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Research · Medication

Emergency contraception

In trials, levonorgestrel prevented about 85% of expected pregnancies, and ulipristal led to fewer pregnancies than levonorgestrel. Both act before ovulation. Levonorgestrel lost much of its effect on the fifth day after sex, and studies disagree on whether higher body weight lowers its effect. Side effects were mild and short: nausea, headache and shifts in the next period.

Add to Bio HackChecked 2026-11-14
Status
Levonorgestrel 1.5 mg (Plan B One-Step and generics such as My Way and Option 2) has been sold over the counter in the US with no age limit since June 20, 2013, to reduce the chance of pregnancy after unprotected sex or a contraceptive failure, taken within 72 hours. Ulipristal acetate 30 mg (ella) is a prescription drug, FDA-approved in 2010 for use within 120 hours. Neither is approved for regular birth control.
Also called
emergency contraceptive pill, morning-after pill, levonorgestrel, levonorgestrel 1.5 mg, Plan B One-Step, Plan B, My Way, Option 2, EContra One-Step, ulipristal acetate, ella, Yuzpe regimen
Taken for
morning-after pill, preventing pregnancy after unprotected sex, birth control failure, broken condom, missed pills, emergency contraception

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help5

Reported risks6

What people take it for, and what was found

Shown to help5

ModerateStudied in women

Preventing pregnancy with levonorgestrel

Shown to prevent about 85% of expected pregnancies after unprotected sex in women, with fewer pregnancies than the older Yuzpe regimen, 1.1% against 3.2%.

Compared with the estrogen and progestin Yuzpe regimen [1][2]; pregnancies expected without emergency contraception [1]; two 0.75 mg doses 12 hours apart [3][2]

The numbers and sources
Effect
Within 72 hours of sex, the pregnancy rate was 1.1% on levonorgestrel and 3.2% on the Yuzpe regimen (RR 0.36, 95% CI 0.18 to 0.70). Levonorgestrel prevented 85% (95% CI 74 to 93) of the pregnancies expected without treatment [1]. Pooled, levonorgestrel led to fewer pregnancies than Yuzpe (RR 0.57, 95% CI 0.39 to 0.84, 6 trials, 4,750 women, high-quality evidence) [2]. A single 1.5 mg dose gave a 1.5% pregnancy rate against 1.8% for two 0.75 mg doses (RR 0.83, 95% CI 0.46 to 1.50) [3], and pooled trials found no clear difference (RR 0.84, 95% CI 0.53 to 1.33) [2].
Population
1,955 women with regular cycles at 21 centers worldwide [1]; 4,071 women at 15 clinics in 10 countries [3]; 115 trials with 60,479 women [2].
Sources
[1], [3], [2]
Caveats
The 85% figure depends on estimating expected pregnancies from cycle dates. A study that dated ovulation with hormone tests put overall efficacy at 68% [4].
ModerateStudied in women

Ulipristal compared with levonorgestrel

Shown to lead to fewer pregnancies than levonorgestrel in women, 1.4% against 2.2% within 72 hours in pooled trials.

Compared with levonorgestrel 1.5 mg [5][2]; pregnancies expected without emergency contraception [6]

The numbers and sources
Effect
In 2 pooled trials, pregnancies within 72 hours occurred in 1.4% on ulipristal and 2.2% on levonorgestrel (OR 0.58, 95% CI 0.33 to 0.99). In the larger trial alone, rates were 1.8% and 2.6% (OR 0.68, 95% CI 0.35 to 1.31) [5]. The Cochrane review found the same direction (RR 0.59, 95% CI 0.35 to 0.99, 2 trials, 3,448 women) [2]. The label reports observed pregnancy rates of 1.9% against 5.6% expected within 72 hours, and 2.2% against 5.5% expected at 48 to 120 hours [6].
Population
2,221 women with regular cycles seeking emergency contraception within 5 days [5]; 2 trials in the Cochrane review [2]; 1,242 and 844 women in the label trials [6].
Sources
[5], [2], [6]
Caveats
The larger trial alone did not reach significance, and it was funded by HRA Pharma [5]. Both pooled analyses rest on the same two trials.
ModerateStudied in women

Taking levonorgestrel sooner after sex

Shown to prevent more pregnancies when taken sooner, with pregnancy odds on day 5 after sex about 6 times those on day 1. Ulipristal rates did not differ by day.

Compared with levonorgestrel taken on the first day after sex [7]; levonorgestrel taken 72 to 120 hours after sex [5]; ulipristal taken in earlier 24-hour windows [6]

The numbers and sources
Effect
Across 4 WHO trials, pregnancy odds on days 2, 3 and 4 did not differ significantly from day 1, and on day 5 the odds ratio was almost 6 [7]. In the earlier WHO trial, efficacy fell as time since sex rose [1]. Between 72 and 120 hours, all 3 pregnancies in the head-to-head trial were in the levonorgestrel group [5]. In the ulipristal label trials, pregnancy rates did not differ across the five 24-hour windows up to 120 hours [6].
Population
6,794 women in 4 WHO trials [7]; 1,955 women [1]; 203 women treated at 72 to 120 hours [5]; pooled ulipristal label trials [6].
Sources
[7], [1], [5], [6]
Caveats
Few women took levonorgestrel on day 5, and it is uncertain whether it still protects then [7]. The over-the-counter label directs taking it within 72 hours [8].
LimitedStudied in women

Taking it before or after ovulation

One study found no pregnancies when women took levonorgestrel before ovulation, against 16 expected, and as many as expected when taken on or after ovulation day.

Compared with pregnancies expected from cycle timing without emergency contraception [4]

The numbers and sources
Effect
Among 103 women who took levonorgestrel 1 to 5 days before ovulation, 16 pregnancies were expected and none occurred. Among 45 who took it on the day of ovulation or after, 8 occurred against 8.7 expected. Overall efficacy was 68% [4]. In the ulipristal label, the dose postponed follicle rupture for at least 5 days in all 8 women dosed before the LH surge and 11 of 14 dosed just before ovulation, and did not when given on the day of the LH peak [6]. FDA concluded in 2022 that Plan B One-Step acts by inhibiting or delaying ovulation, with no direct effect on fertilization or implantation [15].
Population
148 women who had sex in the fertile days, with ovulation dated by hormone and ultrasound measures [4]; 34 women in a pharmacodynamic study [6]; FDA's review of the evidence [15].
Sources
[4], [6], [15]
Caveats
One small study. FDA states that how soon the pill is taken is the most important factor in how well it prevents pregnancy [15].
LimitedStudied in women

Repeated use around sex as regular contraception

Limited evidence: older studies found about 5 pregnancies per 100 woman-years when women took levonorgestrel 0.75 mg around each act of sex, with frequent bleeding changes.

Compared with no comparison group, single-arm studies pooled [17]

The numbers and sources
Effect
The pooled Pearl Index was 5.4 per 100 woman-years for 0.75 mg (95% CI 4.1 to 7.0) and 5.0 for all levonorgestrel doses (95% CI 4.4 to 5.6). Menstrual irregularities were the most common side effect [17].
Population
22 trials with 12,400 women in Europe, Asia and the Americas [17].
Sources
[17]
Caveats
Many studies were decades old with serious methodological issues [17]. The ella label states repeat use within one cycle has not been evaluated [6].

Mixed results1

ModerateStudied in women

Body weight and BMI

Mixed results: two pooled analyses found more pregnancies with higher weight or BMI on levonorgestrel, while two WHO pooled analyses found little or no such trend.

Compared with women with lower weight or BMI taking the same pill [9][10][11][12]; levonorgestrel 3 mg against 1.5 mg in women with obesity [13]

The numbers and sources
Effect
In the ulipristal and levonorgestrel trials pooled, women with obesity had more than 3 times the pregnancy risk of women with normal BMI (OR 3.60, 95% CI 1.96 to 6.53), 4.41 on levonorgestrel and 2.62, not significant, on ulipristal [9]. Pooling 2 trials of levonorgestrel, pregnancy rose from 1.4% at 65 to 75 kg to 6.4% at 75 to 85 kg and 5.7% above 85 kg [10]. Pooling 3 WHO trials, weight and BMI were not linked to pregnancy [11]. Pooling 4 WHO trials, pregnancy was 2.0% at BMI over 30 and 0.7% above 80 kg, and the rise with obesity (OR 8.27) disappeared when one site was excluded [12]. The EMA judged the data too limited to conclude that effect falls with weight and kept both pills for women of all weights [14]. In women with BMI over 30, the ulipristal label reports 3.1% pregnancies against 4.5% expected, and 7.4% against 4.4% expected for levonorgestrel [6]. A double dose of levonorgestrel did not delay follicle rupture more than the standard dose (68.6% against 51.4%, p = 0.14) [13].
Population
women in 2 randomized trials of ulipristal and levonorgestrel [9]; 1,731 women on levonorgestrel [10]; 5,812 women in 3 WHO trials [11]; 6,873 women in 4 WHO trials [12]; 70 women with BMI over 30 and weight of at least 176 lbs [13].
Sources
[9], [10], [11], [12], [14], [6], [13]
Caveats
The WHO trials enrolled mostly African and Asian women, with few at high BMI, and the other pooled trials mostly white women [14][11]. [13] measured ovulation, not pregnancy.

Not shown to help1

ModerateStudied in women

Having pills in advance

Not shown to lower pregnancy rates when women were given pills in advance, though they used them more often and 14.6 hours sooner.

Compared with standard access, by counseling or on request at a clinic or pharmacy [16]

The numbers and sources
Effect
Advance provision did not lower pregnancy rates (OR 1.0, 95% CI 0.78 to 1.29 at 12 months) despite more use (OR 2.52) and faster use (14.6 hours sooner). It did not raise sexually transmitted infections (OR 0.99, 95% CI 0.73 to 1.34), unprotected sex or changes in other contraception [16].
Population
8 trials with 6,389 women in the US, China and India [16].
Sources
[16]
Caveats
The review version sourced is from 2007 [16].

Doses studied

Levonorgestrel was tested as a single 1.5 mg dose or two 0.75 mg doses 12 hours apart, within 72 hours [1] or up to 120 hours after sex [3]. The over-the-counter label is one 1.5 mg tablet as soon as possible within 72 hours [8]. Ulipristal acetate is a single 30 mg tablet within 120 hours, with or without food [6][5]. A 3 mg levonorgestrel dose was tested in women with obesity [13] and in women taking efavirenz or rifampicin [18]. Repeated use studies gave 0.75 mg around each act of sex [17].

Risks

Reported risks6

ModerateVery common

Nausea and vomiting

Nausea affected 23% on levonorgestrel and 12% on ulipristal in trials, less than the 51% on the older Yuzpe regimen.

The numbers and sources
How common
Very common: more than 1 in 10 people.
Effect
Nausea occurred in 23.1% on levonorgestrel and 50.5% on the Yuzpe regimen, and vomiting in 5.6% and 18.8% [1]. Pooled, levonorgestrel had less nausea (RR 0.40, 95% CI 0.36 to 0.44) and vomiting (RR 0.29, 95% CI 0.24 to 0.35) than Yuzpe [2]. Nausea occurred in 12% on ulipristal [6].
Population
1,955 women [1]; trials in the Cochrane review [2]; 2,637 women given ulipristal [6].
Sources
[1], [2], [6]
Caveats
No placebo arm. The labels direct contacting a health professional after vomiting within 2 hours of levonorgestrel or 3 hours of ulipristal [8][6].
ModerateVery common

Headache, abdominal pain, tiredness and dizziness

Headache was the most frequent effect, in about 19% on either ulipristal or levonorgestrel, followed by abdominal pain and nausea in about 12% on ulipristal.

The numbers and sources
How common
Very common: more than 1 in 10 people.
Effect
Headache occurred in 19.3% on ulipristal and 18.9% on levonorgestrel [5]. In the ulipristal trials, headache occurred in 18%, abdominal pain in 12%, nausea in 12%, painful periods in 9%, fatigue in 6% and dizziness in 5% [6]. The levonorgestrel label lists menstrual changes, tiredness, breast pain, nausea, headache, vomiting, lower stomach pain and dizziness, without rates [8].
Population
2,221 women [5]; 2,637 women [6].
Sources
[5], [6], [8]
Caveats
No placebo arm, so the share caused by the pill cannot be told apart from background symptoms.
ModerateStudied in womenVery common

Shift in the next period

Shown to shift the next period, with 19% more than a week late after ulipristal. Periods came later after ulipristal than after levonorgestrel.

The numbers and sources
How common
Very common: more than 1 in 10 people.
Effect
After ulipristal, cycle length rose a mean 2.5 days, 7% had a period more than 7 days early and 19% more than 7 days late, and cycles returned to normal the next month [6]. Ulipristal users were more likely than levonorgestrel users to have their period after the expected date (RR 1.65, 95% CI 1.42 to 1.92) [2]. After levonorgestrel, most women menstruated within 2 days of the expected date [3].
Population
Women in the emergency contraception trials [6][2][3].
Sources
[6], [2], [3]
Caveats
The ella label advises a pregnancy test if the period is more than a week late [6].
LimitedHow often is not known

Drugs that lower the effect

The labels warn that efavirenz, rifampin and seizure drugs may lower the effect. Efavirenz cut levonorgestrel levels 56%, and rifampin cut ulipristal levels over 90%.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
The levonorgestrel label tells people taking efavirenz, rifampin or seizure medicines to ask a doctor or pharmacist first [8]. Efavirenz lowered levonorgestrel exposure 56% (95% CI 49% to 62%) [21]. A 3 mg levonorgestrel dose gave exposure similar to the standard dose in women on efavirenz or rifampicin, while 1.5 mg with efavirenz gave 50% lower exposure [18]. Rifampin lowered ulipristal peak levels 90% and exposure 93%, and the ella label says to avoid CYP3A4 inducers, naming St. John's Wort, phenytoin, carbamazepine, topiramate and others [6].
Population
21 healthy women [21]; 118 women on HIV or tuberculosis treatment [18]; drug level studies [6].
Sources
[8], [21], [18], [6]
Caveats
Drug level studies, not pregnancy outcomes.
LimitedStudied in womenHow often is not known

Ulipristal and starting hormonal birth control

Starting a progestin pill the day after ulipristal raised ovulation within 5 days to 45%, against 3% on ulipristal alone, in one small study.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Ovulation within 5 days occurred in 13 of 29 cycles with desogestrel started the next day and 1 of 29 cycles of ulipristal alone [22]. Starting a combined pill 2 days after ulipristal led to follicle rupture within 5 days in 27% against 3% [6]. The label directs waiting at least 5 days before starting hormonal contraception, with a barrier method until the next period [6].
Population
49 women randomized in a pharmacodynamic study [22]; 33 women in a label study [6].
Sources
[22], [6]
Caveats
Ovulation studies, not pregnancy outcomes.
LimitedStudied in womenHow often is not known

Breastfeeding after ulipristal

The ella label reports a breastfed infant would receive about 1% of the mother's dose over 5 days, with no data on effects in the child.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Measured in breast milk, a fully breastfed infant would receive about 0.8% of the weight-adjusted dose on day 1 and about 1% over 5 days. There is no information on effects in the child or on milk production [6].
Population
12 breastfeeding women [6].
Sources
[6]
Caveats
Drug level data only.

Checked, no increase found2

ModerateStudied in women

Ectopic pregnancy

Not linked to ectopic pregnancy above the general rate. In a systematic review, 3 of 307 pregnancies after levonorgestrel failure were ectopic.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Ectopic pregnancies were 1% of pregnancies after levonorgestrel and 0.6% after mifepristone, no higher than in the general population [19]. The ella label advises checking for ectopic pregnancy in women who become pregnant or have lower abdominal pain after use [6].
Population
136 studies of women treated once with emergency contraceptive pills [19].
Sources
[19], [6]
Caveats
Few pregnancies, so the rate is imprecise [19].
LimitedStudied in pregnancy

Pregnancy after the pill fails

Linked to no rise in malformations or pregnancy complications when levonorgestrel failed, in a cohort of 332 exposed and 332 unexposed pregnancies.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Miscarriage occurred in 31 exposed and 28 unexposed pregnancies, and 4 malformations in each group, with no significant differences in miscarriage, malformation or newborn outcomes [20]. For ulipristal, the label reports 462 pregnancies with known outcomes, 5 infants with anomalies among 84 births, and no pattern of raised risk [6].
Population
664 pregnant women in China [20]; postmarketing pregnancy reports [6].
Sources
[20], [6]
Caveats
Observational data too small to detect rare defects.

Claims tested and not found

  1. That levonorgestrel emergency contraception prevents implantation or ends a pregnancy. Taken on or after ovulation, it left pregnancies at the expected rate [4], and FDA concluded in 2022 that it has no direct effect on fertilization or implantation and will not affect an existing pregnancy [15].
  2. That having emergency pills on hand leads to more unprotected sex or infections. Across 8 trials, advance provision did not raise unprotected sex or sexually transmitted infections [16].
  3. That a double dose of levonorgestrel offsets higher body weight. In women with BMI over 30, 3 mg did not delay follicle rupture more than 1.5 mg [13].
  4. That ectopic pregnancy is more likely when emergency pills fail. The ectopic share of failed pregnancies did not exceed the general population rate [19].

Related

Ulipristal acetateHormonal birth control

Sources

  1. Task Force on Postovulatory Methods of Fertility Regulation. Randomised controlled trial of levonorgestrel versus the Yuzpe regimen of combined oral contraceptives for emergency contraception. The Lancet. 1998. https://doi.org/10.1016/S0140-6736(98)05145-9
  2. Shen J, Che Y, Showell E, Chen K, Cheng L. Interventions for emergency contraception. Cochrane Database of Systematic Reviews. 2019. https://doi.org/10.1002/14651858.cd001324.pub6
  3. von Hertzen H, Piaggio G, Ding J, et al. Low dose mifepristone and two regimens of levonorgestrel for emergency contraception: a WHO multicentre randomised trial. The Lancet. 2002. https://doi.org/10.1016/s0140-6736(02)11767-3
  4. Noé G, Croxatto HB, Salvatierra AM, et al. Contraceptive efficacy of emergency contraception with levonorgestrel given before or after ovulation. Contraception. 2011. https://doi.org/10.1016/j.contraception.2011.03.006
  5. Glasier AF, Cameron ST, Fine PM, et al. Ulipristal acetate versus levonorgestrel for emergency contraception: a randomised non-inferiority trial and meta-analysis. The Lancet. 2010. https://doi.org/10.1016/s0140-6736(10)60101-8
  6. US Food and Drug Administration label. ELLA (ulipristal acetate) tablet, for oral use. DailyMed. 2026. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=2bf93d23-cddd-4613-9066-5b5fa090404b
  7. Piaggio G, Kapp N, von Hertzen H. Effect on pregnancy rates of the delay in the administration of levonorgestrel for emergency contraception: a combined analysis of four WHO trials. Contraception. 2011. https://doi.org/10.1016/j.contraception.2010.11.010
  8. US Food and Drug Administration label. Plan B One-Step (levonorgestrel) tablet, Drug Facts. DailyMed. 2023. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6ce6b40e-14ac-47bd-a648-ddf9e452e559
  9. Glasier A, Cameron ST, Blithe D, et al. Can we identify women at risk of pregnancy despite using emergency contraception? Data from randomized trials of ulipristal acetate and levonorgestrel. Contraception. 2011. https://doi.org/10.1016/j.contraception.2011.02.009
  10. Kapp N, Abitbol JL, Mathé H, et al. Effect of body weight and BMI on the efficacy of levonorgestrel emergency contraception. Contraception. 2015. https://doi.org/10.1016/j.contraception.2014.11.001
  11. Gemzell-Danielsson K, Kardos L, von Hertzen H. Impact of bodyweight/body mass index on the effectiveness of emergency contraception with levonorgestrel: a pooled-analysis of three randomized controlled trials. Current Medical Research and Opinion. 2015. https://doi.org/10.1185/03007995.2015.1094455
  12. Festin MPR, Peregoudov A, Seuc A, Kiarie J, Temmerman M. Effect of BMI and body weight on pregnancy rates with LNG as emergency contraception: analysis of four WHO HRP studies. Contraception. 2017. https://doi.org/10.1016/j.contraception.2016.08.001
  13. Edelman AB, Hennebold JD, Bond K, et al. Double Dosing Levonorgestrel-Based Emergency Contraception for Individuals With Obesity: A Randomized Controlled Trial. Obstetrics & Gynecology. 2022. https://doi.org/10.1097/aog.0000000000004717
  14. European Medicines Agency. Levonorgestrel and ulipristal remain suitable emergency contraceptives for all women, regardless of bodyweight. 2014. https://www.ema.europa.eu/en/news/levonorgestrel-ulipristal-remain-suitable-emergency-contraceptives-all-women-regardless-bodyweight
  15. US Food and Drug Administration. Plan B One-Step (1.5 mg levonorgestrel) Information. https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/plan-b-one-step-15-mg-levonorgestrel-information
  16. Polis CB, Schaffer K, Blanchard K, et al. Advance provision of emergency contraception for pregnancy prevention. Cochrane Database of Systematic Reviews. 2007. https://doi.org/10.1002/14651858.cd005497.pub2
  17. Halpern V, Raymond EG, Lopez LM. Repeated use of pre- and postcoital hormonal contraception for prevention of pregnancy. Cochrane Database of Systematic Reviews. 2014. https://doi.org/10.1002/14651858.cd007595.pub3
  18. Scarsi KK, Smeaton LM, Podany AT, et al. Pharmacokinetics of dose-adjusted levonorgestrel emergency contraception combined with efavirenz-based antiretroviral therapy or rifampicin-containing tuberculosis regimens. Contraception. 2023. https://doi.org/10.1016/j.contraception.2023.109951
  19. Cleland K, Raymond E, Trussell J, Cheng L, Zhu H. Ectopic pregnancy and emergency contraceptive pills: a systematic review. Obstetrics & Gynecology. 2010. https://doi.org/10.1097/aog.0b013e3181dd22ef
  20. Zhang L, Chen J, Wang Y, et al. Pregnancy outcome after levonorgestrel-only emergency contraception failure: a prospective cohort study. Human Reproduction. 2009. https://doi.org/10.1093/humrep/dep076
  21. Carten ML, Kiser JJ, Kwara A, Mawhinney S, Cu-Uvin S. Pharmacokinetic interactions between the hormonal emergency contraception, levonorgestrel (Plan B), and efavirenz. Infectious Diseases in Obstetrics and Gynecology. 2012. https://doi.org/10.1155/2012/137192
  22. Brache V, Cochon L, Duijkers IJ, et al. A prospective, randomized, pharmacodynamic study of quick-starting a desogestrel progestin-only pill following ulipristal acetate for emergency contraception. Human Reproduction. 2015. https://doi.org/10.1093/humrep/dev241

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