Aftera is a brand of levonorgestrel emergency contraception, a progestin-only pill used after unprotected intercourse to prevent pregnancy. It is often called the “morning-after pill,” though it is effective for up to 72 hours following sex. Aftera prevents pregnancy from beginning; it does not terminate an established pregnancy. Its function depends entirely on the timing of the menstrual cycle, specifically the moment of ovulation.
The Mechanism: How Aftera Prevents Pregnancy
The primary mechanism of levonorgestrel is to disrupt the natural hormonal cascade that leads to the release of an egg. This single, high dose of a synthetic hormone suppresses the release of the Luteinizing Hormone (LH) from the pituitary gland.
The LH surge is the specific hormonal signal that triggers the ovary to release a mature egg. By suppressing or delaying this surge, levonorgestrel prevents the egg from being released. Since sperm can survive in the reproductive tract for up to five days, delaying ovulation allows the sperm to die before an egg is available for fertilization. The pill’s effectiveness is almost entirely dependent on this anti-ovulatory action.
If the egg is never released from the ovary, fertilization cannot occur. Levonorgestrel does not interfere with sperm function, nor does it prevent a fertilized egg from implanting in the uterine wall. This focus on preventing the release of the egg defines its function and its limitations during the actual ovulation period.
The Ovulation Threshold: Why Timing Is Critical
Aftera’s effectiveness is directly tied to the start of the LH surge. Once the level of Luteinizing Hormone has already begun to rise significantly, the levonorgestrel pill is no longer able to interrupt the hormonal sequence leading to egg release. Studies show that if levonorgestrel is administered after the LH surge has started, it is largely ineffective at preventing ovulation.
The pill is designed to prevent ovulation, so once that event has occurred, the medication has no biological target remaining. If the egg has already been released, it is available to be fertilized by any present sperm. At this point, Aftera cannot stop fertilization or prevent a fertilized egg from implanting in the uterus. Therefore, if a person has already ovulated, Aftera will not work to prevent pregnancy.
Pinpointing the exact moment of ovulation can be difficult, making the pill’s timing urgent. The effectiveness of levonorgestrel declines substantially the closer a person is to the point of ovulation. This is why the medication is most effective when taken as soon as possible after unprotected sex, ideally within the first 24 hours, well before the fertile window closes.
Options When Aftera Is No Longer Effective
When there is concern that ovulation may have already occurred, or if a person is beyond the 72-hour window for levonorgestrel, alternative emergency contraception methods should be considered. One option is Ulipristal Acetate (brand name Ella), which is a different type of hormonal pill. Ulipristal acetate is more effective than levonorgestrel because it can delay ovulation even after the LH surge has begun, though not after the LH peak.
Ulipristal acetate remains effective for up to 120 hours (five days) after unprotected sex, and its efficacy does not decline over that period. However, both levonorgestrel and ulipristal acetate rely on preventing ovulation, meaning they are ineffective once the egg has been released.
Copper IUD
The most effective option for emergency contraception, regardless of the cycle timing, is the Copper Intrauterine Device (IUD). The Copper IUD can be inserted up to five days after unprotected sex. It works by creating a toxic environment for both sperm and eggs, preventing fertilization. Unlike hormonal pills, the Copper IUD’s mechanism is not dependent on suppressing ovulation, making it highly effective even when ovulation has already occurred.
Weight Limitations
Another factor that can make Aftera less effective is body weight. Studies suggest that levonorgestrel may be less effective in individuals who weigh over 155 pounds or have a Body Mass Index (BMI) above 25. In these cases, Ulipristal Acetate or the Copper IUD are generally recommended due to their sustained effectiveness regardless of weight.