours 1
• If you vomited within 2 hours of taking the I-pill, the dose may have been lost and pregnancy risk increases 1

When to Suspect Other Causes

While medication effect is most likely, consider pregnancy testing now (rather than waiting) if:

• You had any episodes of vomiting within 2 hours of taking the I-pill 1
• You are taking medications that reduce levonorgestrel effectiveness (efavirenz for HIV, rifampin for tuberculosis, or seizure medications) 1
• Your period becomes more than one week late 1

The bottom line: A delayed period with PMS symptoms after taking emergency contraception within 24 hours is most commonly due to the medication's effect on your ovulation and menstrual timing, but pregnancy must be ruled out with a test if your period does not arrive within one week of the expected date. 1