What Happens If You Don’t Take the Second Abortion Pill?

Taking mifepristone (the first pill) without following it with misoprostol (the second pill) leaves the outcome uncertain. The pregnancy may still end on its own, or it may continue, depending largely on how far along you are. But “nothing happens” is not the right way to think about it. Mifepristone is a powerful drug that starts working immediately, and skipping the second pill introduces risks that the standard two-pill regimen is designed to minimize.

How the Two Pills Work Together

In the standard medication abortion regimen, mifepristone and misoprostol have distinct but complementary jobs. Mifepristone blocks progesterone, the hormone that maintains the uterine lining and supports early pregnancy. Without progesterone signaling, the lining begins to break down and the pregnancy loses its support system. Misoprostol, taken 24 to 48 hours later, causes the uterus to contract and expel the pregnancy tissue. When used together up to 49 days of gestation, the two-drug combination is roughly 95% effective at completing the abortion.¹ A trial comparing different timing intervals found complete abortion rates between 96% and 98% when both pills were used.²

Without that second pill, though, the process is incomplete. Mifepristone has already disrupted the hormonal environment, but the uterus hasn’t received the signal to contract and expel. What happens next is less predictable, and that unpredictability is the core problem.

How Often the Pregnancy Continues Without the Second Pill

Mifepristone alone ends the pregnancy more often than you might expect, but far less reliably than the full regimen. Data from a systematic review on mifepristone-only outcomes found that at seven weeks of gestation or earlier, roughly 22% of pregnancies continued after mifepristone alone. At seven to eight weeks, that number jumped to about 50%.³ In other words, even without the second pill, the majority of very early pregnancies end after mifepristone. But the further along the pregnancy, the more likely it is to survive mifepristone on its own. By eight weeks, it becomes essentially a coin flip.

A separate systematic review confirmed that when women take mifepristone and then do not take misoprostol, it is possible for the pregnancy to continue to a live birth.⁴ So the short answer is: skipping the second pill does not guarantee the pregnancy ends, and at later gestational ages, continuation becomes increasingly likely.

The Hemorrhage Risk

This is where the safety picture gets concerning. A randomized trial designed to test whether progesterone could counteract mifepristone had to be stopped early after enrolling only 12 patients because of severe bleeding events. Three participants experienced hemorrhage serious enough to require ambulance transport to a hospital. One of those patients needed a blood transfusion. The researchers concluded that patients in early pregnancy who use only mifepristone, without subsequent misoprostol, may be at high risk of significant hemorrhage.⁵

The reason relates to what mifepristone does to the uterine lining. By blocking progesterone, mifepristone destabilizes the lining, which can lead to unpredictable, heavy bleeding even without the contractions that misoprostol would normally trigger. When misoprostol is used as intended, it helps the uterus contract and expel tissue in a more controlled way. Without it, the tissue breakdown happens on a less predictable timeline, and the risk of sudden, heavy blood loss goes up.

A larger retrospective study found that emergency department visits were relatively uncommon overall but did occur. About 2.7% of cases involved an ED visit, and hospitalizations were rare at around 0.5%. No maternal deaths were recorded in that dataset, and no cases required antibiotics or blood transfusion in the broader cohort.⁶ So life-threatening complications are uncommon, but serious bleeding episodes do occur and are a real reason this situation needs medical attention rather than a wait-and-see approach at home.

What Incomplete Abortion Looks Like

If the pregnancy does not end completely after mifepristone alone, you may experience what clinicians call an incomplete abortion. This means that some pregnancy tissue has been expelled but some remains in the uterus. Symptoms can include prolonged or heavy bleeding, cramping that doesn’t resolve, and sometimes fever or signs of infection if tissue is retained for too long. Retained tissue can also lead to sepsis in rare cases, which is a medical emergency.

The tricky part is that some bleeding and cramping are normal even after mifepristone alone, so it can be difficult to tell on your own whether the process has completed. An ultrasound or blood test checking pregnancy hormone levels is the reliable way to determine what has happened. If you’ve taken mifepristone and decided not to take misoprostol, or if you’re unsure what to do next, contacting a healthcare provider is important regardless of what you ultimately decide about the pregnancy. The concern is not just whether the pregnancy ends or continues, but whether retained tissue creates a medical problem in the meantime.

If the Pregnancy Continues After Mifepristone Exposure

For someone who takes mifepristone but then decides to continue the pregnancy, the question of whether the drug harms the developing fetus becomes central. The evidence here is mixed, and researchers have gone back and forth on how to interpret the available data.

A systematic review looking specifically at whether mifepristone causes birth defects concluded that the drug does not appear to be a teratogen based on available human data. Congenital anomalies did show up in some cases, but the review noted that many were explained by factors other than the drug itself.⁴ A prospective observational study found the rate of major congenital malformations after first-trimester mifepristone exposure was about 4%, compared with the expected 2% to 3% rate in the general population. The authors described this finding as “reassuring.”⁷

But a more recent meta-analysis struck a more cautious tone. While the overall malformation rate was not dramatically elevated, the analysis found that exposure to mifepristone and/or misoprostol was linked to higher odds of specific rare conditions: hydrocephalus, Möbius syndrome (a condition affecting cranial nerves that control facial expression and eye movement), and terminal transverse limb defects (where parts of a limb fail to fully develop). The odds ratios for these specific conditions were substantially elevated.⁸ Möbius syndrome in particular has been linked to misoprostol exposure specifically.⁹

An important distinction here: if you took only mifepristone and not misoprostol, the misoprostol-associated risks (especially Möbius syndrome and limb defects) would not apply, since those are primarily tied to the second drug. The mifepristone-specific risk appears smaller, but the honest answer is that the data is thin. These are rare conditions, the studies are small, and it’s hard to draw firm conclusions. If you’re in this situation, the conversation with your provider should include what the specific exposure was, how far along the pregnancy is, and what monitoring makes sense going forward.

The “Abortion Pill Reversal” Debate

You may have encountered claims that a medication abortion can be “reversed” by taking progesterone after mifepristone. This idea has become deeply entangled with politics, and the science is genuinely difficult to separate from the advocacy on both sides.

The concept behind reversal is straightforward in theory: since mifepristone blocks progesterone receptors, flooding the body with extra progesterone might outcompete mifepristone at those receptors and allow the pregnancy to continue. A case series reported that intramuscular progesterone and high-dose oral progesterone achieved continuation rates of about 64% and 68%, respectively.¹⁰ A small pilot trial in Australia prescribed oral progesterone at 400 mg twice daily for three days, then 400 mg nightly for the remainder of a 19-day course.¹¹

But there’s a significant problem with interpreting these numbers. Remember that mifepristone alone results in ongoing pregnancies about 22% to 50% of the time depending on gestational age. A systematic review comparing progesterone-treated patients with mifepristone-only controls found that the ongoing pregnancy rate for those who received progesterone was not significantly higher than for those who received mifepristone alone.³ In other words, when you account for the baseline rate of pregnancy continuation after mifepristone alone, progesterone may not be adding much. The data quality was also rated as poor.

The only randomized controlled trial attempting to properly test this question was the one halted for safety after three hemorrhage events among just 12 participants. Among the 10 who completed enough of the trial to be evaluated, fetal cardiac activity continued in four out of five progesterone patients versus two out of five placebo patients, but the numbers are too small to mean much statistically.⁵ The researchers themselves said they could not estimate efficacy. Mainstream medical organizations have pointed out that the evidence base for “abortion pill reversal” is made up of case series and uncontrolled data, which is the weakest form of clinical evidence.¹²

State Laws Requiring Reversal Counseling

Despite the thin evidence, the concept of abortion pill reversal has moved into law in multiple states. As of 2021, 14 states had enacted laws related to medication abortion reversal, mostly in the Midwest and South. These laws generally require that patients receive information about reversal during pre-abortion counseling, instruct them to contact a healthcare provider or visit specific reversal-related resources, and in some cases require reversal information to be posted on state-managed websites.¹³

The practical result is confusing for patients. If you live in one of these states and you’ve taken the first pill, you may be told that reversal is a proven option when the scientific consensus is that it remains unproven. A provider in a different state might give you very different information. This doesn’t mean that continuing a pregnancy after mifepristone is impossible; it clearly happens on its own a meaningful percentage of the time. It means the specific claim that progesterone treatment reliably improves your chances of continuation, above and beyond what would happen anyway, is not well supported.

Practical Considerations if You’re in This Situation

If you’ve taken mifepristone and are reconsidering the second pill, or if circumstances prevented you from taking it, a few things are worth knowing. First, time matters. The longer you wait after mifepristone, the more uncertain the outcome becomes. Mifepristone has a half-life of about 25 to 30 hours, meaning its activity diminishes over the following days, but its effects on the uterine lining may already be underway.

Second, doing nothing and hoping for the best carries real risks. Whether the pregnancy continues or not, you need medical follow-up. An incomplete process can lead to retained tissue, infection, or unpredictable bleeding. If you want the abortion to proceed, your provider can prescribe misoprostol or schedule a procedural abortion. If you want the pregnancy to continue, your provider can assess viability through ultrasound and monitor for complications.

Third, if you are experiencing heavy bleeding, soaking through more than two thick pads per hour for two or more hours, feeling dizzy or faint, or running a fever, seek emergency care. These signs can indicate hemorrhage or infection and should not wait for a scheduled appointment.

Why the Evidence Is So Limited

One reason definitive answers are hard to come by is that studying this scenario is ethically complicated. You cannot randomly assign people to “skip the second pill” in a controlled trial. Most of what we know comes from case series, observational data, and the handful of studies designed to test reversal that were either halted or underpowered. The systematic reviews do their best with the data available, but they consistently note that the quality of evidence is low.

The halted randomized trial is particularly telling. It was designed to answer the exact question many people have, whether progesterone after mifepristone can maintain a pregnancy, and it had to stop because participants were getting hurt. That makes it very unlikely a similar trial will be attempted anytime soon, which means the debate over reversal will continue to rely on imperfect data for the foreseeable future. For the related question of fetal safety after mifepristone exposure, the picture is somewhat more reassuring. The overall malformation rate does not appear dramatically elevated, though the possibility of increased risk for specific rare conditions means that any pregnancy continuing after mifepristone exposure warrants careful prenatal monitoring.

Emergency Room Visits After Medical Abortion

A large longitudinal study tracking emergency room use between 1999 and 2015 found that all types of ER visits were more likely to occur after medical (pill-based) abortion than after surgical abortion. Abortion-related ER visits were about one and a half times as likely after medical abortion, and visits coded as spontaneous abortion were roughly twice as likely.¹⁴ These numbers reflect the standard two-pill regimen, not specifically the scenario of skipping the second pill, but they give context for the kind of complications that can arise during medical abortion in general. Incomplete abortion, heavy bleeding, and infection are the most common reasons patients seek emergency care, and all three risks are at least as high, and likely higher, when the regimen is not completed as prescribed.