EllaOne (ulipristal acetate) has a half-life of approximately 32 hours, meaning it takes roughly 5 to 7 days for the drug to be fully cleared from your body. Most of the active effects wear off sooner than that, but trace amounts remain detectable in your system for close to a week. If you’re asking because you’re planning to start hormonal contraception, breastfeed, or take another medication, the timeline matters in different ways depending on the situation.
How Your Body Processes EllaOne
After you swallow the tablet, your body breaks it down primarily through a liver enzyme called CYP3A4. The drug reaches peak blood levels within about an hour, then gradually declines. With a half-life of around 32 hours, the concentration drops by half roughly every day and a half. After five half-lives, a drug is considered essentially eliminated, which puts full clearance at about 6 to 7 days for most people.
Side effects like nausea, headache, or abdominal pain typically start within a few hours and fade within one to three days. If side effects persist beyond a few days, that’s worth bringing up with a pharmacist or doctor.
Factors That Speed Up or Slow Down Clearance
Certain medications and supplements change how quickly your body processes ellaOne, sometimes dramatically. Drugs that speed up that liver enzyme (CYP3A4 inducers) can slash the drug’s blood levels by as much as 90%. The herbal supplement St. John’s Wort falls into this category, along with some epilepsy medications like carbamazepine, phenytoin, and topiramate. If you’ve been taking any of these, ellaOne may clear your system faster, but it also may not work as well.
On the other side, certain antifungal medications can slow clearance significantly. In one study, a strong CYP3A4 inhibitor increased ellaOne’s exposure in the bloodstream by nearly sixfold. That means the drug lingers longer and at higher concentrations, which could also extend how long you experience side effects.
What This Means for Starting Hormonal Contraception
This is one of the most practical reasons people search for clearance times. EllaOne works by blocking progesterone receptors, and hormonal contraceptives (the pill, patch, ring) rely on progesterone to function. Taking both at the same time can reduce the effectiveness of either one. The standard recommendation is to wait at least 5 days after taking ellaOne before starting or restarting hormonal birth control. Use a barrier method like condoms during that waiting period and for the first days of your new contraceptive cycle.
Breastfeeding After EllaOne
Small amounts of ulipristal acetate do pass into breast milk. Older guidance suggested pumping and discarding milk for 24 hours after taking the tablet, but current FDA-approved labeling no longer requires a breastfeeding pause. The drug is not considered a reason to stop breastfeeding. If you’re concerned, talk to your prescriber about the most up-to-date advice for your situation.
How Body Weight Affects the Drug
Body weight doesn’t change how long ellaOne stays in your system in a clinically meaningful way, but it can influence how well the drug works. Analysis of clinical data found that for women with a BMI of 30 or higher, the failure rate for ellaOne was 2.6%, compared to 0.9% for women in the normal weight range when taken within 24 hours. One model estimated that ellaOne may lose effectiveness at a BMI of 35 or above. That said, ellaOne still outperformed the other common morning-after pill (levonorgestrel) at every weight category studied.
How Long EllaOne Actually Works
EllaOne prevents pregnancy by delaying or suppressing ovulation. It remains effective as emergency contraception for up to 120 hours (5 days) after unprotected sex, which is longer than levonorgestrel-based options. In clinical trials, the pregnancy rate was 0.9% when taken within 24 hours and 1.3% when taken within 120 hours. Among women who took it between 72 and 120 hours after sex, zero pregnancies occurred in the ellaOne group, while three occurred in the levonorgestrel group.
The drug’s contraceptive action, delaying the release of an egg, is largely complete within the first few days. After that, the remaining drug in your system isn’t contributing much to pregnancy prevention; your body is simply finishing the job of metabolizing and excreting what’s left.
Effects on Your Next Period
Because ellaOne suppresses progesterone activity and delays ovulation, it commonly shifts the timing of your next period. Your cycle may come a few days early or a few days late. This is a direct consequence of the hormonal disruption and not a sign that the drug is still active in your body. If your period is more than 7 days late, a pregnancy test is a reasonable next step.