After a single dose, mifepristone takes roughly 6 to 7 days to clear from your body, with most of the drug and its breakdown products eliminated through stool. Blood levels become undetectable by about 11 days. The timeline depends on your dose, metabolism, and whether you’re taking other medications that affect how your liver processes the drug.
Half-Life and What It Means for You
Mifepristone has an elimination half-life of roughly 20 to 30 hours after a single dose. That means every 20 to 30 hours, the amount of active drug in your blood drops by half. After one day, about half the drug remains. After two days, about a quarter. After four to five half-lives (roughly 4 to 6 days), the remaining amount is small enough to be functionally negligible.
This timeline changes significantly with repeated dosing. For people taking mifepristone daily to manage conditions like Cushing syndrome, the half-life extends to around 85 hours. That’s because the drug accumulates in the body over time, and the liver’s processing capacity becomes more saturated. In that scenario, full clearance takes considerably longer.
How the Body Breaks It Down
Your liver does most of the work. A specific enzyme called CYP3A4 is the primary workhorse, breaking mifepristone into three main metabolites through two chemical processes: stripping off small chemical groups and adding oxygen to part of the molecule’s structure. All three of these metabolites are biologically active, meaning they can still interact with your body’s receptors even as the original drug is being dismantled.
This matters because even after the parent drug starts disappearing from your blood, its metabolites linger. In forensic blood samples taken a day after a dose, researchers found that one metabolite was actually present at higher concentrations than mifepristone itself (639 ng/mL vs. 557 ng/mL). When blood is drawn well after a dose, metabolites may be the only detectable evidence that the drug was taken.
How the Drug Leaves Your Body
Mifepristone exits primarily through your digestive system. After a 600 mg dose, about 83% is recovered in stool and 9% in urine over the course of 11 days. By that 11-day mark, blood levels are undetectable. The bulk of elimination happens in the first 6 to 7 days, with the remainder tapering off gradually.
The heavy reliance on fecal excretion reflects how the liver processes the drug and sends its byproducts into bile, which then moves through the intestines. This is a different route than many common medications, which tend to be eliminated mostly through urine.
What Can Slow Clearance Down
Because CYP3A4 handles most of the metabolism, anything that interferes with this enzyme can change how long mifepristone stays in your system. Substances that inhibit CYP3A4, including grapefruit juice, certain antifungal medications, and some antibiotics, can slow metabolism by 70 to 80%, keeping blood levels elevated for longer. Conversely, strong CYP3A4 inducers (like some anti-seizure medications or St. John’s wort) can speed up clearance.
Mifepristone also binds very tightly to proteins in your blood: about 98% of the drug is attached to blood proteins at any given time. Only the unbound fraction is active and available for your liver to process. This high protein binding is one reason the drug lingers. It creates a reservoir effect where bound drug slowly releases into circulation as the free drug gets metabolized.
Breastfeeding Considerations
For nursing parents, the dose matters. After a single 200 mg dose (the standard for medical abortion protocols in many countries), mifepristone was undetectable in breast milk at all time points measured in a small study of two women. After a 600 mg dose, the picture is different: breast milk levels averaged 172 mcg/L on day one, dropped to 66 mcg/L by day two, and continued declining to about 25 mcg/L by day five. Levels peaked in milk samples collected 6 to 9 hours after the dose and dropped substantially by 9 to 15 hours.
Even at the higher dose, researchers estimated a fully breastfed infant would receive only about 0.5% of the mother’s weight-adjusted dose. The general guidance from lactation research is that breastfeeding does not need to be interrupted after a single dose used for medical abortion, though the 200 mg dose is preferable for nursing mothers. For long-term mifepristone use, the manufacturer recommends pumping and discarding milk during treatment and for 18 to 21 days after the last dose.
Detection in Lab Tests
Mifepristone does not show up on standard drug screens. It requires specialized toxicology testing that specifically looks for the drug and its metabolites. In the blood, the parent drug and its breakdown products can be identified at least one day after a dose with certainty. The metabolites, particularly the one formed by removing a single chemical group, may remain detectable longer than mifepristone itself because of their higher concentrations and comparable or longer half-lives.
Clinical pharmacokinetic studies use a 14-day washout period between doses to ensure complete elimination, which gives a practical upper bound. If researchers need two full weeks to be confident the drug is entirely gone for study purposes, that’s a reasonable ceiling for how long trace amounts could theoretically persist in your system.