How Long Does the Morning After Pill Stay in Your System?

The active ingredient in most morning-after pills, levonorgestrel, has a half-life that averages about 24 hours, meaning roughly half the drug is cleared from your blood every day. Within two to three days, the vast majority of it is gone, and detectable traces typically disappear within about five days. But “how long it stays in your system” and “how long its effects last” are different questions, and the distinction matters more than many people realize.

How Quickly Levonorgestrel Leaves Your Blood

Levonorgestrel is the hormone in Plan B and its generic equivalents. In a pharmacokinetic study of women who took the standard 0.75 mg dose, the drug’s half-life ranged from about 16 to 32 hours, with a mean around 24 hours. The mean residence time in the body was roughly 28 hours.¹ Today’s single-dose Plan B contains 1.5 mg of levonorgestrel (double what was used in that study), so blood levels start higher, but the clearance rate is governed by the same metabolic pathways. As a rough guide, most of the drug is out of your plasma in two to three days, and functionally undetectable within four to five.

That timeline is for blood levels specifically. Your liver breaks levonorgestrel down through an enzyme system called CYP3A4, and the metabolites are excreted in urine and stool over a slightly longer period. But in terms of hormonal activity, the drug stops doing anything meaningful well before every last molecule has left your body.

Ulipristal Acetate Is a Different Drug With a Longer Timeline

If your morning-after pill was ella (ulipristal acetate, or UPA), the timeline is longer. UPA has a half-life of roughly 32 hours, and its active metabolite sticks around even longer. Where levonorgestrel is essentially a synthetic progestin that floods your system with a hormone signal, UPA works differently: it’s a progesterone-receptor modulator that blocks progesterone’s action at the receptor level.² That blocking effect can persist for several days after peak blood levels have passed, which is one reason ella can be taken up to five days after unprotected sex while levonorgestrel is best taken within three.

A study that doubled the dose of UPA to 60 mg found that blood concentrations roughly doubled as expected, but a standard 30 mg dose was still sufficient to delay ovulation regardless of body weight or BMI.³ So while more drug in your system means more drug to clear, the standard dose works without adjustment for most people.

What the Pill Does While It’s There

Both types of morning-after pill work primarily by delaying or preventing ovulation. When levonorgestrel is taken before the hormonal surge that triggers egg release, it can push ovulation back significantly. In one study, women who took 1.5 mg of levonorgestrel before their expected ovulation saw their cycles lengthen from an average of about 26 days to 39 days, because the drug delayed the hormonal surge that releases the egg.⁴ If you’ve already ovulated, the pill is much less effective. This is the central limitation that people often misunderstand: the morning-after pill doesn’t hang around creating a multi-day shield. It delivers a one-time hormonal intervention, and if the timing doesn’t catch your ovulation window, it has little to work with.

UPA has a slight advantage here because it can block ovulation even after the hormonal surge has begun, as long as the process hasn’t progressed too far. In animal models, UPA was a potent ovulation blocker when given within a critical window after the luteinizing hormone surge, but its effectiveness dropped sharply once the underlying signaling had already played out.² In both cases, the pill works during a specific window and then its contraceptive effect is done, even though traces of the drug remain in your body.

What You’ll Notice After Taking It

Even though levonorgestrel clears your blood within a few days, its effects on your menstrual cycle can be noticeable for weeks. A study of 232 women who took levonorgestrel EC found that about 15% experienced unexpected bleeding between periods, and many had measurable changes in cycle length, period duration, and flow appearance compared to their baseline. These changes depended on where in the cycle the pill was taken: women who took it well before expected ovulation tended to see different disruptions than those who took it around or after ovulation. The reassuring finding was that the majority of these changes disappeared by the following cycle.⁵

So if your period comes early, late, heavier, lighter, or with some spotting in between, that’s the drug’s downstream hormonal effect playing out. It doesn’t mean the drug is still active in your system. The hormonal disruption it caused days earlier is just taking time to resolve. If your period is more than a week late, a pregnancy test is a reasonable step, because at that point the delay is outside the range that EC alone explains.

Drugs That Clear It Faster Than Expected

Both levonorgestrel and ulipristal acetate are broken down by the same liver enzyme, CYP3A4. Anything that revs up that enzyme will push the morning-after pill out of your system faster, potentially before it’s had time to work. This isn’t a theoretical concern. A review of drug interaction studies found that known CYP3A4 inducers caused significant drops in levonorgestrel exposure, and estimated that CYP3A4 accounts for roughly 86% of UPA’s clearance, making UPA even more vulnerable to these interactions.⁶

What kinds of medications cause this? The most well-studied example is rifampin, a tuberculosis drug. Modeling work showed that co-administration with rifampin cut levonorgestrel exposure roughly in half.⁷ Other CYP3A4 inducers include certain anti-seizure medications (like carbamazepine and phenytoin), the HIV drug efavirenz, and the herbal supplement St. John’s wort. On the flip side, strong CYP3A4 inhibitors like itraconazole (an antifungal) can increase levonorgestrel levels by about 50%.⁷

If you’re taking any of these medications, the morning-after pill may not reach high enough levels to work. This is one situation where a copper IUD is a much better emergency contraception option, because its effectiveness doesn’t depend on drug metabolism at all.

Breastfeeding and How the Drug Passes Into Milk

For nursing mothers, “how long does it stay in my system” often really means “how long will it be in my breast milk?” A pharmacokinetic study of lactating women who took the 1.5 mg dose of levonorgestrel found that the drug appeared in breast milk within a couple of hours, peaking around two to four hours after the dose. Milk concentrations tracked the pattern of blood levels but were consistently lower, with an average milk-to-plasma ratio of 0.28. The estimated infant exposure was about 1.6 micrograms on the day the mother took the pill, dropping to 0.3 micrograms the next day and 0.2 micrograms on the third day.⁸

Those amounts are very small. For context, infants whose mothers take daily levonorgestrel-only contraceptive pills are exposed to similar or greater cumulative amounts on an ongoing basis. Most medical guidelines do not recommend interrupting breastfeeding after taking levonorgestrel EC. If you wanted to minimize even that small exposure, pumping and discarding milk for the first six to eight hours after the dose would cover the peak concentration period. By day three, the drug is present only in trace amounts.

What Happens If You Vomit After Taking It

Because the pill needs to be absorbed through your gut, vomiting soon after taking it can mean you didn’t get enough of the drug into your bloodstream. The clinical recommendation is straightforward: if you vomit within three hours of taking either levonorgestrel or ulipristal acetate, you should take another dose.⁹ This matters because the drug is absorbed relatively quickly. Levonorgestrel reaches peak blood levels within about one to two hours after swallowing the tablet. So if you manage to keep it down for three hours, absorption is essentially complete and vomiting afterward won’t change your drug levels.

This is worth knowing ahead of time, because nausea is one of the more common side effects of emergency contraception. If you have a history of medication-related nausea, an anti-nausea medication taken about an hour before the morning-after pill can help. The three-hour redosing guideline applies to UPA as well.⁹

Restarting Regular Birth Control After ella

This is where the “how long does it stay in your system” question gets practically important for people who use hormonal birth control. If you took ella (UPA) and then immediately restart your combined oral contraceptive pills, the two drugs can work against each other. UPA blocks progesterone receptors, while your regular pill delivers progestin that activates those same receptors. One study that explored this timing found that women who immediately restarted their combined pills after taking UPA had no ovulations with pregnancy risk during the five days following UPA. But among women who delayed restarting their pills, about 17% ovulated with a theoretical risk of pregnancy before the end of that cycle.¹⁰

This creates an awkward dilemma. You want to restart your pills to get back on track with regular contraception, but you also don’t want the progestin in your pills to counteract the UPA that’s still circulating. Current guidance generally recommends waiting five days after taking ella before restarting hormonal contraception, and using condoms during that window. The five-day delay aligns roughly with UPA’s functional duration in the body, even though trace amounts may linger a bit longer. If you took levonorgestrel (Plan B) instead of ella, this concern doesn’t apply in the same way, because levonorgestrel and the progestin in your regular pills work through the same mechanism rather than opposing each other.

Oral Route Versus Other Routes

An interesting wrinkle in how long the drug stays in your system is that the route of administration matters. A study comparing vaginal and oral administration of levonorgestrel found that vaginal delivery produced substantially lower peak blood levels (about 5.4 versus 15.2 nanograms per milliliter) and took much longer to reach those peaks. Overall bioavailability was only about 62% of what oral dosing achieved.¹¹ This is why the morning-after pill is taken orally: you need a rapid, reliable spike in blood levels to disrupt the ovulation process in time. A slower, flatter absorption curve means less drug where it needs to be, during the narrow window when it matters.

When a Non-Pill Option Avoids the Question Entirely

If the concern about how long a morning-after pill stays in your system is driven by wanting reliability, the copper IUD sidesteps the whole issue. It contains no hormones, doesn’t depend on your metabolism or liver enzymes, and works by creating an environment that’s inhospitable to fertilization. A systematic review and meta-analysis found that the copper IUD was substantially more effective than levonorgestrel-based methods for emergency contraception.¹² A clinical review ranked it as the most effective emergency contraceptive available, ahead of both ulipristal acetate and levonorgestrel pills.¹³

Beyond the immediate emergency use, the copper IUD provides ongoing contraception for over a decade. An observational study found that women who chose the copper IUD for emergency contraception were about half as likely to become pregnant over the following year compared to those who chose oral levonorgestrel.¹⁴ The catch is access: getting a copper IUD placed within five days requires a clinic visit and a provider who can insert it on short notice, which is a real barrier for many people. But if you can get one, it’s the most effective option and it leaves nothing to metabolize.

1
PubMed. Pharmacokinetics of levonorgestrel 0.75 mg tablets
2
PubMed Central. Ulipristal blocks ovulation by inhibiting progesterone receptor-dependent pathways intrinsic to the ovary
3
BMJ Sexual & Reproductive Health. Double dosing ulipristal acetate emergency contraception for individuals with obesity: a randomised crossover trial
4
PubMed. Effect of single administration of levonorgestrel on the menstrual cycle
5
PubMed Central. Menstrual bleeding patterns following levonorgestrel emergency contraception
6
PubMed. Drug interactions between emergency contraceptive drugs and cytochrome inducers: literature review and quantitative prediction
7
PubMed Central. Quantitative Assessment of Levonorgestrel Binding Partner Interplay and Drug-Drug Interactions Using Physiologically Based Pharmacokinetic Modeling
8
Human Reproduction. Levonorgestrel pharmacokinetics in plasma and milk of lactating women who take 1.5 mg for emergency contraception
9
Pediatrics. Emergency Contraception
10
ScienceDirect (Elsevier / Contraception). The effects on ovarian activity of delaying versus immediately restarting combined oral contraception after missing three pills and taking ulipristal acetate 30 mg
11
Contraception / ScienceDirect. Bioavailability of the Yuzpe and levonorgestrel regimens of emergency contraception: vaginal vs. oral administration
12
PubMed. Comparison of levonorgestrel in different forms and copper intrauterine devices for emergency contraception: A systematic review and meta-analysis
13
PubMed Central. Emergency contraception review: evidence-based recommendations for clinicians
14
PubMed Central. Emergency contraception with a copper IUD or oral levonorgestrel: an observational study of 1-year pregnancy rates