Understanding Emergency Contraception
Emergency contraception pills (ECPs), often called the “morning-after pill,” are used to prevent pregnancy after unprotected sex or contraceptive failure. There are two primary types of oral ECPs: those containing levonorgestrel and those with ulipristal acetate. These pills primarily prevent pregnancy by delaying or inhibiting ovulation.
The time an emergency pill remains in the system is influenced by its half-life, which is the time required for the body to eliminate half of the drug. While the contraceptive effect is temporary, trace amounts can persist in the body longer.
Levonorgestrel-based Pills (e.g., Plan B)
Levonorgestrel is a synthetic progestin found in over-the-counter ECPs like Plan B One-Step. Its average half-life is approximately 27.5 hours, meaning half the drug is cleared in that time. Complete elimination typically takes about five half-lives, resulting in clearance within roughly 5 to 6 days. The liver metabolizes the drug, which is then excreted through urine and feces. Levonorgestrel ECPs are most effective within 72 hours (3 days) of unprotected sex, though they can be used up to 5 days, with effectiveness decreasing over time. The drug's presence for several days doesn't equate to continuous pregnancy prevention; its main action is to delay ovulation soon after ingestion.
Ulipristal Acetate-based Pills (e.g., Ella)
Ulipristal acetate (Ella) is a prescription-only ECP that acts as a selective progesterone receptor modulator. It has a half-life of about 32 hours and is generally eliminated from the body within a week. Ella is effective for up to 120 hours (5 days) after unprotected sex, but is most effective when taken as soon as possible.
Factors Affecting How Long the Pill Stays in Your System
Individual factors can influence how the body metabolizes and eliminates ECPs, leading to variations in clearance time.
- Body Mass Index (BMI): Both types of ECPs may be less effective in individuals with higher BMIs. Studies suggest lower levonorgestrel levels in heavier individuals, while ulipristal acetate effectiveness may be reduced for BMIs over 35, without the same effect on drug levels as levonorgestrel.
- Other Medications and Supplements: Certain drugs and herbal supplements can impact ECP metabolism in the liver. For example, substances that induce the CYP3A4 enzyme, involved in metabolizing ECPs, can lower their concentration and effectiveness. St. John's Wort and some anti-seizure medications are examples. Ulipristal acetate interacts with progestin-containing birth control, requiring a waiting period before resuming other hormonal contraception.
- Liver and Kidney Function: Since the liver metabolizes ECPs and the kidneys excrete them, impaired function in these organs can affect how quickly the medication is cleared.
Duration of Side Effects
Most ECP side effects are temporary and typically resolve within 24 to 48 hours. Common immediate side effects include nausea, headaches, abdominal pain, fatigue, and breast tenderness. If vomiting occurs within a few hours of taking a pill, a repeat dose might be necessary. A common, more prolonged effect is a change in the timing, heaviness, or lightness of the next menstrual period. This hormonal response usually corrects itself in the subsequent cycle. A pregnancy test is recommended if your period is delayed by over a week.
Comparison of Emergency Contraceptive Pills
| Feature | Levonorgestrel (e.g., Plan B, Take Action) | Ulipristal Acetate (e.g., Ella) |
|---|---|---|
| Active Ingredient | Levonorgestrel (synthetic progestin) | Ulipristal Acetate (progesterone receptor modulator) |
| Availability | Over-the-counter (OTC) | Prescription only |
| Effective Window | Most effective within 72 hours (3 days), but can be used up to 5 days | Up to 120 hours (5 days) |
| Effectiveness with BMI | Effectiveness may be reduced for those weighing over 165 pounds. | Less effective for those with a BMI of 35 or higher. |
| Approximate Half-Life | ~27.5 hours | ~32 hours |
| Approximate Total Clearance | ~5-6 days | ~7 days |
| Interaction with Hormonal Birth Control | Can be started immediately after taking. | Requires a 5-day wait before starting or resuming. |
Conclusion
Understanding how long an emergency pill stays in your system requires recognizing the difference between the drug's presence and its temporary contraceptive effect. Levonorgestrel is generally cleared within 5 to 6 days. Ulipristal acetate is typically eliminated within a week. Both types are most effective when taken promptly after unprotected sex. While most side effects are short-lived, changes to the menstrual cycle may last longer. ECPs are for emergency use and not a substitute for regular contraception. For questions, consult a healthcare provider. More detailed information on the pharmacology of ECPs can be found on {Link: NIH's National Library of Medicine https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6193352/}.
