Emergency contraception, often called the “morning-after pill,” is a backup method to prevent pregnancy after unprotected sex or contraceptive failure. Plan B One-Step, a common form, contains levonorgestrel. It is for emergency use and not a substitute for regular birth control. Taking it as soon as possible offers the greatest chance of preventing pregnancy.
How Emergency Contraception Works
Levonorgestrel-based emergency contraception primarily functions by delaying or preventing ovulation, the release of an egg from the ovary. This hormonal intervention interferes with the luteinizing hormone (LH) surge, which triggers ovulation. By preventing the egg’s release, there is no egg available for sperm to fertilize. It does not terminate an existing pregnancy and will not work if a fertilized egg has already implanted in the uterus. It does not affect implantation or the maintenance of a pregnancy after implantation has occurred.
Addressing Multiple Ejaculations
The effectiveness of levonorgestrel emergency contraception, such as Plan B, is not directly influenced by the number of ejaculations during a single unprotected sexual encounter. The medication’s mechanism centers on preventing or delaying ovulation, not neutralizing sperm. Sperm can persist in the reproductive tract for up to five days. Emergency contraception works by attempting to prevent the release of an egg during this window. The critical factor for its effectiveness is whether ovulation has occurred before the medication is taken, not the volume or frequency of sperm exposure.
Key Factors Influencing Effectiveness
The timing of administration significantly impacts the effectiveness of levonorgestrel emergency contraception. It is most effective when taken as soon as possible, ideally within 72 hours (three days) of unprotected sex, though it can be taken up to 120 hours (five days). If ovulation has already occurred before the pill is taken, it will not be effective.
Body weight can also play a role. Some studies suggest reduced effectiveness in individuals with a body weight of 155 pounds or more, or a BMI of 30 or higher. While there is no official weight limit on the FDA label for Plan B, it is still considered safe for use by individuals in higher weight categories. Alternative emergency contraception options like ulipristal acetate or copper IUDs may offer higher efficacy for these individuals.
Certain medications can reduce the effectiveness of levonorgestrel emergency contraception. These include:
Anti-seizure drugs (e.g., carbamazepine, phenytoin, topiramate)
The antibiotic rifampin
The antifungal griseofulvin
The herbal supplement St. John’s Wort
These medications accelerate the metabolism of levonorgestrel, leading to lower concentrations. Individuals taking such medications should consult a healthcare provider to discuss alternatives.
Next Steps After Taking Emergency Contraception
After taking levonorgestrel emergency contraception, individuals may experience temporary side effects. Common side effects include nausea, headache, dizziness, abdominal pain, breast tenderness, and fatigue. Changes to the next menstrual period are also common, such as an earlier, later, heavier, or lighter period. These menstrual changes typically resolve by the subsequent cycle.
Take a pregnancy test if your next period is delayed by more than a week. Severe lower abdominal pain three to five weeks after taking the medication could indicate an ectopic pregnancy, requiring immediate medical attention. Emergency contraception is not a form of regular birth control and does not offer protection against sexually transmitted infections. Consulting a healthcare provider for ongoing contraception options and any persistent concerns is recommended.