The recent Supreme Court decision overturning Roe v. Wade, the nearly 50-year-old legal precedent that guaranteed a constitutional right to an abortion, has people scrambling for access to medications that can end a pregnancy or prevent one.

But there is already confusion over the difference between drugs for medication abortion, which are prescribed to end a pregnancy, and emergency contraceptives (including Plan B), which are taken soon after sex and prevent pregnancy.

Medication abortion in the U.S. usually consists of a combination of two drugs, both taken orally after consultation with a medical provider. Approved by the Food and Drug Administration, this protocol includes the drugs mifepristone and misoprostol. They work together by causing something like a heavy menstrual period.

Mifepristone (Mifeprex), also known as RU-486, is taken within 10 weeks of a pregnant person’s last period. It blocks receptors for the hormone progesterone, causing the embryo to detach from the uterine wall and the uterus’s lining to break down, ending the pregnancy. Misoprostol (Cytotec), a synthetic form of a prostaglandin, a group of compounds with hormonelike effects, is taken within a day or two after mifepristone. It causes the uterus to contract and the cervix to soften, allowing the uterus to empty. Misoprostol can be taken on its own to induce an abortion but is more effective when taken with mifepristone.

In contrast, emergency contraception—sometimes called the “morning-after pill”—can be taken up to three to five days after unprotected sex or failed birth control. This kind of drug works primarily by preventing or delaying ovulation, or the release of an egg from an ovary. If ovulation has already occurred, it has been hypothesized that the morning-after pill may prevent the egg from being fertilized or implanting in the uterus, although some studies suggest it does not affect these processes. Importantly, emergency contraception cannot terminate a pregnancy, which the medical community defines as a fertilized egg that has implanted in the uterus.

“The key difference between emergency contraception and medication abortion is that emergency contraception prevents a pregnancy from occurring, while medication abortion ends a pregnancy,” says Jen Villavicencio, lead for equity transformation at the American College of Obstetricians and Gynecologists.

There are several types of morning-after pills: Plan B, perhaps the most well-known, consists of the synthetic hormone levonorgestrel and works by preventing or delaying ovulation. It is available without a prescription and can be taken within 72 hours of sex (the sooner Plan B is taken, the more effective it is). It may not be effective for people heavier than about 155 to 165 pounds, however. “Plan B is not able to induce an abortion,” wrote a spokesperson for Foundation Consumer Healthcare, the company that owns Plan B, in an e-mail to Scientific American.

Another emergency contraceptive called Ella is effective in people who weigh up to about 195 pounds. It contains a drug called ulipristal acetate, and like Plan B, it works by preventing or delaying ovulation. Ella requires a prescription and can be taken within five days of unprotected sex, but it works better the sooner it is taken.

Despite the fact that the morning-after pills do not terminate an existing pregnancy, clinics in some states may falsely interpret abortion restrictions as banning emergency contraceptives, too. Saint Luke’s Health System in Kansas City, Mo., initially stopped providing Plan B at its locations in the state, which has outlawed most abortions, including those resulting from rape or incest. “To ensure we adhere to all state and federal laws—and until the law in this area becomes better defined—Saint Luke’s will not provide emergency contraception at our Missouri-based locations,” said Saint Luke’s Health System spokesperson Laurel Gifford in a statement on June 28, which was reported by the Kansas City Star and other outlets. But the following day the health system said it would resume providing emergency contraception.

Emergency contraception “should never be subject to laws banning abortion,” Villavicencio says. “Any impact of abortion bans on emergency contraception is a misapplication of the law and a misunderstanding of the medical science.”

Contraception—including emergency contraception—remains legal in Missouri and throughout the country. But situations like the one in Kansas City suggest laws restricting abortion could have a chilling effect on access to contraceptives such as Plan B. And it is not a stretch to think the Supreme Court could ultimately roll back protections for contraception in general: in his concurring opinion in the Court’s recent decision in Dobbs v. Jackson Women’s Health Organization, which overturned Roe v. Wade, Justice Clarence Thomas wrote that the court should also reconsider other cases, including Griswold v. Connecticut—a 1965 decision that affirmed married couples’ freedom to buy and use contraception.

For now, it is important for patients and policy makers to know the difference between medication abortion drugs, which are now illegal to prescribe in some states, and emergency contraceptives, which are legal throughout the country.

“Denying people emergency contraception will only leave more people to face the realities of unintended pregnancy without having legal abortion care as a solution,” Villavicencio says.