The pill used to induce labor is misoprostol, sold under the brand name Cytotec. It works by softening the cervix and triggering contractions, and it’s one of the most widely used methods of labor induction worldwide. Despite its widespread use in obstetrics, misoprostol was originally developed to treat stomach ulcers and has never been formally approved by the FDA for labor induction, making its use in pregnancy technically “off-label.”
How Misoprostol Works
Misoprostol is a synthetic version of a natural hormone-like substance called prostaglandin E1. Your body already produces prostaglandins near the end of pregnancy to prepare for labor, and misoprostol essentially amplifies that process. It does two things simultaneously: it breaks down the tough, fibrous tissue in the cervix so it softens and opens, and it stimulates the muscular wall of the uterus to begin contracting. The strength of the contractions increases in a dose-dependent way, meaning higher doses produce stronger, more frequent contractions.
This is different from the other common prostaglandin medication used for induction, dinoprostone (a prostaglandin E2 product), which works more on the cervix itself. Dinoprostone triggers an inflammatory process that remodels cervical tissue and helps the body withdraw from progesterone, the hormone that keeps the uterus quiet during pregnancy. Misoprostol acts more directly on the uterine muscle, which is why it tends to produce faster results but also carries a higher risk of overly frequent contractions.
How the Pill Is Given
Misoprostol can be given by mouth or placed vaginally, and the route matters. When swallowed, the pill is absorbed quickly, reaching peak levels in the blood within about 30 minutes, but it’s also cleared from the body fast, within two to three hours. When placed vaginally, absorption is slower (peaking around one hour) but the medication stays active longer, four hours or more. That sustained exposure translates to meaningful clinical differences.
In studies comparing the two routes, vaginal misoprostol produced significantly faster results. The average time from induction to delivery was about 10 hours with vaginal placement versus roughly 16.5 hours when taken by mouth. About 90% of women given the vaginal dose delivered within 24 hours, compared to around 73% with oral dosing. Vaginal placement also required fewer doses overall, with about 40% of women needing only two doses to achieve delivery.
The trade-off is that vaginal misoprostol roughly triples the rate of tachysystole, a pattern of overly frequent contractions (about 27% versus 10% with oral dosing). Because of this, many hospitals now favor oral misoprostol at lower starting doses to balance effectiveness with safety. A common approach is to start with a small dose of 25 micrograms by mouth every two hours, though some protocols begin at 50 micrograms and increase to 100 micrograms every four hours depending on how the body responds.
How Long Induction Takes
When compared head-to-head with dinoprostone (the other prostaglandin commonly used for induction), misoprostol consistently gets things moving faster. In one large comparison, women given misoprostol delivered in an average of about 12 hours, while those given dinoprostone took closer to 15.5 hours. Nearly 58% of women on misoprostol delivered within 12 hours, compared to about 33% on dinoprostone. By the 24-hour mark, almost 99% of the misoprostol group had delivered.
Misoprostol also required fewer repeat doses. Only about 8% of women in the misoprostol group needed a second or third dose, compared to 22% with dinoprostone. These numbers help explain why misoprostol has become a preferred option in many hospitals: it works faster, requires fewer doses, and achieves vaginal delivery more reliably.
That said, every induction is different. The state of your cervix at the start, whether this is your first baby, how far along you are, and your individual biology all influence how quickly things progress. Some women begin active labor within a few hours of the first dose. Others need a full day or longer.
What to Expect During the Process
After receiving misoprostol, you’ll typically be monitored for about an hour so the care team can track the baby’s heart rate and watch for any signs of excessive contractions. If the oral route is used, doses are spaced two to four hours apart, and you may have periods between doses where monitoring is less intensive. If contractions don’t begin or the cervix isn’t responding, additional doses are given until labor is established or a daily maximum is reached.
The experience often starts slowly. Early contractions may feel like period cramps and gradually build in intensity. Some women describe a long stretch of mild, irregular tightening before things shift into active labor. Others find that contractions ramp up quickly after the first or second dose. Pain management options, including epidurals, are available once labor is active, and receiving misoprostol doesn’t limit your choices in that regard.
Risks and Side Effects
The primary concern with misoprostol is uterine tachysystole, defined as six or more contractions within a 10-minute window. This pattern of overly frequent contractions can reduce blood flow to the baby between contractions, leading to drops in the fetal heart rate. Research published in the American Journal of Obstetrics and Gynecology found that tachysystole within the first four hours of induction was significantly associated with fetal heart rate decelerations. This is why continuous monitoring is standard practice after each dose.
Other side effects can include nausea, diarrhea, and fever, which reflect the drug’s original design as a stomach medication. These tend to be mild and short-lived. The cesarean delivery rate with oral misoprostol is slightly higher than with vaginal placement (roughly 25% versus 10% in one study), largely because oral dosing is less reliably effective and more women end up needing surgical delivery when labor stalls.
Who Should Not Receive Misoprostol
The most important contraindication is a previous cesarean section or any other surgery that left a scar on the uterus. Misoprostol’s strong effect on uterine contractions significantly increases the risk of uterine rupture, where the scar tears open during labor. This risk was identified in studies conducted between 1998 and 2001, and by 2002 the American College of Obstetricians and Gynecologists declared misoprostol contraindicated for women with a prior cesarean. Every major international guideline has since agreed. For women who’ve had a previous cesarean and need induction, other methods are used instead.
Women with certain allergies to prostaglandins, active genital herpes outbreaks, or placenta previa (where the placenta covers the cervix) are also typically not candidates for misoprostol induction.
Why an Unapproved Drug Is Standard Practice
It may seem strange that the most commonly used pill for labor induction was never approved for that purpose. Misoprostol received FDA approval in 1988 solely for preventing stomach ulcers caused by anti-inflammatory drugs. Obstetricians began using it for labor induction in the 1990s after research showed it was effective, inexpensive, and easy to store (unlike dinoprostone, which requires refrigeration). In 2000, the manufacturer issued a warning against its use in pregnancy, citing reports of maternal and fetal deaths, which intensified public debate. However, medical organizations reviewed the evidence and concluded that at appropriate doses and with proper monitoring, misoprostol is both safe and effective for induction. It remains one of the most studied medications in obstetrics, and its off-label status reflects regulatory history more than clinical concern.