'Why not Plan B?': Here's what you're getting wrong about the emergency birth control

"Just take Plan B."

With the overturn of Roe v. Wade, some Americans are scrambling to find safe and effective ways to prevent unwanted pregnancies, one of them being emergency contraception medications.

For many, Plan B has been hailed as a miracle, morning-after pill. It can be up to 95% effective in preventing pregnancy if taken immediately after unprotected sex and is available without a prescription. But contrary to what you may have heard, the pill does not work for everyone.

Sexual health experts warn it's not a replacement for the abortion pill. Plan B has no impact on existing pregnancies and may not be accessible, affordable, or effective for everyone – depending on body weight and menstrual cycle.

"One of the things that prevents people from even using Plan B or knowing about it is that it's confusing," says Cynthia Harper, a professor at the University of California, San Francisco's Department of Obstetrics Gynecology and Reproductive Sciences.

"It's a sensitive topic and the more that people read about it and understand the benefits and shortcomings… then they'll be much better equipped to take care of themselves in this new context that we're in."

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What is Plan B and how does it work?

Plan B is a form of emergency birth control that should be taken within 72 hours after unprotected sex. It is typically sold for $50 at drug stores such as CVS and Rite Aid, and there is no age requirement to purchase.

The one-pill dose works by delaying ovulation with a hormone called levonorgestrel. According to Planned Parenthood, it can lower your chance of getting pregnant "by 75% to 89% if you take it within three days after unprotected sex."

But as the name suggests, Plan B is recommended as a backup, not primary, method of birth control.

"Plan B is not a birth control method. It's an emergency contraceptive method," says Michelle Hope, a sexologist and reproductive justice activist. "It should not be used regularly because that is not how it was designed. Plan B works like a birth control pill but has a much higher dosage of hormones … so it can disrupt regular levels of hormones in your body."

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Plan B isn't effective for everyone. Who doesn't it work for? 

Timing is key: Because Plan B prevents ovulation, it won't work for those who are already ovulating. Harper explains this is because the egg cannot be stopped from being fertilized by sperm once released from the ovary.

In addition, certain medications and supplements can impact the efficacy of Plan B, such as the herb St. John's wort or certain seizure medications. And research has supported that the pill may fail those with higher body weights. Some studies, such as a 2011 study published in the journal Contraception, found it was less effective for people weighing over 170 pounds. Organizations like Planned Parenthood advise against using Plan B if you have a body mass index (BMI) of 30 or more.

The exact science surrounding the relationship between Plan B and weight is unclear. But Katharine White, associate professor of OB-GYN at the Boston University School of Medicine and author of "Your Sexual Health," says it may be because of the body weight's impact on the metabolism and distribution of levonorgestrel.

"When the medication gets distributed over a larger body weight, there may be less hormone in the blood to tell the brain to tell the ovary not to ovulate, since the hormone gets diluted," White explains.

Can you take multiple Plan B pills for safe measure?

Experts say there is no limit to the number of times a person can take Plan B. However, an Oregon Health Sciences University study found that doubling the dose of Plan B does not prevent ovulation any more than a single dose.

Rather than taking Plan B regularly – which could cause irregular bleeding or spotting – health experts recommend other birth control options such as the copper IUD or the lesser-known and prescription-only emergency contraceptive, the Ella pill, for those weighing between 155 and 195 pounds.

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What will happen to Plan B now?

Since the fall of Roe, concerns have arisen concerning the future of birth control and Plan B. Already, pharmacy chains like Rite-Aid and CVS have set purchase limits due to overwhelming demand, and some states have adopted restrictions on emergency contraceptives, according to the Guttmacher Institute, with some excluding it from contraceptive coverage mandates and others allowing pharmacists to refuse its dispersal.

"Not everyone is aware of Plan B. You have to know where to get it and if it's available – and not all pharmacies stock it. Not all pharmacists will decide to give it, especially in a state with restrictions on parental consent for adolescents in birth control," White says.

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Harper adds that even though Plan B doesn't require a prescription like most birth control methods, it's still inaccessible for many, particularly for low-income and marginalized youth. One important way to increase equitable access is to encourage accurate contraceptive awareness through inclusive sex education. 

"We cannot separate the idea of the removal of reproductive rights from the limitations we're seeing in sex education across the nation," Hope says. "Sex education is the best way for us to educate young people, marginalized groups who are at the greatest risk, on how to protect themselves and make decisions that are best for their bodies, their reproductive health, their relationships and their sexual health."

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This article originally appeared on USA TODAY: Plan B is not an alternative to abortion. Here's why