How effective is Plan B, and how long is it effective for?

How does Plan B work? | Efficacy | Contraindications | Interactions | How to tell if Plan B did not work | How long is Plan B effective? | Can pregnancy still occur? | Where to buy Plan B | FAQs

Whether you forgot to take the pill or the condom broke, you still have an option for preventing pregnancy—but you have to act fast. Plan B One-Step is a morning-after pill that can prevent pregnancy after unprotected sex or birth control failure. Emergency contraception can offer peace of mind, but many women still wonder: how effective is Plan B?

How does Plan B work?

Plan B is a progesterone drug that contains the hormone levonorgestrel. Levonorgestrel prevents pregnancy in different ways, depending on where you are in your menstrual cycle. It can temporarily stop the release of an egg from an ovary (ovulation) or prevent the sperm and egg from joining together (fertilization). It may also alter the endometrium so that a fertilized egg cannot implant in the uterus. Plan B should be taken within 72 hours after a regular birth control method fails or within 72 hours after unprotected intercourse.

Once Plan B absorbs into the bloodstream, which usually takes a couple of hours, levonorgestrel starts to affect the ovaries or uterine lining. Although it’s rare, some women may throw up within two hours of taking a Plan B pill. If this happens to you, it’s best to follow up with your healthcare provider and ask whether or not you should take a second dose. 

You can take Plan B at any time during your cycle, but it’s only meant to be used as an emergency contraceptive pill. Because taking an emergency contraceptive affects your hormones, it can often cause side effects. Here are some of the most common side effects that women experience from Plan B:

• Nausea
• Lower abdominal pain
• Breast tenderness 
• Fatigue
• Heavier menstrual bleeding
• Delayed menses
• Dizziness
• Headache 

If you’ve taken Plan B and start to experience severe lower abdominal pain three to five weeks after taking it, you should seek medical advice as soon as possible. Having this specific side effect in this timeframe may mean that you have an ectopic pregnancy, which is a pregnancy that happens outside the uterus. Ectopic pregnancies can be life-threatening, which is why it’s so important to talk to a healthcare professional right away if you experience this symptom.

How effective is Plan B?

Plan B is a very effective emergency contraception pill. Plan B works well to prevent pregnancy within three days (72 hours) of an unprotected sex act, but is most effective (>97%) when taken within 24 hours of the incident, says Madeline Sutton, OB/GYN, a medical epidemiologist and former Commissioned Corps Officer at the CDC. A morning-after pill like Plan B can prevent pregnancy 75% to 89% of the time if you take it within three days of unprotected sex.

Even though there’s no limit to how many times you can take Plan B, taking more than one dose per unprotected sex event won’t make it more effective. If you have unprotected sex again the day after taking Plan B, then you should take another dose. Take one pill for every act of unprotected sex, but remember that Plan B is not a substitute for regular birth control. Talk to your healthcare provider about the most appropriate form of birth control for you. 

Is there a Plan B weight limit?

Some research suggests that emergency birth control containing levonorgestrel may be less effective in individuals with a higher BMI. But a 2017 review of four randomized trials found that women with a BMI over 30 had only a slightly higher risk of pregnancy than women overall (2% pregnancy rate versus 1.2% pregnancy rate). These findings suggest that even among women with a higher BMI, Plan B still has a high chance of being effective when used correctly. Still, more research is needed. 

In the United States, there is no weight limit on the Plan B label. The FDA reviewed the efficacy of levonorgestrel in women over 165 lbs or whose BMI was greater than 25, and the labeling remains the same—there are no limitations based on weight. The FDA states that the most important factor is how quickly the medication is taken after unprotected sex or contraceptive failure—as quickly as possible within 72 hours—regardless of the woman’s weight, because it can be highly effective for women of any weight. The FDA also states that all women can use levonorgestrel emergency contraception to prevent unintended pregnancy after contraceptive failure or unprotected intercourse.

However, for women with higher body weights, these two forms of emergency contraception may be more effective:

• Ella (ulipristal acetate): This form of emergency birth control is more effective (in terms of weight) than other morning-after pills in women weighing 165 to 195 lbs. It should be taken within five days (120 hours) of unprotected sex, but the sooner you take it, the better. Women weighing more than 195 lbs should consult their healthcare provider for medical advice. 
• IUDs: Paragard (a copper IUD) or Mirena or Liletta (hormonal IUDs) can be used as emergency contraception—regardless of weight. When put in place within five days of unprotected sex, these IUDs are over 99% effective at preventing pregnancy. Call your healthcare provider as quickly as possible when you realize you need emergency contraception. These IUDs provide emergency contraception (experts say IUDs are the most effective type of emergency contraception available) and also can serve as long-lasting birth control.

Who should not take Plan B?

Even though Plan B is very effective, it isn’t right for everyone and is less effective under the following circumstances:

• Plan B is less effective the longer you wait to take it, so take it as soon as possible.
• It’s not effective if you’re already ovulating or have already ovulated.

If you have a BMI that’s 30 or greater, a copper IUD such as Paragard, hormonal IUD Mirena or Liletta, or the Ella morning-after pill may be better options for you. An IUD is almost 99.9% effective at preventing pregnancy if it is put in within five days after unprotected sex. Once inserted, the Paragard IUD can prevent pregnancy for up to 12 years. Once inserted by a healthcare provider, Mirena can prevent pregnancy for up to 8 years, and Liletta can also prevent pregnancy for up to 8 years.

Ella emergency contraception works to prevent pregnancy up to five days after sex and lowers the risk of pregnancy by about 85%. If you take Ella and need to take another morning-after pill within 5 days, take Ella again (as opposed to Plan B or another morning-after pill). 

Note: Unlike the Plan B pill, the Ella morning-after pill requires a prescription from a healthcare provider to obtain. The Paragard IUD and hormonal IUDs are available by prescription and through your healthcare provider or family planning clinic. You’ll need your OB/GYN to insert the IUD, so if you decide to go that route, call them ASAP and explain the situation so they can bring you in quickly to insert the IUD—it will need to be inserted within 5 days of unprotected sex or contraceptive failure to be effective as emergency contraception. 

Plan B interactions

Certain medications and herbs may decrease the effectiveness of Plan B because they contain enzymes that reduce the concentration of progestins in the blood. Examples of such medicines and herbal products that may interact with Plan B include: 

• Barbiturates such as phenobarbital
• Tracleer (bosentan) 
• Tegretol (carbamazepine) 
• Felbatol (felbamate) 
• Griseofulvin 
• Trileptal (oxcarbazepine)
• Dilantin (phenytoin) 
• Rifampin 
• St. John’s wort 
• Topamax (topiramate)

Plan B does not prevent STDs

Another thing to be aware of is that Plan B doesn’t protect against sexually transmitted infections. The only way to protect yourself from HIV/AIDS, genital herpes, chlamydia, hepatitis, or other STDs is to correctly and consistently use latex condoms or practice abstinence. Some vaccines can prevent hepatitis B and HPV but will not protect against other STDs. The CDC recommends that children get their first dose of the HPV vaccine at age 11 to 12 (but can start as early as age 9 years), but the vaccine is also recommended for everyone up to age 26 (and certain adults ages 27 to 45 years, depending on risk) if they haven’t been vaccinated.

How do you know if Plan B didn’t work?

The only way to know if Plan B has prevented pregnancy is to wait for your next period. If your period arrives more than a week late, that may mean Plan B did not work. However, Plan B may delay menses. Therefore, you may want to consider taking a pregnancy test. 

Some women will experience light bleeding after taking Plan B and may take this as a sign that it’s worked to prevent pregnancy. BUT, spotting is an expected side effect of the morning-after pill and isn’t an indication that it has or has not prevented pregnancy. Getting your period and/or a negative pregnancy test is the only way to know for sure. Consult your healthcare provider with any questions and for medical advice.  

How long is Plan B effective?

It’s best to take Plan B as soon as possible since it works best within the first three days. You can take Plan B up to five days after unprotected sex, but it won’t work as well by the fifth day. It’s best to take it as soon as possible, preferably by the third day after unprotected sex, so it has the best chance of working. 

Once Plan B is ingested, it’s only effective for a maximum of about five days. After this amount of time, the hormones that were in the pill will have left the body. The maximum amount of time that Plan B stays in the body coincides with the amount of time that sperm can live inside the female reproductive tract—about five to six days.

Bottom line—You can still get pregnant after taking Plan B

It’s important to note that you can still get pregnant even after taking Plan B. Also, if you take Plan B after unprotected sex and then have unprotected sex again, you’ll need to take another pill. A long-term form of birth control is the best way to prevent pregnancy. Long-term birth control options include the birth control pill, IUDs, implants, shots, patches, latex condoms, and vaginal rings. For birth control to work, it must be used exactly as directed. If you skip birth control pills, for example, they will not be as effective at preventing pregnancy. And certain forms of birth control, like condoms, must be used every time you have sex to prevent pregnancy. 

Where to buy Plan B 

Anyone can buy Plan B One-Step over the counter at drugstores and pharmacies without a prescription, and regardless of age or gender. You don’t need a prescription for Plan B, and you don’t need to show ID. Some drugstores keep it behind the counter, so you may need to ask the pharmacy staff to get it for you. You can also get it from family planning centers or health department clinics. 

Unfortunately, Plan B can be quite expensive at about $40 to $50. Most insurance companies will cover the cost of Plan B if a healthcare provider prescribes it as an emergency contraceptive. If you’re not able to get a prescription to cover the cost of Plan B, you may be able to get it for free or at a lower price from Planned Parenthood.

Another way to save money on the morning-after pill is SingleCare’s drug coupon. To use the SingleCare discount, you’ll need a prescription from your healthcare provider . These coupons could give you discounts of up to 80% off. SingleCare not only offers discounts on Plan B but other forms of birth control too. Learn how to find free birth control without health insurance here.

Frequently asked questions about Plan B

Is Plan B a morning-after pill?

Plan B is one type of morning-after pill. It is not used for regular birth control. Plan B contains the ingredient levonorgestrel which can prevent pregnancy in the event of unprotected sex or contraceptive failure. To be most effective, Plan B should be taken as soon as possible after unprotected sex or contraceptive failure, preferably within 3 days (72 hours), but can be taken up to 5 days after unprotected sex. The sooner it is taken, the better chance that it will prevent pregnancy. If you are already ovulating, Plan B will not work. 

Can you buy Plan B over-the-counter?

Yes. You can buy morning-after pills like Plan B over the counter at pharmacies. (Ella is the one exception—it’s the only morning-after pill that requires a prescription.) No prescription or identification is required. If you don’t see it on the shelf, you can ask the pharmacist or pharmacy staff, because it may be kept behind the counter. You still won’t need a prescription if it is kept behind the counter. You can also find Plan B at various family planning or health department clinics or Planned Parenthood. You can also check the Plan B website to find locations where you can purchase Plan B. 

What makes Plan B less effective?

Things that make Plan B less effective include:

• Taking it more than 72 hours after unprotected sex or contraceptive failure. It’s best to take Plan B as soon as possible after unprotected sex or contraceptive failure. 
• Taking it with interacting medications. Some medications make Plan B less effective, such as certain seizure medications. See the list above, and consult your healthcare provider if you take any of the medications on the list. 
• Vomiting within 2 hours of taking Plan B can prevent it from working in your body. If you vomit within 2 hours of taking Plan B, consult your healthcare provider right away for medical advice.
• Taking it at certain times of your cycle. Plan B is most effective before ovulation. If you are already ovulating (or have already ovulated), Plan B will not work to prevent ovulation.
• Taking expired medication. It’s a great idea to keep a package or two of Plan B on hand in case of unprotected sex or contraceptive failure so that you can take it as soon as possible when needed. However, check the expiration date. If the medication is expired, it may be less effective, and you should get a new box of Plan B. 

Which is better, Plan B or Ella?

Ella contains the ingredient ulipristal and is considered to be more effective than Plan B and other emergency contraceptives that contain the ingredient levonorgestrel. Ella requires a prescription, while Plan B does not. However, what’s most important is taking emergency contraception as quickly as possible after unprotected sex. So, for example, if it is Friday night and you can’t get in touch with your healthcare provider, it’s best to buy OTC Plan B and take it as soon as possible, rather than wait a few days until you can speak to your healthcare provider to request a prescription for Ella. 

Better yet, plan ahead. Speak to your healthcare provider at your next visit about which would be the best emergency contraception for you. If your healthcare provider thinks Ella would be better, have them call in a prescription to your pharmacy so you can fill it right away and have it on hand. If your healthcare provider thinks Plan B would be better for you, you can pick it up on your next trip to the pharmacy to keep on hand.

Is Plan B an abortion pill?

Plan B is not an abortion pill and will not end a pregnancy if you’re already pregnant. If you’ve accidentally taken Plan B after you’re already pregnant, it’s good to know that there is no evidence to suggest that it’s harmful to developing babies. If Plan B doesn’t work and you become pregnant, it’s unlikely that it will cause harm to you or your baby. Talking with your healthcare provider is the best way to learn about family planning methods that will work best for you.

Will Plan B affect getting pregnant in the future?

You can use Plan B with confidence that it will not affect future fertility. The World Health Organization reports that using hormonal birth control, including emergency contraception like Plan B, does not affect future fertility. These hormones leave the body in several days, and pregnancy can occur from future sexual intercourse.