Levonorgestrel vs Ulipristal Acetate: Understanding Your Options
Quick Answer
Levonorgestrel and ulipristal acetate are the two active ingredients used in emergency contraception pills. Levonorgestrel (found in Postinor, Plan B) is effective up to 72 hours and available OTC. Ulipristal acetate (found in Mifestad, Ella) maintains high effectiveness up to 120 hours, making it the better choice when more time has passed.
What Are These Ingredients?
These are the two main active ingredients in emergency contraception pills worldwide:
Levonorgestrel is a synthetic progestin used in many contraceptives since the 1960s. It's well-studied and widely available.
Ulipristal Acetate is a selective progesterone receptor modulator (SPRM) that was specifically developed for emergency contraception in the 2000s.
How They Work Differently
Both prevent pregnancy by affecting ovulation, but in different ways:
Levonorgestrel:
- Delays or prevents the LH surge that triggers ovulation
- Most effective before the LH surge begins
- Less effective once the surge has started
Ulipristal Acetate:
- Blocks progesterone receptors
- Can delay ovulation even after LH surge has begun
- Maintains effectiveness longer in the cycle
Effectiveness Comparison
Here's how effectiveness changes over time:
| Hours After Sex | Levonorgestrel | Ulipristal Acetate |
|---|---|---|
| 0-24 hours | 95% | 98% |
| 24-48 hours | 85% | 97% |
| 48-72 hours | 58% | 95% |
| 72-96 hours | Not recommended | 90% |
| 96-120 hours | Not effective | 85% |
When to Choose Each
Your timing and situation determine the best choice:
Within 24 hours: Either works well, levonorgestrel is more affordable
24-72 hours: Ulipristal acetate has significantly higher effectiveness
72-120 hours: Only ulipristal acetate is effective
On hormonal BC: Levonorgestrel won't interfere with your regular BC
Breastfeeding: Levonorgestrel is considered compatible
Find the right emergency contraception for your situation.
View OptionsFrequently Asked Questions
Yes, both are FDA-approved and considered safe for most people. Side effects are typically mild and temporary. Neither has long-term health effects.
No. Taking both together may actually reduce effectiveness. Choose one based on your timing and situation.
Levonorgestrel products are typically available over-the-counter. Ulipristal acetate usually requires a prescription or telemedicine consultation.
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