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

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

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 Plan B works

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 or prevent a fertilized egg from attaching to the uterus. Plan B works if taken within 72 hours after a regular birth control method fails or within 72 hours after unprotected intercourse.   

Once absorbed 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 and fights your body’s natural functions, it can often cause side effects. Here are some of the most common side effects that women experience:   

  • Nausea
  • Lower abdominal pain
  • Breast tenderness 
  • Fatigue
  • Spotting/changes in menstrual bleeding
  • 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. It works well to prevent pregnancy within three days 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 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. 

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:

  • It’s 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.

If you have a BMI that’s 30 or greater, a copper IUD or the Ella morning-after pill may be better options for you. The Paragard (copper) IUD is almost 99.9% effective at preventing pregnancy if it is put in within five days after unprotected sex, and once inserted, can prevent pregnancy for up to 12 years. 

Ella emergency contraception works to prevent pregnancy up to five days after sex and lowers the risk of pregnancy by about 85%. However, you should not take Plan B or other morning-after pills containing levonorgestrel if you have taken Ella since your last period. 

Note: Unlike the Plan B pill, the Ella morning-after pill requires a prescription from a doctor to obtain. The Paragard IUD is available by prescription and through your doctor or family planning clinic. You’ll need your OB-GYN to insert the IUD, so if you decide to go that route, call the office as soon as possible and explain the situation so they can bring you in quickly to insert the IUD.

Plan B interactions

Certain medications and herbs may also 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 include:  

  • Barbiturates
  • Bosentan  
  • Carbamazepine  
  • Felbamate  
  • Griseofulvin  
  • Oxcarbazepine  
  • Phenytoin  
  • Rifampin  
  • St. John’s wort  
  • 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 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.   

RELATED: Should you get the hepatitis B vaccine?

How do you know if Plan B worked?

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, 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. However, 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. 

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 it 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. 

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 it up to five days after unprotected sex, but it won’t work as well by the fifth day. Once 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 it 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 (if used every time you have sex).

Where to buy Plan B 

Adults can buy Plan B One-Step over-the-counter without a prescription at most drugstores and pharmacies. You can also get it from family planning centers or health department clinics. 

Unfortunately, Plan B can be quite expensive at about $38 to $58 per pill. Most insurance companies will cover the cost if a healthcare provider prescribes it as an emergency contraceptive. If you’re not able to get a prescription, 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. These coupons could give you discounts of up to 80% off, but you will need to seek a prescription from your provider first. SingleCare offers discounts on other forms of birth control, too. Learn how to find free birth control without health insurance here.