Aftera’s active ingredient, levonorgestrel, has an elimination half-life of about 27.5 hours, meaning your body clears half the dose roughly every day. After five to six half-lives, a drug is considered effectively gone from your bloodstream, putting Aftera’s total clearance time at approximately 5 to 7 days. That said, the hormonal effects it triggers can linger a bit longer than the drug itself.
How Your Body Processes Aftera
After you swallow the 1.5 mg tablet, levonorgestrel is absorbed into your bloodstream and metabolized by your liver. About 45% of the drug and its byproducts leave through urine, and about 32% exit through feces. With each passing day, roughly half of the remaining levonorgestrel is broken down and eliminated. By day five or six, levels in your blood are negligible.
This timeline assumes normal liver function. Certain medications speed up the liver enzymes responsible for breaking down levonorgestrel, which can clear the drug faster and reduce its effectiveness. These include some medications used to treat epilepsy (such as carbamazepine and phenytoin), tuberculosis drugs like rifampicin, certain HIV medications, and the herbal supplement St. John’s wort. One HIV medication, efavirenz, reduces levonorgestrel blood levels by around 50%. These enzyme-boosting effects can persist for up to four weeks after you stop taking the interacting medication, so even recently discontinued drugs can matter.
How Long the Effects Last
Even though the drug itself clears in under a week, the hormonal disruption it causes can affect your body for longer. Aftera works primarily by delaying or preventing ovulation, and that shift in your hormonal cycle doesn’t snap back the moment levonorgestrel leaves your blood.
The most noticeable lasting effect is on your period. Your next cycle may arrive up to a week later than expected. If it’s more than a week late, a pregnancy test is a reasonable next step. Some people also experience spotting in the days after taking the pill, which can continue for up to a week. Other common side effects like nausea, headache, and fatigue tend to resolve more quickly, typically within a day or two as your body adjusts.
Body Weight and How Quickly It Works
Your weight can influence how effectively Aftera works before it clears your system. Research published in the journal Contraception found that pregnancy rates rose significantly at higher body weights. Among women weighing 65 to 75 kg (roughly 143 to 165 pounds), the estimated pregnancy rate was 1.4%. That jumped to about 6% for women weighing 75 to 85 kg (165 to 187 pounds). The steepest drop in effectiveness occurred between 70 and 80 kg, with pregnancy risk climbing sharply around that range.
BMI showed a similar pattern, with efficacy declining around a BMI of 26. This doesn’t mean Aftera won’t work at higher weights, but the hormonal dose may be diluted across more body tissue, reducing peak blood levels before the drug is cleared. If you weigh more than about 165 pounds, a copper IUD or a different emergency contraceptive (the one containing ulipristal acetate) may be more reliable options to discuss with a provider.
The Effectiveness Window
Aftera is most effective when taken as soon as possible after unprotected sex. It’s approved for use within 72 hours (three days), with overall effectiveness in that window ranging from 81% to 90% at preventing pregnancy. The sooner you take it, the closer you are to the higher end of that range. Taking it within the first 24 hours gives you the best odds.
There is some evidence that levonorgestrel-based emergency contraception still offers reduced protection between 73 and 120 hours (three to five days), though it becomes less reliable the longer you wait. After five days, the drug is not considered effective for pregnancy prevention.
Pregnancy Testing After Aftera
Levonorgestrel does not interfere with pregnancy test results. It’s a synthetic form of progesterone, not the hormone (hCG) that pregnancy tests detect, so it won’t cause a false positive. However, timing matters. If you take a test too soon after the encounter, there may not be enough hCG in your system to register even if conception occurred. Waiting at least two weeks after the sexual encounter gives you the most accurate result. If your period is more than a week late, that’s a good signal to test.
Returning to Regular Contraception
Because Aftera clears your system within about a week, it offers no ongoing pregnancy protection. You can become pregnant from sex that happens even a day or two after taking it. If you’re using hormonal birth control like the pill, patch, or ring, you can restart or continue it right away. Aftera won’t cancel out your regular contraception, but it also won’t extend it. Use a backup method like condoms for at least seven days after restarting hormonal birth control, since your regular method needs time to become fully effective again.