What is mifepristone, and how does it work (mechanism of action)?
Mifepristone is a synthetic steroid with
antiprogesterone and antiglucocorticoid effects. It is used for terminating
pregnancy and treating people with Cushing syndrome. Progesterone is a female
hormone and the principal progestational hormone. Progesterone prepares the
uterus (the womb) to receive and sustain the fertilized egg andis an important
hormone for sustaining pregnancy. Mifepristone terminates early pregnancy by
blocking the activity of progesterone at progesterone receptors. It also
stimulates contraction of the uterus. Early pregnancy is considered to be = 49
days (7weeks) since the last menstrual period began. Mifepristone must be used
in combination with misoprostol for the purpose of termination of pregnancy. The
FDA approved this combination treatment in September 2000.
Cortisol is a metabolite (break down product) of the hormone cortisone.
Cortisol is an essential factor in many processes including the proper
metabolism of starches, and it is the major natural glucocorticoid in humans.
People with Cushing syndrome produce too much cortisol, and, among many other
effects, develop high glucose (sugar) levels in the blood. Mifepristone reduces
blood glucose levels in people with Cushing syndrome by blocking the activity of
What brand names are available for mifepristone?
Is mifepristone available as a generic drug?
Do I need a prescription for mifepristone?
What are the side effects of mifepristone?
Commonly reported side effects include vaginal bleeding,
cramping, nausea, vomiting, diarrhea, dizziness, back pain, and tiredness. Less
common but severe side effects include allergic reactions, low blood pressure,
loss of consciousness, infections after abortion, ruptured ectopic pregnancy,
shortness of breath, rapid heartbeat (tachycardia), and hematometra (collection
of blood in the uterus).
What is the dosage for mifepristone?
Treatment with mifepristone and misoprostol requires three separate
- Day 1: Three 200 mg tablets (600
mg) of mifepristone are taken as a single dose.
- Day 3: 400 mcg of misoprostol is
given orally unless abortion has been confirmed.
- Day 14: No medication
administered. Patient returns for a post-treatment examination to confirm that a
complete termination of pregnancy has occurred.
The dose for treating Cushing syndrome is 300 mg daily initially. The dose
may be increased to 1200 mg daily.
Which drugs or supplements interact with mifepristone?
Ketoconazole, itraconazole (Sporanox), erythromycin, and
grapefruit juice may increase blood levels of mifepristone by inhibiting the
enzyme responsible for metabolizing (breaking down) mifepristone. Rifampin,
dexamethasone, St. John’s Wort, phenytoin, phenobarbital, and carbamazepine may
decrease blood levels of mifepristone by increasing the activity of the enzyme
responsible for metabolizing mifepristone and decrease the effectiveness of
mifepristone. Mifepristone may inhibit liver enzymes which are responsible for
the metabolism of various drugs, resulting in increased blood levels of these
Is mifepristone safe to take if I’m pregnant or breastfeeding?
Mifepristone is used for the termination of pregnancy through the
49th day of pregnancy. Otherwise, it should not be used during pregnancy because
it will terminate the pregnancy.
Mifepristone is secreted into breast milk. Due to the risk
of adverse effects,
breastfeeding mothers should decide whether to discontinue
breast-feeding or mifepristone.
What else should I know about mifepristone?
What preparations of mifepristone are available?
Tablets: 200 and 300 mg
How should I keep mifepristone stored?
Tablets should be stored at room temperature, 15 C – 30 C (59 F – 86
F). Optimal storage temperature is 25 C (77 F).
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Medically Reviewed on 3/14/2019
FDA Prescribing Information