The morning after pill is a form of emergency contraception used to prevent pregnancy after unprotected sexual intercourse or when a primary birth control method has failed. Understanding how this medication functions and its duration within the body can provide clarity for individuals considering or using it.
How the Morning After Pill Works
The primary way the morning after pill works is by preventing or delaying ovulation, which is the release of an egg from the ovary. If an egg is not released, fertilization cannot occur, thus preventing pregnancy. The medication does not end an existing pregnancy.
Two main active ingredients are used in these pills: levonorgestrel and ulipristal acetate. Levonorgestrel-based pills, often sold under brand names like Plan B One-Step, primarily exert their effect by delaying the luteinizing hormone surge, which in turn delays ovulation. Ulipristal acetate, marketed as ella, is a selective progesterone receptor modulator that also works by inhibiting or delaying ovulation.
How Long the Active Ingredient Stays in Your System
The duration an active ingredient from the morning after pill remains in the body depends on the specific medication. Levonorgestrel, found in many over-the-counter options, has an elimination half-life typically ranging from approximately 20 to 32 hours. This means that about half of the drug is cleared from the bloodstream within that timeframe. Its effectiveness in preventing pregnancy is highest when taken within 72 hours of unprotected sex, with efficacy decreasing significantly after 24 hours.
Ulipristal acetate, a prescription-only option, has a half-life of approximately 32.4 hours. Ulipristal acetate remains effective for a longer window, up to 120 hours (five days) after unprotected intercourse, and maintains higher efficacy compared to levonorgestrel as time passes within this window. Individual metabolism can lead to slight variations in how quickly these medications are processed and eliminated from the body.
How Long Side Effects Typically Last
After taking the morning after pill, individuals may experience various temporary side effects. Common reactions include nausea, vomiting, headaches, dizziness, fatigue, and breast tenderness. Abdominal pain or cramping is also frequently reported.
These side effects are generally mild and short-lived, often resolving within a few hours to a couple of days, typically within 24 to 48 hours. Light vaginal bleeding or spotting between periods is also a common side effect due to hormonal changes, which is not a menstrual period. If vomiting occurs within two to three hours of taking the pill, it is advisable to consult a healthcare provider, as another dose might be necessary to ensure effectiveness. Severe or prolonged side effects, especially intense abdominal pain or very heavy vaginal bleeding, should prompt medical attention, as these could indicate a more serious condition like an ectopic pregnancy.
What to Expect After Taking the Pill
Beyond the immediate side effects, the morning after pill can influence the timing and characteristics of your next menstrual period. It is common for the subsequent period to be earlier, later, heavier, lighter, or to include more spotting than usual. These changes are typically temporary, and the menstrual cycle generally returns to its regular pattern by the following month.
If your period is delayed by more than one week (seven days) or if it does not occur within three weeks of taking the emergency contraception, it is recommended to take a pregnancy test. The morning after pill is a one-time emergency measure and does not provide ongoing protection against pregnancy. It also does not protect against sexually transmitted infections. For continued pregnancy prevention, discussing regular birth control options with a healthcare provider is an important next step.