The first abortion pill, called mifepristone, blocks the hormone progesterone. Progesterone is what keeps the uterine lining thick and nourishing so a pregnancy can stay attached. Without it, the lining thins and the pregnancy detaches from the uterine wall. This single 200 mg pill is the first step in a two-medication process approved for ending a pregnancy through 10 weeks of gestation (70 days from the first day of your last period).
How Mifepristone Works in the Body
Progesterone is essential for maintaining a pregnancy from its earliest stages. It keeps the uterine lining rich with blood vessels and nutrients, creating the environment the embryo needs to develop. Mifepristone binds to progesterone receptors more tightly than progesterone itself does. Lab studies show mifepristone’s binding affinity for these receptors is more than double that of progesterone, meaning it effectively locks progesterone out.
Once mifepristone occupies those receptors, progesterone can no longer signal the uterus to maintain its lining. The lining begins to break down, and the pregnancy loses its attachment. Mifepristone also softens the cervix slightly, which prepares the body for what happens next when the second medication is taken.
What You Actually Feel After Taking It
Most people feel little to nothing after taking the first pill. Some experience mild nausea or light spotting, but the significant physical effects don’t begin until the second medication, misoprostol, is taken 24 to 48 hours later. Misoprostol causes the uterus to contract and expel its contents, which is when cramping and bleeding occur. The first pill is doing its work quietly, changing the hormonal environment inside the uterus without producing dramatic symptoms.
The Two-Pill Process
Mifepristone is always the first step. You take one 200 mg tablet by mouth. Then, 24 to 48 hours later, you take misoprostol, which triggers uterine contractions. The two medications work as a pair: mifepristone detaches the pregnancy, and misoprostol clears it from the uterus. Without both steps, the process is less effective.
The entire process can be done at home as long as you have access to a healthcare professional by phone or online. Bleeding and cramping typically begin within a few hours of taking the second pill and can last several hours, though the heaviest part usually passes within the first day.
Who Should Not Take Mifepristone
Mifepristone is not safe or effective for everyone. It will not work for an ectopic pregnancy (a pregnancy growing outside the uterus), and taking it in that situation is dangerous because the ectopic pregnancy would continue unaddressed. Other situations where mifepristone is not used include:
- Bleeding disorders or blood-thinning medications, because of the risk of heavy bleeding
- Chronic adrenal insufficiency or long-term corticosteroid use, because mifepristone also interacts with cortisol receptors and could disrupt adrenal function
- An IUD still in place, which can interfere with the process (though it can be removed first)
- A known allergy to mifepristone or misoprostol
- Inherited porphyrias, a group of rare metabolic conditions that mifepristone can worsen
Effect on Future Fertility
Taking mifepristone as part of a medication abortion does not appear to raise the risk of complications in future pregnancies. Research reviewed by the Mayo Clinic found no increased risk of fertility problems, preterm birth, or other pregnancy complications after a medical abortion. The uterine lining rebuilds during the next menstrual cycle, and ovulation can return within a few weeks, meaning pregnancy is possible again relatively quickly.
How It Differs From the Second Pill
People often conflate the two pills, but they do very different things. Mifepristone is a hormone blocker. It changes the chemical conditions inside the uterus so the pregnancy can no longer be sustained. It works over hours, gradually thinning the lining, and you’re unlikely to notice it happening. Misoprostol, by contrast, is the medication that causes physical contractions. It’s the pill responsible for cramping, heavy bleeding, and the passage of tissue. Think of mifepristone as loosening the foundation and misoprostol as clearing the structure.
Because mifepristone works silently, some people wonder whether it actually did anything. The lack of immediate symptoms is normal and expected. Its job is hormonal, not mechanical, and the visible evidence of its effect only becomes apparent once the second pill triggers contractions.