No, Plan B is not an abortion. Plan B is emergency contraception that prevents pregnancy from happening in the first place. It cannot end an existing pregnancy. This is a common point of confusion, partly because Plan B and the abortion pill are both taken after sex, but they work in completely different ways and at completely different stages.
How Plan B Actually Works
Plan B contains a synthetic hormone called levonorgestrel that stops or delays the release of an egg from the ovary. No egg means no fertilization, which means no pregnancy. It works on the same principle as regular hormonal birth control, just in a higher, single dose taken after unprotected sex.
The FDA reviewed the science and concluded that Plan B works by inhibiting or delaying ovulation and the hormonal changes that trigger it. Older packaging once mentioned possible effects on fertilization or implantation, but the FDA removed that language after determining it wasn’t supported by the best available evidence. The current scientific consensus is that Plan B has no direct effect on fertilization or implantation.
This distinction matters: if you’ve already ovulated and a fertilized egg has implanted in your uterus, Plan B will not work. It does not affect an existing pregnancy in any way.
How the Abortion Pill Differs
Medication abortion uses two different drugs that do something fundamentally different from Plan B. The first drug blocks progesterone receptors, which causes the embryo to detach from the uterine wall and the uterine lining to break down. The second drug, taken a day or two later, causes the uterus to contract and the cervix to soften so the uterus can empty. These drugs end a pregnancy that has already been established.
Plan B prevents a pregnancy from starting. The abortion pill ends one that already exists. As the American College of Obstetricians and Gynecologists puts it: emergency contraception prevents a pregnancy from occurring, while medication abortion ends a pregnancy. They are not interchangeable, and taking Plan B when you are already pregnant will not terminate the pregnancy.
Why the Confusion Exists
Part of the confusion comes from the nickname “morning-after pill,” which makes it sound like something that reverses what already happened. In reality, Plan B is working ahead of your body’s timeline. After unprotected sex, sperm can survive in the reproductive tract for up to five days waiting for an egg. Plan B steps in during that window to prevent the egg from ever being released. It’s contraception, not termination.
The medical community defines the start of pregnancy as the point when a fertilized egg implants in the uterine wall, not the moment of fertilization. Plan B acts well before implantation. Even under definitions that consider fertilization itself to be the start of pregnancy, the FDA’s evidence shows Plan B does not interfere with fertilization either.
How Effective Plan B Is
Timing matters enormously with Plan B. When taken immediately after unprotected sex, it can reduce the risk of pregnancy by roughly 91%. That number drops fast: to about 61% when taken one day later, 28% at two days, and just 19% at three days. The standard recommendation is to take it within 72 hours, but the sooner the better.
Body weight also affects how well Plan B works. Some guidelines suggest that effectiveness begins to decline in people weighing over about 155 pounds (70 kg) or with a BMI above 26. For people with a BMI over 30, a double dose may improve efficacy. Another emergency contraceptive called ella, which works through a different compound, is effective in people weighing up to about 195 pounds. A copper IUD inserted within five days of unprotected sex is the most effective emergency contraception regardless of weight.
What to Expect Afterward
Plan B commonly shifts the timing of your next period. Up to 13% of people experience a delay of more than seven days. Your period might also come earlier than expected, or be heavier or lighter than usual. These changes are temporary. Research shows that menstrual cycle characteristics return largely to normal by the following cycle, and this pattern holds across age groups.
Other common side effects include nausea, fatigue, headache, and lower abdominal pain. These typically resolve within a day or two. If your period is more than a week late after taking Plan B, a pregnancy test is a reasonable next step, since the drug isn’t 100% effective.
The Legal Distinction
Because Plan B is contraception and not abortion, it is not affected by abortion bans. It remains available over the counter in all U.S. states without a prescription or age restriction. The FDA’s position is clear: Plan B does not terminate a pregnancy. This legal and medical classification is based on the drug’s mechanism of action, which prevents ovulation rather than disrupting an established pregnancy.