Mifegest

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Mifegest

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Medically reviewed

Marina Burgos

Last updated on 22/12/2025

This page provides general, reference-level information compiled from official medical sources. It is not a substitute for professional medical advice, diagnosis, or treatment. For decisions about your health, please consult a qualified healthcare professional.

Overview of Mifegest

Property Description
Active Ingredient Mifepristone (INN)
Form Oral Tablet
Pharmacological Class Progesterone Receptor Antagonist (Antiprogestin)
General Purpose To disrupt progesterone-dependent physiological processes
Origin Synthetic 19-norsteroid derivative

Mifegest: Defining the Drug Entity and Its Pharmaceutical Class

Mifegest is a prescription-only synthetic medication containing the active ingredient Mifepristone (INN), a compound historically known as RU-486. Mifepristone is formally classified as a Progesterone Receptor Antagonist, often called an antiprogestin. This substance belongs to the chemical class of synthetic 19-norsteroid derivatives. The drug's functionality is clinically recognized for its potent ability to interfere with hormonal processes.

The fundamental identity of Mifepristone is rooted in its highly selective blocking mechanism: it acts as a hormone blocker by competitively occupying the progesterone receptors in cells, thereby inhibiting the signals that the natural hormone progesterone would normally transmit. This classification is central to its therapeutic function, as progesterone is essential in maintaining specific uterine conditions.

Composition, Form, and General Therapeutic Role

Mifegest is manufactured as a single-ingredient product and is formulated exclusively into an oral tablet for systemic administration. The final preparation consists of the active substance, Mifepristone, combined with essential solid excipients, such as cellulose and starch, to ensure stability and proper absorption. This oral route is a key differentiating factor, enabling rapid, systemic delivery of the antagonist.

The general therapeutic purpose of Mifegest is directly derived from its antagonistic action on the progesterone receptor. The drug's mechanism leads to the cessation of progesterone-dependent processes, causing a disruption of the uterine lining (endometrium). Mifepristone works by interfering with the hormone activity necessary to sustain certain conditions in the body. Therefore, the overall role of the medicine is to initiate or facilitate physiological changes by terminating the stabilizing, progesterone-mediated effects on reproductive tissues, which is a typical use scenario for this class of medicine.

Regulatory References

  1. Mifepristone
  2. U.S. National Library of Medicine

What side effects are possible with Mifegest?

Possible Side Effects and Safety Information

The safety profile of Mifepristone (Mifegest), a Progesterone Receptor Antagonist, is documented by official regulatory bodies like the FDA and EMA and varies based on the condition being treated (early pregnancy management or Cushing's syndrome).

Side effects are officially categorized by the system they affect and their frequency, which ranges from very common to rare.

Classification of Adverse Reactions

The most frequent (Very Common, ge 10%) adverse reactions include gastrointestinal symptoms (nausea, vomiting, diarrhea), headache, fatigue, and reproductive system effects (uterine cramping, vaginal bleeding, or spotting). For patients using the medicine for Cushing's syndrome, common adverse reactions also include decreased blood potassium (hypokalemia) and hypertension.

Frequency Examples of Officially Listed Reactions
Very Common Nausea, Vomiting, Diarrhea, Headache, Fatigue, Uterine Cramping
Common Dizziness, Heavy uterine bleeding, Musculoskeletal pain, Hypertension

Documented Serious Safety Concerns

Although rare, regulatory documents highlight the potential for serious adverse reactions. These include cases of severe hemorrhage requiring intervention and serious bacterial infection or septic shock, particularly in the context of early pregnancy management. When used for Cushing's syndrome, a key safety constraint is the potential for adrenal insufficiency due to the drug's mechanism.

Population-Specific and Time-Related Safety

Safety limitations are noted for specific populations; for example, the medicine is not recommended for individuals with severe hepatic impairment. Furthermore, specific safety patterns are tied to duration: vaginal bleeding is an expected physiological effect that may persist for several weeks, while endometrial hypertrophy is a documented event associated with long-term exposure in some uses.

Overdose and Emergency Response

Overdose and when to seek help

The regulatory profile for Mifegest overdose emphasizes managing severe complications that result from exaggerated pharmacological effects, rather than acute toxicity. Official documents indicate that exposure to very high single doses has not resulted in serious or unexpected adverse events in clinical studies. However, the primary life-threatening concerns are severe hemorrhage (heavy vaginal bleeding) and septic shock or fatal infections, which can be complications of the treatment regimen.

Required Emergency Actions

Immediate medical attention must be sought if you suspect an overdose or experience any of the following severe signs, as mandated by regulatory authorities:

  • Heavy vaginal bleeding or bleeding that lasts longer than expected.
  • Fainting (syncope) or dizziness.
  • Severe abdominal pain.
  • Fever of 100.4 F (38 C) or higher lasting for more than a few hours.

Clinical Management Statements

Official labeling confirms that no specific antidote is known for Mifegest. Treatment for suspected over-exposure or resulting severe complications is symptomatic and supportive. This may involve procedural interventions, such as blood transfusions or the administration of intravenous fluids, if necessary to manage complications like hypovolemia. Caution regarding over-exposure risk is noted for patients with pre-existing hepatic or renal impairment.

Therapeutic Uses of Mifegest

What Mifegest Treats: Main Uses and Benefits

Mifegest is commonly used to help with conditions characterized by periods of heightened symptoms and is generally considered relevant across therapeutic domains involving hormonal and endocrine management. The medication is applied in clinical settings that involve acute or disruptive symptom patterns.

The medication is relevant for easing symptoms and providing support across three main therapeutic areas: managing an early intrauterine pregnancy, controlling severe hyperglycemia in endogenous Cushing's syndrome, and symptomatic relief for uterine leiomyomas (fibroids).

The primary benefit is offering non-surgical options for management, which helps to ease the overall symptom load associated with acute episodes. “The treatment is applied in scenarios where additional management of discomfort is required and functional stability becomes affected.”


Quick Fact: Relief for Systemic Strain Mifegest is commonly used to help address symptom clusters that may become disruptive, such as excessive bleeding, pain, and metabolic imbalances, supporting the patient during difficult episodes.

Management of Early Intrauterine Pregnancy

This medication is applied in clinical settings that involve the management of an early intrauterine pregnancy, typically providing a non-surgical alternative for cessation. The treatment is relevant for individuals seeking to resolve a pregnancy within a specific gestational timeframe. The primary benefit is offering a non-surgical option for pregnancy management, which helps to ease the overall symptom load associated with this acute episode and supports the patient during periods of heightened physiological change.

Control of Severe Metabolic Disturbances

Mifegest is commonly used to help with symptom clusters related to severe systemic imbalance, specifically managing high blood sugar levels (hyperglycemia) in adults with endogenous Cushing's syndrome. This use is relevant when supportive symptom management is appropriate and other primary treatments have been unsuccessful or are not feasible. This supports the patient during difficult episodes by easing distress and assists with maintaining functional stability when symptoms are more noticeable.

Symptomatic Relief for Uterine Fibroid-Related Issues

The medication may be part of symptomatic management for uterine leiomyomas (fibroids), and is relevant for easing symptoms related to physical discomfort and systemic strain. It is commonly used to help address symptom clusters that may become disruptive, such as excessive bleeding (menorrhagia) and associated pain or pressure. This supports the patient during difficult episodes by easing distress and contributes to improved comfort during symptomatic periods.

Regulatory References

  1. NIH MedlinePlus overview

Eligibility and Restrictions for Use

Mifegest's eligibility rules are defined by regulatory authorities and depend on the approved use.

Contraindicated Populations

The medicine must not be used by patients with specific underlying conditions or concurrent treatments, as this is an absolute prohibition stated in official labeling:

  • Chronic adrenal failure or concurrent long-term corticosteroid therapy.
  • Hemorrhagic disorders or concurrent anticoagulant therapy.
  • Inherited porphyrias or known allergy to mifepristone or prostaglandins.

For medical termination of pregnancy, use is also contraindicated in cases of confirmed or suspected ectopic pregnancy or if an IUD (intrauterine device) is in place.

Conditional and Restricted Use

Use requires specific precautions or is limited in certain populations:

  • Organ Impairment: Patients with severe hepatic impairment are generally not recommended for treatment. For mild-to-moderate impairment or renal impairment, caution is advised, and dose restrictions may apply.
  • Age: Mifegest is approved for adults and for pregnant females aged 17 and younger for termination of pregnancy. However, safety and efficacy have not been established in the geriatric population or in children for the Cushing's syndrome indication.
  • Pregnancy/Lactation: The drug is contraindicated in pregnancy when used for Cushing's syndrome. Breastfeeding is not an issue after a single dose for termination, but long-term breastfeeding should be avoided during chronic therapy.

What should I know about interactions with other medicines?

Interactions with other medicines and products

Mifegest (Mifepristone) has documented interaction patterns based on its roles as a metabolic enzyme modulator and a receptor-level antagonist. Regulatory information classifies these interactions into strict constraints for co-administration.

Contraindicated and Restricted Combinations

Official labeling contraindicates co-administration with several substance classes due to the risk of serious interaction outcomes. This includes patients requiring long-term corticosteroid therapy due to Mifepristone's potent antiglucocorticoid effect. The drug is also contraindicated with CYP3A4 substrates that possess a narrow therapeutic range (e.g., cyclosporine, fentanyl, tacrolimus) because Mifegest acts as a CYP3A4 inhibitor, increasing their exposure. Furthermore, use is restricted in patients with hemorrhagic disorders or those concurrently using anticoagulants or antiplatelet agents, such as aspirin, due to increased risk of excessive bleeding.

Pharmacokinetic and Timing Rules

Co-administration with strong CYP3A4 inhibitors (e.g., ketoconazole, erythromycin) may cause a clinically significant pharmacokinetic interaction, increasing Mifepristone's serum concentrations. Conversely, CYP3A4 inducers (e.g., rifampin, carbamazepine, St. John's Wort) may lower Mifepristone’s concentration. A specific timing rule mandates that co-administered prostaglandins, such as Misoprostol, must be administered within a 24 to 48-hour window after Mifegest.

Mechanism of Action

Interrupting Progesterone Signaling (Receptor Antagonism)

Mifegest ( Mifepristone) primarily acts as an antagonist for the progesterone receptor (PR). It binds with high affinity to the PR in target tissues, such as the uterine lining, thereby interrupting the hormone signal that normally supports the maintenance of the uterine lining (decidua). This interruption leads directly to the destabilization and breakdown of the specialized endometrial tissue.


Inducing Uterine Muscle Activity (Prostaglandin Cascade)

The blockade of the PR initiates a downstream mechanistic cascade that increases the release of and enhances the tissue's sensitivity to local mediators called prostaglandins. This heightened activity causes the uterine smooth muscle to undergo strong, rhythmic contraction and promotes the softening and opening of the cervix.


Modulating Glucocorticoid Responses (Secondary Target)

Mifepristone also functions as an antagonist at the Glucocorticoid Receptor (GR). This interaction alters signaling pathways in tissues containing the GR, expanding the drug's scope of action beyond the reproductive tract.

Dosage and Administration Information

How to Use Mifegest — Official Administration Guidelines

Administration of Mifegest (Mifepristone) follows specific regimens strictly defined, varying based on the intended purpose. The medication is formulated as an oral tablet and the oral route is the only approved method of administration.


Official Usage Patterns

Usage Context Key Administration Rule Standard Dose/Schedule
Chronic Metabolic Management Must be taken once daily and with a meal. The starting dose is 300 mg, which may be gradually increased up to a maximum of 1200 mg per day.
Sequential Short-Term Regimen Administered as a single dose followed by another medication 24 to 48 hours later. A single oral dose of 200 mg is typically used, although certain labels have also included a 600 mg dose.

Key Procedural and Adjustment Rules

For the chronic metabolic regimen, dose increases, when necessary, must occur no more frequently than every two to four weeks. The tablets used for chronic management must be swallowed whole and should not be split, crushed, or chewed.

Specific dose limitations are mandated for individuals with existing organ impairment. For patients with mild to moderate kidney or liver impairment, the daily dose must be limited to a maximum of 600 mg.

These official instructions establish clear, standardized protocols that govern the entire administration process, ensuring consistent application of the drug according to established standards.

Recent Clinical Evidence

Recent Clinical Evidence Overview

Clinical research on mifepristone focuses primarily on its use in combination with a prostaglandin analog, misoprostol, for the medical termination of an early intrauterine pregnancy. The agent's activity is related to the antagonism of the progesterone receptor, a mechanism essential for its use in this context.

Efficacy and Study Outcomes

Numerous studies, including randomized controlled trials, have investigated the efficacy of the combined regimen. The standard protocol involves taking a dose of mifepristone followed by misoprostol 24 to 48 hours later.

  • Success Rates: Across various studies using this two-drug regimen, success rates—defined as complete termination without the need for a surgical procedure—have been observed in the range of 93% to 98% when used within the approved gestational limits (typically up to 70 days or 10 weeks). Efficacy may vary slightly based on gestational age.
  • Comparative Use: Research has explored outcomes when the agent is combined with misoprostol compared to misoprostol used alone. Studies suggest the addition of mifepristone significantly increases the effectiveness of the regimen.

Safety and Tolerability

The safety profile is considered well-established through decades of clinical use and post-marketing surveillance. Serious adverse events are rare, with rates typically reported as less than 1%.

Common Expected Events Serious Adverse Events (Rare)
Uterine cramping and bleeding Severe infection
Nausea, vomiting, diarrhea Hemorrhage requiring transfusion

Most reported adverse events, such as cramping and bleeding, are an expected consequence of the treatment and are typically managed with over-the-counter pain medication. Follow-up research continues to monitor the long-term health outcomes associated with the treatment.

Key Studies & References

  1. Medical Abortion: Efficacy and Safety (ACOG Clinical Practice Guideline No. 228)
  2. NICE Guideline: Termination of pregnancy: Medical methods (Mifepristone and Misoprostol)

Frequently Asked Questions (FAQ)

Common questions about Mifegest (FAQ)

Q: How quickly does Mifegest start working?

A: The active ingredient in Mifegest is absorbed relatively quickly after it is taken. However, the complete process leading to the intended physical outcome is a two-step regimen. The second medication in the regimen is taken 24 to 48 hours later, and the main physical effects are typically observed within hours after taking the second drug.

Q: What is the typical duration of effect for Mifegest?

A: The active drug is eliminated from the body slowly, with serum levels often remaining detectable for about 11 days. The expected physical effects, such as vaginal bleeding or spotting, may persist for an average of 9 to 16 days. Official information indicates that this effect could last for 30 days or more in some individuals.

Q: Can Mifegest be used after a certain number of weeks?

A: Official regulatory indications for the short-term regimen specify that the medicine is approved for use through 70 days, which is equivalent to 10 weeks of gestation. This limit is based on the data used to establish the safety and effectiveness of the regimen.

Q: Is Mifegest the same as 'the abortion pill'?

A: Official drug information and patient guides refer to the complete treatment regimen—which involves Mifegest (mifepristone) followed by a second medicine (misoprostol)—as being used for 'medical termination of pregnancy.' The complete treatment regimen, which includes Mifegest, is commonly referenced in patient materials as 'the abortion pill.'

Q: What is the difference between Mifegest and Cytotec (misoprostol)?

A: Mifegest (mifepristone) is a Progesterone Receptor Antagonist that functions by blocking a hormone necessary to maintain the pregnancy. Misoprostol is a different type of medicine (a prostaglandin analog) that is taken later to induce uterine contractions. Both medicines work together in the approved regimen.

Q: What foods or drinks should be avoided when taking Mifegest?

A: Official product information advises against the consumption of grapefruit or grapefruit juice while using this medicine. This is due to potential interaction that affects the concentration of the medicine in the body. For one of the medicine’s other official uses, it is directed to be taken with a meal.

Q: Is it normal to feel nauseous after taking Mifegest?

A: Official regulatory documents list nausea, vomiting, and diarrhea as very common adverse reactions. This classification indicates that they are highly expected side effects that may affect many patients who use the medicine.

Q: Can I take pain relief medicine with Mifegest?

A: Due to the expected cramping, official patient information often mentions that over-the-counter pain relievers, such as ibuprofen or acetaminophen, may be used for managing discomfort. Official warnings generally advise against using aspirin or similar antiplatelet agents because they may increase the risk of excessive bleeding.

Q: Can I drive after taking Mifegest?

A: Official labeling lists side effects such as headache, fatigue, and dizziness. Patients are cautioned that these symptoms may affect their ability to safely operate a vehicle or heavy machinery.

Q: What should be done if I vomit shortly after taking Mifegest?

A: If the dose of Mifegest is vomited shortly after ingestion (typically within the first hour), official patient instructions indicate that the healthcare provider should be contacted immediately for guidance. This is to ensure the appropriate amount of medication has been absorbed.

Q: How is the process described when using Mifegest at home?

A: The second medication in the regimen (misoprostol) is often taken by the patient at home, 24 to 48 hours after taking Mifegest. Official instructions recommend patients discuss an appropriate location for this step with their healthcare provider, as the primary physical process may begin within hours after the second medicine is administered.

Q: Do studies suggest any long-term physical effects from using Mifegest?

A: Official safety data has been gathered over decades of use and post-marketing surveillance. There is no information in the regulatory documents linking the approved short-term regimen to long-term physical health problems or complications in future pregnancies. However, adverse events are documented for the long-term use of the medicine for other conditions.

Q: What happens if Mifegest does not work?

A: Clinical studies report very high success rates, but in the event of a procedure failure, an incomplete termination may occur. Official documents state that if this happens, the healthcare provider may offer the patient a further dose of the second medicine or discuss a surgical procedure to complete the termination.

Q: Does Mifegest affect future fertility?

A: Official patient information indicates that a new pregnancy can occur shortly after treatment, even before periods have returned, and advises the use of contraception. The documents contain no information suggesting the single-dose regimen negatively affects a person's ability to become pregnant later in life.

Q: Is it required to have a follow-up appointment after using Mifegest?

A: Yes, official patient management guidelines require a follow-up assessment with the healthcare provider. This check should occur approximately 7 to 14 days after taking Mifegest. The purpose is to confirm that the complete termination has successfully occurred.

Q: Does Mifegest affect mood or mental health?

A: Official documents list physical symptoms such as headache, fatigue, and dizziness as common adverse reactions. Specific mood or long-term mental health effects are not listed as direct side effects of the medication in the core regulatory documents.

Q: Are there any known interactions between Mifegest and herbal supplements?

A: Official patient guides require individuals to discuss with their healthcare provider the use of any other prescription, over-the-counter medicines, vitamins, or herbal supplements during the treatment period. This is because certain supplements may interact with the way the body processes the medication.

Q: How does the mechanism of action of Mifegest compare to a natural miscarriage?

A: Patient-facing materials sometimes describe the physical process resulting from the medication as being similar to a natural early miscarriage. In both cases, the physiological response involves uterine cramping and bleeding to empty the uterus.

Q: Is it common for people to need a follow-up procedure after taking Mifegest?

A: No, it is not common. Clinical studies report high success rates for complete termination without the need for a surgical procedure. While a small percentage of individuals (around 2%–7%) may require a follow-up procedure to complete the termination, this is not the typical outcome.

Q: Are there specific instructions for what to eat before taking Mifegest?

A: Specific instructions on what to eat before the short-term regimen are generally not detailed in official patient guides. The focus is usually on avoiding grapefruit and grapefruit juice, as well as the instruction for the drug's chronic use to be taken with a meal.

Q: Do doctors prescribe Mifegest for uses other than the main indication?

A: Mifepristone, the active ingredient in Mifegest, has two distinct regulatory approvals. One is for the medical termination of intrauterine pregnancy, and the other (under a different brand name) is for managing high blood sugar levels in patients with Cushing's syndrome.

Q: Can a person be allergic to Mifegest?

A: Yes. Official labeling lists a known allergy to mifepristone or prostaglandins as a contraindication. Serious allergic reactions, including severe swelling (angioedema) and anaphylaxis, have been reported in safety documents.

Q: Why is it called 'medical' termination and not 'surgical'?

A: The term 'medical' termination is used to differentiate the process from a 'surgical' procedure. Medical termination is initiated and completed using medication (pills), whereas a surgical procedure involves an invasive process.

Q: Does Mifegest cause changes to the menstrual cycle afterward?

A: Following the short-term regimen, a new pregnancy can occur very quickly, even before the return of a normal menstrual period. For individuals using the medicine for long-term conditions (Cushing’s syndrome), disruption to the normal menstrual cycle is a documented adverse event.

Q: What are the requirements for the healthcare facility providing Mifegest?

A: In the US, the medicine is part of a Risk Evaluation and Mitigation Strategy (REMS) program. This program mandates that prescribers and pharmacies must be certified. The program also requires that certified prescribers have access to emergency care, including surgical intervention and blood transfusion services.

Q: Why does Mifegest have a Risk Evaluation and Mitigation Strategy (REMS) in the US?

A: The medicine is subject to the REMS program because of the potential for rare but serious complications. These include severe hemorrhage (bleeding) and serious bacterial infection or sepsis. The REMS ensures that specific conditions are met when prescribing and dispensing to mitigate these risks.

How should Mifegest be stored and disposed of?

How to Store and Dispose of Mifegest?

The official labeled requirements define strict conditions for storage and disposal to maintain the quality of the medication.

Storage Requirements

Condition Requirement
Temperature Store at controlled room temperature, between 20 C to 25 C (68 F to 77 F). Brief excursions are permitted.
Protection Protect the medicine from heat, moisture, direct light, and keep it from freezing.
Handling Keep the medicine in a closed container, and store it out of the reach of children.

Disposal Instructions

Regulatory instructions specify that unused or outdated medicine must be discarded properly. Patients should ask a healthcare professional, such as a doctor or pharmacist, for instructions on how to dispose of unused medicine. Expired product is managed as pharmaceutical waste according to established hazardous waste guidelines, typically through licensed facilities for processing and incineration.

Attention! Always consult to a doctor or pharmacist before using pills or medicines.

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