How long does the morning after pill last in your system?

October 10, 2025 •

4 min read

The half-life of a levonorgestrel-based morning after pill is around 24 to 27.5 hours, meaning it takes over a day for half the drug to be metabolized. This duration is key to understanding how long the morning after pill lasts in your system, but the medication's effectiveness is highest much sooner after unprotected sex.

Quick Summary

The morning after pill's duration depends on its active ingredient, typically clearing within days. Its protective effect is highest soon after intake, fading as it's metabolized and excreted.

Key Points

Half-Life vs. Effectiveness: A morning after pill's half-life determines how long it takes to clear the system (typically 5-6 days), but its peak effectiveness is within the first 24 hours.
Different Pill Types, Different Rules: Levonorgestrel-based pills (like Plan B) have a shorter effective window (72 hours) and are less effective for higher body weights than prescription ulipristal acetate (ella®), which works for up to 120 hours.
Factors Impacting Duration: Individual metabolism, body weight, liver function, and other medications (like St. John's Wort or certain antibiotics) can affect how quickly the pill is processed.
Temporary Side Effects: Common side effects such as nausea, headaches, and breast tenderness typically resolve within 24-48 hours, though menstrual cycle changes can last longer.
Menstrual Cycle Disruption: The high dose of hormones can cause your next period to be early, late, or irregular, but your cycle usually returns to normal the following month.
Emergency Use Only: The morning after pill is not a substitute for regular birth control and only prevents pregnancy from a single instance of unprotected sex.

The morning after pill, also known as emergency contraception (EC), is a medication taken after unprotected sex or contraceptive failure to prevent pregnancy. There are two primary types of EC pills available: levonorgestrel-based and ulipristal acetate-based. The time these medications remain in your system and their effective window can differ significantly, and it is crucial to understand these distinctions.

Types of Morning After Pills and Their Duration

The duration of the morning after pill in your body is determined by its active ingredient. The two main types, levonorgestrel and ulipristal acetate, have different half-lives, which dictate how long they take to be eliminated.

Levonorgestrel-Based Pills (Plan B, Take Action, etc.)

Levonorgestrel is a synthetic progestin hormone that works primarily by preventing or delaying ovulation. It is the active ingredient in many over-the-counter EC pills. The typical half-life of levonorgestrel is approximately 24 to 27.5 hours. A drug is generally considered fully eliminated from the body after about five half-lives. For levonorgestrel, this means it is mostly cleared from your system within about 5 to 6 days.

It is important to note that while the medication may be detectable for several days, its effectiveness at preventing pregnancy diminishes over time. Its highest efficacy is within the first 24 hours of unprotected sex, with effectiveness significantly reduced beyond 72 hours. Levonorgestrel is metabolized in the liver and eliminated from the body through urine and feces.

Ulipristal Acetate (ella®)

Ulipristal acetate is a selective progesterone receptor modulator that requires a prescription. It is effective for a longer period than levonorgestrel, up to 120 hours (five days) after unprotected sex. Its half-life is around 32 hours. Like levonorgestrel, it is metabolized by the liver and has an active metabolite, mono-demethyl-ulipristal acetate. It is primarily excreted through the feces.

Because of its mechanism of action, ulipristal can prevent ovulation even closer to the expected time of ovulation than levonorgestrel. This makes it a more consistent option for preventing pregnancy throughout the five-day window. After a single dose, it is effectively eliminated from the body within about 5 to 6 days, though small amounts may be present for slightly longer.

Factors Influencing How Long the Pill Stays in Your System

Several factors can influence the rate at which your body processes and eliminates emergency contraception. These variations mean the exact duration of the medication's presence and its side effects can vary from person to person.

Individual Metabolism: Everyone's body metabolizes medications at a different rate. Factors such as genetics, age, and liver function can affect how quickly the active hormones are processed and cleared.
Body Weight and BMI: Higher body weight and Body Mass Index (BMI) have been shown to impact the effectiveness of both types of pills, with levonorgestrel being more affected. The concentration of the drug and its clearance can be altered, potentially reducing efficacy, but not necessarily lengthening the duration in the system.
Medication Interactions: Certain medications and herbal supplements can interfere with the metabolism of EC pills. For example, drugs that induce the CYP3A4 enzyme in the liver (like certain antibiotics, anti-seizure medications, and St. John's Wort) can cause the pill to be metabolized and cleared more quickly, reducing its effectiveness.
Vomiting: If you vomit within a few hours of taking the pill, a significant portion of the dose may not be absorbed, requiring another dose.

Comparison of Levonorgestrel and Ulipristal Acetate


Feature	Levonorgestrel (Plan B)	Ulipristal Acetate (ella®)
Active Ingredient	Levonorgestrel	Ulipristal Acetate
Availability	Over-the-counter	Prescription only
Time Window	Most effective within 72 hours (3 days), but can be used up to 120 hours (5 days) with reduced efficacy.	Up to 120 hours (5 days).
Mechanism	Delays or prevents ovulation.	Delays or prevents ovulation; may also interfere with implantation.
Effectiveness with Weight	Decreased effectiveness for individuals over 165 lbs.	More effective for individuals over 165 lbs compared to levonorgestrel, but still less effective over 195 lbs.
Half-Life	24-27.5 hours.	32-32.4 hours.
Typical Duration in System	~5-6 days until fully cleared.	~5-6 days until fully cleared.

Duration of Side Effects

While the active components of the pill are cleared from your body within about a week, any side effects are generally shorter-lived. The influx of hormones can cause temporary symptoms that typically resolve within a couple of days.

Common side effects and their typical duration include:

Nausea and abdominal pain: Often subsides within 24 hours.
Fatigue, headache, dizziness: Usually last for a couple of days.
Breast tenderness: Can persist for a few days.
Menstrual changes: Your next period may come earlier or later, be heavier or lighter, or include spotting. These irregularities typically last for only one cycle.

It is important to note that if severe abdominal pain or persistent bleeding occurs, especially 3 to 5 weeks after taking the pill, you should seek medical attention to rule out complications like an ectopic pregnancy.

Conclusion

The time it takes for the morning after pill to leave your system depends on the type of medication taken. Levonorgestrel and ulipristal acetate both have half-lives of over 24 hours and are typically fully eliminated within about 5 to 6 days. While the medication's presence may linger, its highest period of effectiveness is immediately after intake, decreasing with each passing hour. Factors such as individual metabolism, weight, and other medications can influence this timeline and the pill's overall efficacy. Any temporary side effects like nausea or menstrual changes usually pass within a few days, and your cycle should return to normal within a month. For ongoing protection, emergency contraception should not be used as a regular form of birth control. If you have concerns about the medication or experience prolonged side effects, it is always recommended to consult a healthcare provider.

For more detailed pharmacological information on levonorgestrel, you can refer to the NCBI Bookshelf entry.

Frequently Asked Questions

No, the morning after pill does not stay in your system permanently. Its active ingredients, such as levonorgestrel or ulipristal acetate, are processed by the liver and eliminated from the body over a period of days, typically being fully cleared within about a week.

There is no way to know if the pill is still 'active' or effective after a certain period of time has passed. Its highest efficacy is immediately after taking it, and this protection wanes as time goes on. The only way to confirm if it was successful is to wait for your next period to arrive on time. If your period is more than a week late, take a pregnancy test.

Yes, it is very common for the morning after pill to temporarily affect your next period. It may cause your period to arrive earlier, later, be heavier or lighter than usual, or cause spotting between cycles. For most people, their cycle returns to normal the following month.

Side effects like nausea, headaches, dizziness, and fatigue are typically mild and short-lived, usually resolving within 24 to 48 hours. Menstrual cycle changes are the longest-lasting side effect, usually only affecting the next cycle.

While body weight can affect the effectiveness of the morning after pill, particularly levonorgestrel, it doesn't significantly alter the total clearance time. However, a higher BMI may mean reduced efficacy and a less predictable response to the medication.

You can take another dose of the same type of morning after pill if another instance of unprotected sex occurs. However, it's not recommended for routine use as it is less effective and has a higher failure rate than regular birth control. For ulipristal acetate (ella®), you should not take a levonorgestrel pill within 5 days of taking ella®.

The active ingredients are metabolized by the liver, then their metabolites are excreted primarily through the kidneys (in urine) and the digestive system (in feces).