Table of ContentsView AllTable of ContentsEffectivenessDosageHow Long Till It Works?PrecautionsOther Birth Control MethodsMost Effective MethodFrequently Asked Questions
Table of ContentsView All
View All
Table of Contents
Effectiveness
Dosage
How Long Till It Works?
Precautions
Other Birth Control Methods
Most Effective Method
Frequently Asked Questions
There isn’t a limit to how many times you can use theemergency contraceptivepill Plan B.
Plan B, the morning-after pill, prevents pregnancy after unprotected sex. Plan B One-Step consists of a single dose of a synthetic (made in a lab)progestinhormone called levonorgestrel.
Here’s the latest evidence about Plan B’s effectiveness and some precautions to remember, along with a summary of other contraceptive options to help you make an informed decision.
Emergency contraceptive tablet.SOPA Images / Getty Images
SOPA Images / Getty Images
How Effective Is Plan B?
In clinical trials, between 0.6% and 3.1% of people who usedPlan Bbecame pregnant.To put this in perspective, there is a 4% to 5% chance of becoming pregnant anytime you have sex, and this rate jumps to 30% around the time of ovulation.
Plan B is most effective when it’s taken as soon as possible after unprotected intercourse. For it to work, it must be taken within 96 hours (four days) of sex. It may even work for up to 120 hours (five days), but more research is needed to know for sure.
The effectiveness of Plan B decreases over time. It’s 5 times as effective at preventing pregnancy if it’s taken during the first 24 hours after sex than it is after 96 hours.
Effectiveness also depends on the timing of the menstrual cycle. Plan B works if it’s taken before ovulation occurs.Once an embryo has been implanted in the uterus, Plan B will not be effective, and the pregnancy will continue.
The older version of Plan B contained two 0.75 mg levonorgestrel tablets to be taken twelve hours apart. This two-step product is no longer available in the United States.
If vomiting occurs within three hours of taking Plan B, you should take another Plan B pill.
If you have unprotected sex within 24 hours of taking Plan B, you don’t need to retake it, but anytime after that first 24 hours, you should take another Plan B pill to be safe.
How Long Does Plan B Take to Work?
Plan B starts to work quickly. On average, it reaches the highest concentration in the body within about two hours.
A significant drawback to Plan B is that it is less effective for people with abody mass index(BMI) of over 25 and for those who weigh more than 154 pounds.
In one large study of females who took Plan B, those who weighed more than 165 pounds had about a 6% pregnancy rate vs. a 1.5% rate for those weighing less than 165 pounds.
Side effects associated with Plan B include:
Note that Plan B may interact with prescription medications in several ways. Medicines like the following lower the amount of Plan B in the body and can decrease its effects:
Plan B increases the amount of some medications and can increase the risk of their side effects. These drugs include the following:
What Are Other Birth Control Methods?
Birth control methods include emergency contraceptives and regular (ongoing) methods. There are manyoptionsdepending on your needs and lifestyle.
Otheremergency birth control methodsavailable in the United States include intrauterine devices and the tablet Ella (ulipristal acetate).
However, the Food and Drug Administration (FDA) has not approved intrauterine devices.Here are the alternatives to Plan B One-Step:
Copper Intrauterine Device (IUD)
CopperIUDsare the most effective form of emergency birth control. The pregnancy rate with a copper IUD is very low, at 0.09%.
A healthcare provider must place these IUDs into the uterus within five days of unprotected sex.
Levonorgestrel IUD
This hormone-based IUD (brand names includeLilettaandMirena) gradually releases 52 mg of levonorgestrel over several years. A healthcare provider must place it in the uterus within five days of unprotected sex. It is not quite as effective as the copper IUD, though it still has a low pregnancy rate of 0.5%.
Keep in mind that if you become pregnant while an IUD is implanted, there is a possibility of the followingrisks:
Ella (Ulipristal Acetate)
Ulipristal acetate is more effective than Plan B. The pregnancy rate for people who use this product is 0.9% to 1.8%. Studies have shown a 65% lower pregnancy rate for people taking ulipristal acetate than Plan B within 24 hours of intercourse.
Yuzpe Method
Continuous Birth Control
Regular hormonal birth control methods are more effective than emergency contraception.These can include:
Barrier methods likecondomsand planning based on your menstrual cycle (often called therhythm method) have also been used to prevent pregnancy. Note the rhythm method, or fertility awareness methods, are between 77% and 98% effective and require great persistence and attention to detail to prevent pregnancy.
What Is the Most Effective Birth Control Method?
The copper IUD is the most effective method of emergency contraception, resulting in virtually no pregnancies if inserted within five days of unprotected sex.The levonorgestrel IUD has similar effectiveness.Remember that IUDs are typically more expensive and require an office or clinic visit for device placement.
In terms of the pills available, Ella is more effective than Plan B, but it requires a prescription and may not be readily available at all pharmacies.
Summary
It is most effective right after unprotected sex, and its effectiveness decreases over time. It won’t work if it’s taken more than four or five days after intercourse.
Several medicines, including some used for epilepsy, lower the effectiveness of Plan B.
It’s best for people with a BMI less than 25 and less effective for people with higher BMIs.
Other options for emergency birth control are more effective, but they also have more barriers to use. These include copper and hormonal IUDs and the prescription Ella.
You can take Plan B as often as you need it. There’s no evidence that using it often, even more than once in the same menstrual cycle, is dangerous.
Plan B works within three hours of taking it.
14 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Jatlaoui TC, Riley H, Curtis KM.Safety data for levonorgestrel, ulipristal acetate and Yuzpe regimens for emergency contraception.Contraception. 2016;93(2):93-112. doi:10.1016/j.contraception.2015.11.001Salcedo J, Cleland K, Bartz D, et al.Society of Family Planning clinical recommendations: Emergency contraception.Contraception. Published online January 2023:109958. doi:10.1016/j.contraception.2023.109958Cleland K, Raymond EG, Westley E, et al.Emergency contraception review: evidence-based recommendations for clinicians.Clin Obstet Gynecol. 2014;57(4):741-750. doi:10.1097/GRF.0000000000000056Bullock H, Salcedo J.Emergency contraception: do your patients have a Plan B?.Obstet Gynecol Clin North Am. 2015;42(4):699-712. doi:10.1016/j.ogc.2015.08.003Piaggio 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;84(1):35-39. doi:10.1016/j.contraception.2010.11.010Haeger KO, Lamme J, Cleland K.State of emergency contraception in the U.S., 2018.Contracept Reprod Med. 2018;3:20. doi:10.1186/s40834-018-0067-8Matyanga CMJ, Dzingirai B.Clinical pharmacology of hormonal emergency contraceptive pills.Int J Reprod Med. 2018;2018:2785839. doi:10.1155/2018/2785839Kapp N, Abitbol JL, Mathé H, et al.Effect of body weight and BMI on the efficacy of levonorgestrel emergency contraception.Contraception. 2015;91(2):97-104. doi:10.1016/j.contraception.2014.11.001Le Corvaisier C, Capelle A, France M, et al.Drug interactions between emergency contraceptive drugs and cytochrome inducers: literature review and quantitative prediction.Fundam Clin Pharmacol. 2021;35(2):208-216. doi:10.1111/fcp.12601Turok DK, Gero A, Simmons RG, et al.Levonorgestrel vs. Copper Intrauterine Devices for Emergency Contraception.N Engl J Med. 2021;384(4):335-344. doi:10.1056/NEJMoa2022141Black KI, Hussainy SY.Emergency contraception: Oral and intrauterine options.Aust Fam Physician. 2017;46(10):722-726.ESHRE CapriWorkshop Group.Emergency contraception. Widely available and effective but disappointing as a public health intervention: a review.Hum Reprod. 2015;30(4):751-760. doi:10.1093/humrep/dev019Colquitt CW, Martin TS.Contraceptive methods.J Pharm Pract. 2017;30(1):130-135. doi:10.1177/0897190015585751Planned Parenthood.Fertility awareness.
14 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Jatlaoui TC, Riley H, Curtis KM.Safety data for levonorgestrel, ulipristal acetate and Yuzpe regimens for emergency contraception.Contraception. 2016;93(2):93-112. doi:10.1016/j.contraception.2015.11.001Salcedo J, Cleland K, Bartz D, et al.Society of Family Planning clinical recommendations: Emergency contraception.Contraception. Published online January 2023:109958. doi:10.1016/j.contraception.2023.109958Cleland K, Raymond EG, Westley E, et al.Emergency contraception review: evidence-based recommendations for clinicians.Clin Obstet Gynecol. 2014;57(4):741-750. doi:10.1097/GRF.0000000000000056Bullock H, Salcedo J.Emergency contraception: do your patients have a Plan B?.Obstet Gynecol Clin North Am. 2015;42(4):699-712. doi:10.1016/j.ogc.2015.08.003Piaggio 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;84(1):35-39. doi:10.1016/j.contraception.2010.11.010Haeger KO, Lamme J, Cleland K.State of emergency contraception in the U.S., 2018.Contracept Reprod Med. 2018;3:20. doi:10.1186/s40834-018-0067-8Matyanga CMJ, Dzingirai B.Clinical pharmacology of hormonal emergency contraceptive pills.Int J Reprod Med. 2018;2018:2785839. doi:10.1155/2018/2785839Kapp N, Abitbol JL, Mathé H, et al.Effect of body weight and BMI on the efficacy of levonorgestrel emergency contraception.Contraception. 2015;91(2):97-104. doi:10.1016/j.contraception.2014.11.001Le Corvaisier C, Capelle A, France M, et al.Drug interactions between emergency contraceptive drugs and cytochrome inducers: literature review and quantitative prediction.Fundam Clin Pharmacol. 2021;35(2):208-216. doi:10.1111/fcp.12601Turok DK, Gero A, Simmons RG, et al.Levonorgestrel vs. Copper Intrauterine Devices for Emergency Contraception.N Engl J Med. 2021;384(4):335-344. doi:10.1056/NEJMoa2022141Black KI, Hussainy SY.Emergency contraception: Oral and intrauterine options.Aust Fam Physician. 2017;46(10):722-726.ESHRE CapriWorkshop Group.Emergency contraception. Widely available and effective but disappointing as a public health intervention: a review.Hum Reprod. 2015;30(4):751-760. doi:10.1093/humrep/dev019Colquitt CW, Martin TS.Contraceptive methods.J Pharm Pract. 2017;30(1):130-135. doi:10.1177/0897190015585751Planned Parenthood.Fertility awareness.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Jatlaoui TC, Riley H, Curtis KM.Safety data for levonorgestrel, ulipristal acetate and Yuzpe regimens for emergency contraception.Contraception. 2016;93(2):93-112. doi:10.1016/j.contraception.2015.11.001Salcedo J, Cleland K, Bartz D, et al.Society of Family Planning clinical recommendations: Emergency contraception.Contraception. Published online January 2023:109958. doi:10.1016/j.contraception.2023.109958Cleland K, Raymond EG, Westley E, et al.Emergency contraception review: evidence-based recommendations for clinicians.Clin Obstet Gynecol. 2014;57(4):741-750. doi:10.1097/GRF.0000000000000056Bullock H, Salcedo J.Emergency contraception: do your patients have a Plan B?.Obstet Gynecol Clin North Am. 2015;42(4):699-712. doi:10.1016/j.ogc.2015.08.003Piaggio 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;84(1):35-39. doi:10.1016/j.contraception.2010.11.010Haeger KO, Lamme J, Cleland K.State of emergency contraception in the U.S., 2018.Contracept Reprod Med. 2018;3:20. doi:10.1186/s40834-018-0067-8Matyanga CMJ, Dzingirai B.Clinical pharmacology of hormonal emergency contraceptive pills.Int J Reprod Med. 2018;2018:2785839. doi:10.1155/2018/2785839Kapp N, Abitbol JL, Mathé H, et al.Effect of body weight and BMI on the efficacy of levonorgestrel emergency contraception.Contraception. 2015;91(2):97-104. doi:10.1016/j.contraception.2014.11.001Le Corvaisier C, Capelle A, France M, et al.Drug interactions between emergency contraceptive drugs and cytochrome inducers: literature review and quantitative prediction.Fundam Clin Pharmacol. 2021;35(2):208-216. doi:10.1111/fcp.12601Turok DK, Gero A, Simmons RG, et al.Levonorgestrel vs. Copper Intrauterine Devices for Emergency Contraception.N Engl J Med. 2021;384(4):335-344. doi:10.1056/NEJMoa2022141Black KI, Hussainy SY.Emergency contraception: Oral and intrauterine options.Aust Fam Physician. 2017;46(10):722-726.ESHRE CapriWorkshop Group.Emergency contraception. Widely available and effective but disappointing as a public health intervention: a review.Hum Reprod. 2015;30(4):751-760. doi:10.1093/humrep/dev019Colquitt CW, Martin TS.Contraceptive methods.J Pharm Pract. 2017;30(1):130-135. doi:10.1177/0897190015585751Planned Parenthood.Fertility awareness.
Jatlaoui TC, Riley H, Curtis KM.Safety data for levonorgestrel, ulipristal acetate and Yuzpe regimens for emergency contraception.Contraception. 2016;93(2):93-112. doi:10.1016/j.contraception.2015.11.001
Salcedo J, Cleland K, Bartz D, et al.Society of Family Planning clinical recommendations: Emergency contraception.Contraception. Published online January 2023:109958. doi:10.1016/j.contraception.2023.109958
Cleland K, Raymond EG, Westley E, et al.Emergency contraception review: evidence-based recommendations for clinicians.Clin Obstet Gynecol. 2014;57(4):741-750. doi:10.1097/GRF.0000000000000056
Bullock H, Salcedo J.Emergency contraception: do your patients have a Plan B?.Obstet Gynecol Clin North Am. 2015;42(4):699-712. doi:10.1016/j.ogc.2015.08.003
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;84(1):35-39. doi:10.1016/j.contraception.2010.11.010
Haeger KO, Lamme J, Cleland K.State of emergency contraception in the U.S., 2018.Contracept Reprod Med. 2018;3:20. doi:10.1186/s40834-018-0067-8
Matyanga CMJ, Dzingirai B.Clinical pharmacology of hormonal emergency contraceptive pills.Int J Reprod Med. 2018;2018:2785839. doi:10.1155/2018/2785839
Kapp N, Abitbol JL, Mathé H, et al.Effect of body weight and BMI on the efficacy of levonorgestrel emergency contraception.Contraception. 2015;91(2):97-104. doi:10.1016/j.contraception.2014.11.001
Le Corvaisier C, Capelle A, France M, et al.Drug interactions between emergency contraceptive drugs and cytochrome inducers: literature review and quantitative prediction.Fundam Clin Pharmacol. 2021;35(2):208-216. doi:10.1111/fcp.12601
Turok DK, Gero A, Simmons RG, et al.Levonorgestrel vs. Copper Intrauterine Devices for Emergency Contraception.N Engl J Med. 2021;384(4):335-344. doi:10.1056/NEJMoa2022141
Black KI, Hussainy SY.Emergency contraception: Oral and intrauterine options.Aust Fam Physician. 2017;46(10):722-726.
ESHRE CapriWorkshop Group.Emergency contraception. Widely available and effective but disappointing as a public health intervention: a review.Hum Reprod. 2015;30(4):751-760. doi:10.1093/humrep/dev019
Colquitt CW, Martin TS.Contraceptive methods.J Pharm Pract. 2017;30(1):130-135. doi:10.1177/0897190015585751
Planned Parenthood.Fertility awareness.
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