How Long Does Plan B Stay in Your System?

The short answer

Plan B does not linger long. Its active ingredient, levonorgestrel, reaches its peak level in your blood within about one to two hours of swallowing it, and from there your body steadily breaks it down and clears it away. The amount of it in your system drops by roughly half every twenty-four to thirty-two hours, which is what its half-life means, so after a single day about half is gone, and after just a few more days only a small fraction remains.

Putting all of that together, a single dose is essentially fully cleared from your body within about five to seven days, with only negligible trace amounts possibly lingering a little longer than that. That brief stay matters for two very practical reasons: it is why the side effects pass within days, and it is why the pill cannot provide any ongoing contraception, since there is simply nothing left in your system to protect you a week later.

So the headline is a peak within hours, a half-life of roughly a day, and essentially full clearance within about a week. The rest of this guide breaks down that timeline, explains what can speed it up or slow it down, and answers the practical questions people have about drug tests and starting other contraception.

The clearance timeline

Because the drug halves at a steady rate, its level in your body follows a predictable downward curve. Here is roughly how much remains over the days after a single dose.

The figures shown above are illustrative estimates of how a drug with this particular half-life clears over time, not exact measurements for any one individual person. What they show is the shape of it: a fast rise to a peak within a couple of hours, a halving each day or so, and very little left by the end of a week. The first day or two does the heavy lifting, carrying the level from its peak down to around a quarter, after which the remaining fraction tapers off gradually. By day five most people have only a few percent left, and by day seven the amount is so small that it has no meaningful effect on the body at all. Your liver does the great majority of the breaking-down work, converting the drug into byproducts that then leave your body mainly through urine and, to a lesser extent, through stool.

Understanding half-life

The word half-life gets used a lot in these explanations, so it is worth a plain definition, because once it clicks, the whole clearance timeline makes sense.

What half-life means

A drug’s half-life is simply the time it takes for the amount in your body to drop by half. The single key thing to grasp here is that each half-life removes half of whatever amount is left at that moment, not half of the original dose each time. So after one half-life you are at about fifty percent, after two you are at about twenty-five percent, after three about twelve percent, and so on. The amount falls quite quickly at first and then more and more gently, tapering smoothly toward zero rather than dropping off a cliff all at once.

Why that gives about a week

In pharmacology, a drug is generally considered essentially cleared after roughly five half-lives, by which point only a few percent remains. For levonorgestrel, with a half-life of about twenty-four to thirty-two hours, five half-lives works out to roughly five to seven days. That is exactly where the common figure of about a week comes from in the first place. It is not that the drug suddenly disappears at the end of a week; it is simply that the steady, repeated halving has reduced it to a negligible amount by that point.

Understanding this also explains why the clearance figure is a range rather than a precise day. Because the halving rate varies a little between people, the point at which the remaining amount becomes negligible shifts slightly too, which is why five to seven days is the honest answer rather than a single fixed number.

Staying in your system vs working

This is the most important point to get straight, because the two ideas are easy to confuse, and confusing them leads to false reassurance.

Two different questions

How long Plan B stays in your system, around five to seven days, is a pharmacology question about clearance. How long Plan B works after sex, within seventy-two hours and sometimes up to one hundred and twenty, is a question about the window in which taking it can still help. The fact that traces of the drug remain in your body for several days does not mean it is actively protecting you for those days. It does its single job, nudging the timing of ovulation, around the time you take it, and then it simply clears.

No ongoing protection

The practical upshot is that Plan B offers no protection against sex that happens after you take it. If you have unprotected sex again a few days later, the leftover drug in your system will not prevent a pregnancy from that new encounter; you would need another dose or, better, an ongoing method. This is one of the central differences between emergency and regular contraception, which we explain in is Plan B the same as birth control.

Keeping these two timelines separate is what prevents a costly misunderstanding. A few days of clearance is not a few days of cover, and treating it as such could leave you unprotected when you thought you were not.

A helpful way to hold the distinction is to think of the dose as a one-time action rather than a shield. It acts on a single moment in your cycle, the approach of ovulation, and either succeeds in delaying it or does not. Once that moment has passed, the drug’s purpose is served, and whatever amount remains in your bloodstream over the following days is just on its way out, doing nothing to guard against any new exposure.

What affects how long it stays

The five-to-seven-day figure is an average, and a few factors can shift it somewhat in one direction or the other.

Your own metabolism

Levonorgestrel is broken down by liver enzymes, and how quickly those enzymes work varies from person to person, partly due to genetics. Studies note that clearance can differ several-fold between individuals, which is why the half-life is given as a range rather than a single number. Beyond genetics, your body weight, liver function, and overall general health can also play a part in the pace of clearance. For most people, though, these differences still land within roughly the same week-long clearance window. A faster metabolizer might be essentially clear in four to five days and a slower one in closer to seven, but the variation is measured in a day or two, not in weeks. So while your personal timing is not identical to anyone else’s, it is close enough that the general guidance holds for nearly everyone.

Medications that speed it up

Certain medications and supplements speed up the liver enzymes that clear levonorgestrel, which can both shorten how long it stays and, more importantly, reduce how well it works. These include the antibiotic rifampin, the herbal supplement St. John’s wort, and some seizure and HIV medications. We cover these interactions, and which everyday medicines do not affect Plan B, in Plan B with antibiotics and ibuprofen.

For everyday purposes, none of this changes the basic picture much. Barring a specific enzyme-inducing medication, you can expect a single dose to be essentially gone within about a week, give or take, regardless of small individual differences.

Does it show on a drug test?

A question that comes up surprisingly often is whether Plan B will show up on a drug test or cause you to fail one. The answer is no.

Standard drug tests, the kind typically used for employment, sports, or similar screening purposes, are designed to look for specific drugs of abuse, such as cannabis, opioids, amphetamines, and cocaine. Plan B is none of these. Its active ingredient is a hormone, levonorgestrel, which is not a controlled substance and is not something drug panels are designed to detect. So a recent dose of Plan B will simply not register on a standard drug screen and will not cause a positive result of any kind.

So you can set this particular worry aside entirely and with confidence. Emergency contraception is a hormone medication, not a drug of abuse in any sense, and it has no bearing whatsoever on the results of a standard drug test of any common kind.

Does taking it late or taking two pills change how long it stays?

A couple of specific scenarios come up often: taking the pill late in the window, and taking more than one tablet. Neither changes the basic clearance picture in the way people sometimes expect.

Taking it early or late in the window

The clearance clock starts when you swallow the pill, not relative to when the sex happened. So whether you take Plan B a few hours after sex or closer to the end of the window a couple of days later, it still clears over about five to seven days from the moment you take it. Taking it late in the window may well affect how well it works, since effectiveness depends heavily on timing relative to ovulation, but it does not make the drug stay in your body any longer than usual.

Two tablets or a repeat dose

Some older emergency contraception came as two smaller tablets taken twelve hours apart, while the modern version is a single combined dose. Either way, the total amount clears in roughly the same week-long window. And if you happen to take a separate dose later on, perhaps after vomiting soon after the first one or for an entirely new situation, each dose clears on its own independent timeline rather than stacking into one long, prolonged presence in your body.

The takeaway is that the roughly week-long clearance is remarkably consistent. What genuinely varies with timing and dosing is the effectiveness, not how long the drug remains in your system, which stays firmly anchored to that steady, predictable half-life.

Why side effects fade as it clears

The clearance timeline also explains one of the most reassuring facts about Plan B: its side effects are temporary, because they are tied to the drug being present.

Effects like nausea, tender breasts, fatigue, headache, and spotting come from the brief hormonal shift the dose creates. As the drug clears over the following days, that shift unwinds and the effects ease. Most resolve within a day or two, and once the hormone is essentially gone by about a week, your body returns to its normal baseline. There is no lasting residue causing ongoing symptoms, for the simple reason that there is no lasting residue at all once the drug has cleared.

So if you are currently feeling the effects of a dose, the clearance timeline is genuinely good news: as the drug leaves your body over the next several days, the symptoms reliably leave along with it. The one exception to the few-days rule is your period, which may be shifted for that cycle, but that is your cycle adjusting, not the drug hanging around. That distinction matters, because someone whose period is a week late might worry the drug is still affecting them, when in fact the medication left their system days earlier and what they are seeing is the downstream effect on the timing of a single cycle.

How long until you feel like yourself again

Often the real question behind how long Plan B stays in your system is a simpler one: how long until I feel back to normal? The reassuring answer is usually sooner than full clearance.

Feeling normal comes first

Most people feel like themselves again within just a day or two, as the peak level passes and the acute effects like nausea, dizziness, or fatigue settle down. You do not have to wait out the full week for the drug to be completely gone before you feel fine again, because the most noticeable effects ease well before the very last traces clear. There is no lingering grogginess, fog, or hangover effect from a single dose; once the early effects pass, you are generally right back to normal in your day-to-day life.

Your cycle is the last to resettle

The one part that can lag behind is your menstrual cycle. Even after the drug is fully cleared and you feel completely normal, your next period may still arrive shifted for that one cycle, before settling back to its usual pattern. That is simply your cycle adjusting to the brief timing nudge, not the drug hanging around in your body, and we explain it in full in can Plan B mess up your cycle.

So if you are simply waiting to feel like yourself, that usually happens quickly. The longer timelines, full clearance and a resettled cycle, run quietly in the background and do not require you to feel unwell the whole time. For most people, the experience is a day or two of mild effects, then back to normal.

Starting regular birth control

Because Plan B clears quickly and does not block other hormones, it does not stand in the way of starting or resuming a regular method. In fact, doing so is a good idea if you want ongoing protection.

You can start right away

After taking a dose of Plan B that contains levonorgestrel, you can start or restart a regular hormonal birth control method right away or the very next day. Keep in mind that the regular method itself takes about seven days to become reliable, so use a backup like condoms, or avoid unprotected sex, during that first week. The leftover Plan B in your system does not interfere in any way with your regular method getting properly established.

A note on ella

One important exception is the other emergency pill, ella, which is a different drug and does interact with starting hormonal birth control, requiring a short wait. That does not apply to Plan B, but it is worth knowing if you are choosing between them, which we compare in ella vs Plan B.

This is a practical silver lining of the quick clearance. Far from leaving you in limbo, a dose of Plan B clears out of the way fast enough that you can set up dependable protection almost immediately if you choose to.

Repeated use and breastfeeding

Two more practical questions tie back to how quickly the drug clears: what happens if you take it more than once, and whether it is compatible with breastfeeding.

On fertility more broadly, the quick clearance is part of why Plan B has no lasting effect on your ability to conceive. There are simply no irreversible effects on your fertility once the drug is out of your system, and your normal cycle resumes on its own, as we explain in can Plan B make you infertile.

These points all flow from the same fact at the heart of this guide: a single dose is a short-lived visitor in your body, not a lasting presence, which is what makes it both safe to repeat when needed and gentle enough to use while nursing.

Common myths about Plan B “lingering”

A few persistent myths suggest Plan B sticks around far longer or does far more than it actually does. The clearance facts put each of them to rest.

What ties all these myths together is a misunderstanding of how briefly the drug actually stays. Once you know it clears in about a week and acts only around the time you take it, none of the lingering claims hold up. It is a short-acting medication, not a long-term presence in your body.

These myths tend to spread because emergency contraception carries a lot of emotional weight, and worry naturally attaches itself to the idea that something powerful must be lingering or doing more than it appears. The reality is more mundane and more comforting. The dose is modest, its action is narrow, and its stay is brief. Knowing the simple pharmacology, rather than the rumor, is the surest antidote to the anxiety these myths create.

Cutting through these myths leaves a simple, accurate picture. Plan B comes, does one specific job, and goes, all within the space of a few days, which is exactly how a single emergency dose is meant to behave.

Frequently asked questions

Sources & references

This article is based on pharmacology references and reputable health publishers. Always confirm details with a current source or a clinician for your situation.