Aftera is highly effective at preventing pregnancy, but how well it works depends almost entirely on how quickly you take it. In clinical studies, levonorgestrel emergency contraceptive pills like Aftera reduced the risk of pregnancy by 87% to 90% when taken within 72 hours of unprotected sex, with a pregnancy rate of just 0.8% to 2.1% depending on timing.
How Timing Changes Effectiveness
Aftera contains 1.5 mg of levonorgestrel, the same active ingredient found in Plan B One-Step and other over-the-counter emergency contraceptives. The single most important factor in how well it works is the clock. Every hour that passes after unprotected sex reduces the pill’s ability to prevent pregnancy.
Within 72 hours (three days), studies show a pregnancy rate of about 0.8%, which translates to an 87% to 90% reduction in expected pregnancies. Between 72 and 120 hours (three to five days), the pregnancy rate rises to 1.8%, with effectiveness dropping to 72% to 87%. The pill can still be taken up to five days after sex, but its protective effect weakens considerably toward the end of that window. Taking it within the first 24 hours gives you the best odds.
How Aftera Prevents Pregnancy
Aftera works primarily by delaying or blocking ovulation. The levonorgestrel in the pill suppresses the hormonal surge your body needs to release an egg from the ovary. If ovulation hasn’t happened yet, the pill can prevent it, which means there’s no egg available to be fertilized. It also thickens cervical mucus, making it harder for sperm to reach an egg. This is why timing matters so much: if you’ve already ovulated, the pill has less to work with. It’s most effective during the pre-ovulation window of your cycle.
Weight Can Reduce Effectiveness
One of the less widely known limitations of Aftera is that body weight affects how well it works. Health Canada has stated that levonorgestrel may be less effective in women over 165 pounds and potentially ineffective in women over 176 pounds. A BMI of 30 or higher has been linked to increased pregnancy risk after using levonorgestrel-based emergency contraception.
That said, the evidence isn’t definitive. The European Medicines Agency reviewed the same data and concluded it was “too limited and not robust enough” to draw firm conclusions. Medical organizations in Canada have recommended that women with a higher BMI should not be discouraged from using levonorgestrel if it’s what’s available, since some protection is better than none. But if you weigh more than 165 pounds and have time to access alternatives, a prescription option or a copper IUD may offer better protection.
Aftera vs. Ella
Ella (ulipristal acetate) is a prescription-only emergency contraceptive that works through a different mechanism. When comparing the two within the full five-day window, Ella has a lower pregnancy rate: 1.3% compared to 2.2% for levonorgestrel products like Aftera. Ella was associated with roughly 41% fewer pregnancies than levonorgestrel in a meta-analysis of two large randomized trials.
Within the first 72 hours, though, the difference narrows significantly, and the two are associated with similar pregnancy rates. Ella’s advantage really shows up in the later part of the window, between days three and five. It also maintains its effectiveness better in women with a BMI of 25 or higher, which is why clinical guidelines recommend Ella as the first-choice hormonal option for women in that weight range who prefer emergency contraception in pill form.
The most effective emergency contraceptive overall is a copper IUD, which can be inserted up to five days after unprotected sex and reduces pregnancy risk by more than 99%, regardless of body weight.
Common Side Effects
Most people tolerate Aftera well. Side effects are generally mild and short-lived. The most common ones include nausea, headache, dizziness, fatigue, breast tenderness, and abdominal cramping. Some people experience light spotting. Your next period may arrive earlier or later than expected, which is a normal response to the hormonal shift the pill causes and not a sign that something went wrong.
How to Know If It Worked
There’s no immediate sign that Aftera was successful. You won’t feel anything specific that confirms it prevented pregnancy. The only reliable way to know is to wait for your period or take a pregnancy test. If your period is more than a week late, or if it doesn’t arrive within three weeks of taking the pill, take a home pregnancy test. For the most accurate result, wait at least one week after a missed period before testing, since testing too early can produce a false negative.
Restarting Regular Birth Control
You can start or resume your regular hormonal birth control (the pill, patch, ring, or shot) immediately after taking Aftera. Taking both at the same time does not reduce the effectiveness of either one. However, you’ll need to use condoms or abstain from sex for seven days after restarting your regular method, since it takes about a week for hormonal contraception to become fully effective again.