If you're reading this, you may feel like you need a plan B to prevent an unwanted pregnancy. Whether your birth control failed or you didn't use a birth control method, the Plan B One-Step® emergency contraceptive pill, AKA the morning-after pill, can be an effective way to prevent an unwanted pregnancy in the few days following unprotected sex.
But you also may be concerned about what side effects or disadvantages are involved in taking this emergency contraception pill.
What are the main Plan B emergency contraception side effects?
Side effects are an unfortunate part of taking medication, and Plan B side effects are no different. Some things you may experience include:
Changes in menstrual bleeding
How long do you have to take Plan B?
Plan B One-Step is the most common brand name for the levonorgestrel 1.5mg tablet. It is an emergency contraceptive pill taken by mouth once as soon as possible after unprotected sex—the sooner you take it, the more effective it will be (preferably within 12 hours of having unprotected sex).
However, Plan B can prevent pregnancy if taken within 72 hours. If you take it within 24 hours of unprotected sex, it'll be 95% effective.
It’s easy to purchase Plan B online or at drugstores without a prescription. Planned Parenthood family planning clinics also offer access. Additionally, if you're a member of an online birth control telemedicine service like ours, you can get Plan B along with a birth control pill prescription.
What is Plan B One-Step and how does it work?
What exactly happens to your body when you take Plan B? The active ingredient in the pill is called levonorgestrel. It's similar to the hormone progesterone that occurs naturally in your body.
Ovulation is when an egg is released from a female's ovary and can be fertilized by male sperm for a potential pregnancy. But when you take Plan B, ovulation can be prevented, and an egg won't be released. Even if sperm are present, they won't be able to fertilize an egg, stopping pregnancy from occurring.
Plan B also may work by thickening the fluid on your cervix, which separates your vagina from your uterus. This makes it difficult for sperm to move into the correct position to produce a fertilized egg and a pregnancy.
Everything you need to know about Plan B side effects
The active ingredient in Plan B, levonorgestrel, is the same ingredient used in many birth control pills, but at a higher dose. This means many potential side effects are similar to those of birth control pills that contain any type of progestin hormone, also known as combined oral contraceptives.
Common side effects (occurring in >10% of women and people who menstruate in clinical trials):
Heavier menstrual bleeding: This is the most commonly experienced side effect and most likely due to levonorgestrel's effect on your uterine lining. The shedding of this uterine lining is what causes normal bleeding during your menstrual period. The FDA reports occurrence in up to 31% of women and people who menstruate.
Nausea/lower abdominal pain: Gastrointestinal issues like nausea or abdominal pain are common with hormonal change, and taking a high dose of levonorgestrel certainly counts as a hormonal change. The FDA reports these side effects in about 13% of women and people who menstruate. If you do vomit within two hours of taking Plan B, you will most likely need to retake the pill, but you can call your healthcare provider or pharmacy to check if you are unsure.
Fatigue: Levonorgestrel has similar effects as the human hormone progesterone. When this hormone is at high levels, it can make you feel less energetic than you may be normally. Fatigue affects about 13% of people that take Plan B.
Headache: Hormones that regulate our menstrual cycle and pregnancy can also affect headache chemicals in the brain. About 10% of women and people who menstruate experience headaches after taking Plan B.
Rare side effects (occurring in <4% of women and people who menstruate in clinical trials):
Dizziness: About 10% of people report some dizziness while on Plan B.
Breast tenderness: Another effect of multi-tasking hormones is they can cause your breasts to swell a bit, potentially causing tenderness. About 8% of women and people who menstruate have this.
Delayed period: You might experience menstrual changes, which can come early or late due to cycle interruptions from taking a high dose of levonorgestrel. We've covered this in more detail here. If your period is more than 5 days late, it's a good idea to take a pregnancy test or contact your healthcare professional. Most of the time your next period will be normal after taking Plan B.
How Long do Plan B Side Effects Last?
Most of these side effects, if you have any, will begin within a couple hours to a day of taking Plan B and will only last about two or three days.
Some women and people who menstruate are concerned about the long-term effects of Plan B on fertility, or their ability to eventually get pregnant if they want to. It can be tough to accurately measure the long-term effects of Plan B use on fertility, because many different factors affect fertility, such as age and the health of your eggs.
That said, it's important to keep in mind that Plan B is meant for emergency contraception and should not be used as your regular form of birth control. If you are having sex regularly, there are many birth control options available to prevent pregnancy. Read about just a few options here and here.
If you're breastfeeding, you can take Plan B, but small amounts of progestins do pass into breast milk, shown as detectable levels in infants. However, this has not been found to impact the health, growth or development of the infant.
How to take Plan B
As soon as possible after you have unprotected intercourse (ideally within 24 hours), swallow the one pill that comes in the Plan B package. The cost of the brand name Plan B One Step pill is around $50. Other brands are available for much less, around $15 to $30. With health insurance, the cost of generic Plan B could be as low as $0. The Pill club members can get generic Plan B online and delivered for free.
If you take Plan B within 72 hours after unprotected sex, your chance of becoming pregnant is low, but not impossible. The only way to know for sure whether you're pregnant is to take a pregnancy test.
If your next period does not come within a week of when you expect it, it's a good idea to take a pregnancy test and seek medical advice from your OB/GYN or healthcare provider.
Keep in mind that no pills, IUDs, rings, implants or shots used for birth control also protect against sexually transmitted infections (STIs). Using a condom is always a good idea unless you and your partner only have sex with each other and have both been checked for STIs.
Takeaways
The most common side effects of the Plan B pill are relatively mild and do not last very long. Plan B is a very effective option for occasional instances where your regular birth control method fails. Your chance of avoiding an unwanted pregnancy is high as long as you take Plan B within 72 hours of unprotected sex, or even better, within 24 hours.
While Plan B has the potential to cause some unpleasant side effects, some women and people who menstruate find that its benefits in preventing an unwanted pregnancy allow them to take ownership of their sexual health, while outweighing the risks of experiencing side effects.
Hormone Headaches. National Health Service UK. Page reviewed June 11 2018. Accessed July 15 2021.
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