The abortion pill is actually two medications taken in sequence, and each one affects the pregnancy differently. The first pill cuts off the hormonal support that maintains the pregnancy, while the second triggers the uterus to expel its contents. At the gestational ages when medication abortion is used (up to 10 or 11 weeks), the embryo or early fetus is typically smaller than a thumb, and its nervous system is far too undeveloped to process pain.
How the First Pill Works
The first medication, mifepristone, blocks progesterone, the hormone that sustains pregnancy. Progesterone keeps the uterine lining thick and blood-rich so it can nourish the developing embryo. When mifepristone binds to progesterone receptors in the uterine lining, it effectively locks progesterone out.
Without progesterone doing its job, the uterine lining begins to break down. Research on tissue samples from women within 39 to 49 days of gestation shows that within 48 hours of taking mifepristone, the uterine lining and the finger-like projections that connect the embryo to the blood supply (called chorionic villi) show signs of degeneration. The blood supply to the embryo becomes insufficient. Cells in both the uterine lining and the early placental tissue undergo programmed cell death at significantly higher rates than normal. This process stops the pregnancy from being able to sustain itself, even before the second pill is taken.
If someone takes only the first pill and not the second, the pregnancy does not always end. Studies show that anywhere from 8% to 46% of pregnancies may continue one to two weeks after mifepristone alone, depending on the dose and gestational age. This is why the second medication is a critical part of the process.
How the Second Pill Works
The second medication, misoprostol, is taken 24 to 48 hours after the first. It does something completely different: it softens and opens the cervix while triggering strong uterine contractions. These contractions are similar to what happens during a miscarriage. They physically expel the pregnancy tissue, including the embryo, the gestational sac, and the broken-down uterine lining.
Cramping and bleeding typically begin one to four hours after taking misoprostol. The heaviest part of the process usually lasts two to six hours, though it can take longer. The bleeding is heavier than a normal period and involves passing clots and tissue. For most people, the worst of it is over within a day, though lighter bleeding can continue for days or weeks afterward.
What the Embryo Looks Like at This Stage
Medication abortion is used during the first trimester, most commonly before 10 weeks. At this stage, what’s expelled looks quite different from what many people picture. At six weeks, the embryo is roughly the size of a pomegranate seed, enclosed within a small gestational sac and surrounded by amniotic membranes and a yolk sac. The entire structure, including the sac, is about 1 centimeter across. At eight or nine weeks, the embryo is closer to the size of a grape. Many people who go through a medication abortion report that it’s difficult to distinguish the embryo from the surrounding blood clots and tissue.
By 10 to 11 weeks, the developing fetus is slightly larger, roughly the size of a strawberry, and basic features like limb buds are forming. But it is still very small, and the tissue passed during the abortion is a mix of blood, clots, the gestational sac, and the uterine lining.
Whether the Embryo Can Feel Pain
This is one of the most common concerns people have. The scientific consensus is clear: an embryo or fetus cannot feel pain during the window when medication abortion takes place. The American College of Obstetricians and Gynecologists states that the neural circuitry needed to distinguish touch from painful touch does not develop until late in the third trimester. The Royal College of Obstetricians and Gynaecologists reached the same conclusion after reviewing over 50 studies, finding that fetal pain is not possible before 24 weeks of gestation.
Pain is not just a nerve signal traveling to the brain. It requires conscious recognition of a harmful stimulus, which depends on brain structures and neural connections that simply don’t exist in the first trimester. While an embryo may show reflexive movements, these are automatic responses that do not involve awareness or suffering, much like a knee-jerk reflex. Even during fetal surgery later in pregnancy, anesthesia is used to prevent movement and stress responses rather than because the fetus is thought to consciously experience pain at those stages.
What Happens Biologically, Step by Step
Putting the full sequence together: after the first pill, progesterone is blocked and the uterine lining starts deteriorating. Blood flow to the embryo decreases as the tissue connecting it to the uterine wall breaks down. Cellular death accelerates in both the lining and the early placental structures. The embryo, dependent entirely on this blood supply for oxygen and nutrients, stops developing.
When the second pill is taken a day or two later, contractions begin. The cervix softens and opens. The uterus pushes out the pregnancy tissue in a process that feels like intense period cramps. The embryo, already no longer viable from the effects of the first pill, is expelled along with the gestational sac and uterine lining.
How Effective the Process Is
Medication abortion is highly effective when both pills are taken as directed. At seven weeks of gestation, the success rate is about 98.5% for completing the abortion without needing any additional intervention. Effectiveness is highest earlier in pregnancy and decreases slightly at later gestational ages. In the small percentage of cases where the medication does not fully complete the process, a follow-up procedure or additional doses may be needed.