Misoprostol has four primary effects. 

1. Cytoprotection of the gastrointestinal mucosa 
2. Uterotonic
3. Diarrhea 
4. Abdominal pain (diarrhea and abdominal pain fall under adverse effects).[1] 

Currently, misoprostol is FDA approved only for the prevention and treatment of NSAID-induced gastric ulcers in patients taking NSAIDs and at high risk for ulceration. It has an indication (but not FDA approved) in the short-term treatment of active duodenal or gastric ulcers with other etiologies.[2]

Although clinicians use misoprostol around the world in gynecology and obstetrics, however, none of these indications are FDA approved. 

The combination of misoprostol and mifepristone has reported widespread use for medical abortions with an acceptable safety profile. Unfortunately, reports of significant adverse events without significant data have hindered FDA approval. Therefore, there is an extensive debate between the governing societies regarding the dosing standardization of this regimen. It may receive approval once there is additional research, and there is an agreed dosing strategy.[1]

It is used for termination of pregnancy in the first and second trimesters as either monotherapy or combination with intramuscular methotrexate.[1] Clinicians also use misoprostol as expectant management of missed and incomplete abortions. 

At much smaller doses, misoprostol is useful for inducing cervical ripening and induce labor in full-term pregnancies. It may also be employed to induce labor following intrauterine fetal demise.[3]

After labor, it also has a use for the treatment of postpartum uterine bleeding upon failure of uterine massage, and/or when other uterotonic medications are not readily available.[4]

Misoprostol is a synthetic prostaglandin E1 analog that inhibits basal and nocturnal gastric acid secretion through direct stimulation of prostaglandin E1 receptors on parietal cells in the stomach. This action inhibits gastric acid secretion secondary to stimulation from food, alcohol, NSAIDs, histamine, caffeine, etc.  This effect tends to have a dose-dependent relationship. 

Misoprostol induces mucus and bicarbonate secretion as well edema of the mucosa and submucosa, which causes thickening of the mucosal bilayer, which results in a reduced backflow of hydrogen ions and improved regulation of mucosal blood flow, which ultimately leads to the preservation of the mucosa's ability to produce new cells.[1]

Uterotonic effects are caused by prostaglandin binding to smooth muscle cells in the uterine lining; this is responsible for its abortifacient properties, as well as its ability to promote labor and cervical ripening. Cervical dilation is produced primarily via degradation of collagen in the connective tissue of the stroma and reduction in cervical tone from increased amplitude and frequency of contractions. Its uterotonic properties are also useful to help decrease postpartum bleeding.[5][6]

Abdominal pain and diarrhea appear to be a result of exposure to the misoprostolic acid released during metabolism, as symptoms seem to correlate with the misoprostolic acid peak plasma concentration.[1]

Currently, the only FDA approved route of administration is oral.  Although not FDA approved, misoprostol may also be administered sublingually, buccally, vaginally, or rectally via digital placement of tablets or suppositories. Despite a plethora of studies comparing the efficacy and safety profiles of the different routes of administration for obstetric uses, there are no definitive conclusions regarding this use.[7] 

It is best to take medication at night time with meals to minimize GI upset when given orally. Do not take with magnesium-containing antacids, as this combination may contribute to misoprostol-induced diarrhea. 

The most commonly reported adverse effects are generally mild and include shivering/chills, diarrhea, abdominal pain, hyperthermia, nausea, vomiting, flatulence, constipation, dyspepsia, headache, breakthrough bleeding, and menstrual irregularity. Less reported mild side effects include syncope, lethargy, weakness, and vertigo. 

Moderate to severe reactions are less common and include hypotension, sinus tachycardia, fetal bradycardia, uterine contractions and pain, vaginal bleeding, edema, myocardial infarction, uterine rupture, cervical laceration, fetal death, teratogenesis, pulmonary embolism, anaphylactoid reactions, and thrombosis. 

The most frequently encountered side effects include self-limiting diarrhea and abdominal pain, thought to be secondary to exposure to the misoprostolic acid released during its metabolism. The basis for this line of reasoning is the observation that symptom severity tends to correlate with misoprostolic acid’s peak plasma concentration.[1]

Fever and chills are relatively common and thought to be secondary to the effect of prostaglandin on the hypothalamus. These mild side effects occur most commonly when misoprostol is administered in relatively large doses, such as to treat postpartum hemorrhage.[8] 

Congenital defects correlate with exposure to misoprostol in early pregnancy. However, no data shows misoprostol to be directly related to embryotoxic/fetotoxic or teratogenic effects. Mutagenetic studies have been negative. Defects appear to be due to a decrease in fetal blood supply during contractions induced by misoprostol. Additionally, there seems to be a relationship between the time of exposure and the range of defects observed. The most common defects are in the central nervous system and limbs. Mobius syndrome also correlates with misoprostol exposure.[8]

The use of prostaglandins in cervical ripening correlates with an increased risk of tachysystole, non-reassuring fetal heart rate, and fetal hypoxemia.[6]

There is a risk for uterine rupture with misoprostol use. This risk tends to be highest when misoprostol is used for labor induction in the third trimester, especially in conjunction with other risk factors such as previous caesarian section. Rupture is rare during a first-trimester medical abortion using misoprostol. However, as with all uterine ruptures, there is a risk for subsequent uterine infection.[8]

Misoprostol is contraindicated in those with previous allergic reaction or hypersensitivity to prostaglandin. Those at risk for gastric ulcers secondary to NSAID use and are pregnant should not take misoprostol given the adverse effects reported during pregnancy.

Besides allergic reactions, there are no absolute contraindications for misoprostol's gynecologic and obstetric indications given the lack of society-approved guidelines for these uses. Contraindications are relative to the drug's desired effect and should be individualized depending on each patient's risk factors. For example, given the increased risk of uterine rupture, those with previous caesarian sections should not take misoprostol to induce a medical abortion.[9]