Do Not Take Plan B Followed by Ella
You should not take Ella (ulipristal acetate) after taking Plan B (levonorgestrel) because these medications can interfere with each other's effectiveness, and the FDA specifically warns against using additional levonorgestrel emergency contraceptive pills within 5 days of taking Ella. 1
Why This Combination Is Problematic
The interaction works in both directions and creates a pharmacological conflict:
Levonorgestrel can reduce Ella's effectiveness: The FDA drug label for Ella explicitly states that "additional levonorgestrel emergency contraceptive pills should not be used within 5 days of Ella intake" 1
The mechanism of action differs: Ella (ulipristal acetate) is a selective progesterone receptor modulator that works by blocking progesterone receptors, while Plan B (levonorgestrel) is a progestin that activates these same receptors 2, 3. Taking levonorgestrel first and then ulipristal creates a competitive antagonism where the medications work against each other.
Ella remains effective for longer: Ulipristal acetate can prevent pregnancy when administered up to 120 hours (5 days) after unprotected intercourse and is actually more effective than levonorgestrel, particularly after 72 hours 4, 5. Taking Plan B first wastes this superior efficacy window.
What You Should Do Instead
If you've already taken Plan B and are concerned about its effectiveness:
Do not add Ella on top of Plan B - this will not improve your protection and may reduce overall effectiveness 1
Wait and monitor for pregnancy: Take a pregnancy test if your period is more than 1 week late 1
Start or resume barrier contraception immediately: Use condoms with spermicide for any subsequent intercourse until your next menstrual period 1
Consider starting regular hormonal contraception: After using Plan B, you can start any regular contraceptive method immediately without waiting 6
If You Haven't Taken Anything Yet
Choose Ella over Plan B if you are beyond 72 hours from unprotected intercourse:
Ella is significantly more effective than Plan B between 72-120 hours, with 65% lower pregnancy risk in the first 24 hours and 42% lower risk up to 72 hours 2, 4
The CDC specifically notes that ulipristal acetate may be more effective than levonorgestrel formulations after the first 72 hours and for women who are overweight or obese 7
Critical Timing Considerations
For Plan B specifically:
- Most effective within 72 hours but can be used up to 120 hours 6
- Reduces pregnancy risk by at least 75% when taken within 72 hours 6
- Effectiveness decreases significantly as time passes 6
For Ella specifically:
- Approved for use up to 120 hours (5 days) after unprotected intercourse 1, 4
- Maintains effectiveness even in the advanced follicular phase when LH levels are rising, a time when levonorgestrel no longer works 3
Important Warnings After Taking Either Medication
After Plan B: You can start any regular contraceptive method immediately 6
After Ella: You must wait 5 days before starting or resuming hormonal contraception (pills, patch, ring), and use barrier methods during this waiting period 1, 5
The bottom line: Taking both medications sequentially is counterproductive and potentially harmful to efficacy. If you've already taken Plan B, do not add Ella. If you haven't taken anything yet and are within 120 hours, choose the single most appropriate emergency contraceptive based on timing and body weight considerations.