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The morning-after pill leaves your body within a few days, though its effect on your cycle can last longer than the drug itself does. Levonorgestrel, sold as Plan B and several generics, clears fastest, with most of the dose gone inside about two days. Ulipristal acetate, sold as ella, has a terminal half-life of roughly 32 hours, so traces remain measurably longer.
Neither figure tells you whether it worked, which is the question most people are really asking. Urban Recovery, an NY rehabilitation center in Brooklyn, publishes this because medication questions reach our intake line constantly. What follows separates how long the medication lingers from how long it acts, and flags the situations where a pharmacist is worth a phone call.
How Long Each Type Stays Active
Both types work by stopping or delaying ovulation, which means both depend entirely on where you are in your cycle when you take them. Neither interrupts an established pregnancy.
Levonorgestrel is absorbed quickly, peaks within a couple of hours and is broken down in the liver over the following day or two. It is licensed for use within 72 hours of unprotected sex and loses effectiveness noticeably as that window closes, so the difference between hour six and hour sixty is substantial. Ulipristal holds its effect further into the cycle and is licensed up to 120 hours, which is the main practical reason a clinician might choose it.
The lingering drug is not what protects you. Once ovulation has been delayed, the delay stands whether or not the medication is still detectable, and your cycle re-establishes itself over the following weeks.
What Changes How Fast You Clear It
Clearance varies between people, though not by enough to change the dosing advice. The factors that matter most are the ones that affect whether the dose reaches your bloodstream at all.
• Vomiting within about three hours of taking it, which may mean the dose never absorbed.
• Liver function, since both medications are metabolized there, in the same way that governs how long doxycycline stays in your system.
• Body weight, which some research suggests reduces levonorgestrel effectiveness at higher weights, though the evidence is mixed and guidance differs by country.
• Enzyme-inducing medicines, which speed up breakdown and lower the concentration in your blood.
• Where you are in your cycle, which does not affect clearance but determines whether the medication can do anything at all.
A pharmacist can work through these with you in a few minutes and without an appointment. That conversation is worth having before you take it rather than after.
What To Do If You Vomit Soon After Taking It
Vomiting within roughly three hours of the dose means a repeat dose is usually recommended, because the tablet may not have absorbed. After three hours, absorption is generally complete and a second dose is unnecessary.
Nausea is a common side effect in its own right, which creates an awkward loop. If you have vomited on emergency contraception before, tell the pharmacist, because they can advise on timing with food or suggest the copper IUD, which sidesteps the issue entirely and is the most effective emergency option available.
Medicines And Supplements That Can Weaken It
Several drugs induce the liver enzymes that clear these medications, which lowers the concentration in your blood and can reduce effectiveness. The list includes certain anticonvulsants such as phenytoin and carbamazepine, some antibiotics used for tuberculosis such as rifampicin, certain HIV medications, and St John's Wort, which people often forget to mention because it is sold as a supplement.
Ulipristal also interacts with hormonal contraception in a way that catches people out. It can be blunted by recent progestogen, and starting or restarting hormonal birth control immediately afterward can reduce its effect. Ask specifically about restarting timing rather than assuming.
Tell whoever dispenses the medication about everything you take, including supplements and anything prescribed by a different clinic. The interaction risk here is a genuine one, unlike several of the claims that circulate online.
What The Research Does Not Support
Claims that emergency contraception shows up on blood, urine or hair tests are wrong, and they appear on a surprising number of health pages. There is no routine test that screens for levonorgestrel or ulipristal, and neither appears on standard drug panels used by employers, courts or treatment programs. Nothing about taking emergency contraception will register on a test you are asked to give.
Alcohol is the other common worry. There is no good evidence that drinking changes how either medication works. The practical risk runs the other way: heavy drinking is a well-documented reason people miss the timing window altogether, fail to notice a condom failure, or vomit inside the absorption window. The pharmacology is fine. The circumstances are the problem.
If drinking has repeatedly put you in situations you would not otherwise have been in, that is worth taking seriously on its own terms, and our drug detoxification services exist for the point at which it stops being occasional.
Side Effects And Your Next Period
Most side effects appear within the first 24 hours and settle within a few days. Nausea, fatigue, headache, dizziness and breast tenderness are the common ones, and they reflect a single high hormone dose rather than any lasting change.
Your next period is the part people underestimate. It may arrive several days early or several days late, and it may be heavier or lighter than usual. That variation is expected and does not indicate failure. A period more than a week late, or unusually light bleeding when you expected a normal period, is a reason to take a pregnancy test. Severe abdominal pain in the weeks afterward warrants same-day medical attention rather than waiting.
Frequently Asked Questions
How soon should I take it?
As soon as you reasonably can. Levonorgestrel is most effective in the first 24 hours and declines across the 72-hour window, while ulipristal holds effectiveness further out to 120 hours. Neither works once ovulation has already happened, which is why hours genuinely matter rather than days.
Will it stop a pregnancy that has already started?
No. Emergency contraception prevents or delays ovulation, and it has no effect on an established pregnancy. If you already know you are pregnant, these medications are not the relevant option and a clinician should advise you directly.
Can I take it more than once in a cycle?
It is safe to take more than once, though repeat use makes cycle disruption more likely and it is far less effective than ongoing contraception. Frequent need is a signal to talk to a clinician about a method that does not depend on catching a window afterward.
Does it affect future fertility?
No evidence suggests any effect on long-term fertility. Ovulation resumes in the following cycle, and you can become pregnant soon afterward, which is why continuing contraception matters in the days after taking it.
Questions about how a medication interacts with drinking or drug use are worth asking a clinician rather than a search engine. Our licensed team in Brooklyn, New York answers that kind of question every day, and you can reach the intake line at (646) 347-1892 without an appointment or a referral.
Urban Recovery, Inpatient Detox and Rehabilitation, Brooklyn
Address: 411 Van Brunt Street, Brooklyn, NY 11231
Intake: (646) 347-1892
Email: admissions@urbanrecovery.com
