Mifeprex Drug Interactions: What to Avoid and What to Tell Your Doctor

Before taking Mifeprex (mifepristone), it is important to tell your healthcare provider about all medications, supplements, and herbal products you currently use. Mifepristone is metabolized by the CYP3A4 liver enzyme system, which means it interacts with dozens of other substances that either inhibit or induce this enzyme. Some interactions are contraindications — meaning Mifeprex should not be taken at all with those substances. Others require caution or dose adjustments. Here is what you need to know.

Category 1: Contraindicated — Do Not Take with Mifeprex

These medications should not be used together with Mifeprex because the combination can cause serious harm:

Blood thinners (anticoagulants): Warfarin (Coumadin), heparin, and similar anticoagulants are contraindicated because Mifeprex itself causes bleeding and anticoagulants can lead to excessive, life-threatening hemorrhage. Do not take Mifeprex if you are currently on any anticoagulant therapy.

Long-term systemic corticosteroids: Patients taking ongoing oral, injectable, or inhaled steroids (prednisone, methylprednisolone, dexamethasone, etc.) for chronic conditions should not take Mifeprex. The anti-glucocorticoid effect of mifepristone can precipitate adrenal insufficiency in patients whose adrenal glands are already suppressed from long-term steroid use.

Certain CYP3A4 substrates (narrow therapeutic range): For patients using the higher-dose mifepristone (Korlym, 300 mg/day) for Cushing's syndrome: simvastatin, lovastatin, cyclosporine, fentanyl, pimozide, quinidine, sirolimus, and tacrolimus are contraindicated because mifepristone significantly increases their blood levels, potentially causing toxicity.

Category 2: Use with Caution — Increased Bleeding Risk

NSAIDs (nonsteroidal anti-inflammatory drugs): Aspirin and other NSAIDs like ibuprofen and naproxen have antiplatelet effects that may increase bleeding risk with Mifeprex. Aspirin is specifically listed as contraindicated in some references because of its antiplatelet activity. Ibuprofen is commonly used to manage cramping during medication abortion, but should be used at standard doses and only as needed. Discuss with your provider before using any NSAIDs.

Category 3: CYP3A4 Inhibitors — May Increase Mifepristone Levels

These substances inhibit the CYP3A4 enzyme that breaks down mifepristone. Taking them together can increase mifepristone blood levels, potentially intensifying side effects:

Antifungals: Ketoconazole, itraconazole, fluconazole

Certain antibiotics: Erythromycin, clarithromycin

HIV protease inhibitors: Ritonavir, lopinavir, atazanavir

Grapefruit juice: Grapefruit and grapefruit juice inhibit CYP3A4 and can increase mifepristone blood levels. Avoid grapefruit during and around the time of your Mifeprex regimen.

Category 4: CYP3A4 Inducers — May Reduce Mifepristone Efficacy

These substances speed up the CYP3A4 enzyme, causing mifepristone to be broken down more quickly. This can lower mifepristone blood levels and potentially reduce effectiveness:

Rifampin (antibiotic): Potent CYP3A4 inducer; avoid if possible or confirm efficacy with your provider

St. John's Wort: This common herbal supplement induces CYP3A4 and should be stopped before taking Mifeprex. Tell your provider if you take any herbal products.

Anticonvulsants: Phenytoin (Dilantin), phenobarbital, and carbamazepine (Tegretol) are all CYP3A4 inducers. If you take any of these, discuss with your prescriber whether Mifeprex remains effective.

Dexamethasone: Both a CYP3A4 inducer and a corticosteroid — two reasons to avoid combination with Mifeprex.

What to Tell Your Doctor Before Taking Mifeprex

At your appointment, provide a complete list of all medications — including over-the-counter drugs, vitamins, herbal supplements, and recreational substances. Specifically mention:

Any blood thinner or anticoagulant (even aspirin taken daily)

Any steroid medication (pill, injection, nasal spray, or inhaler used for chronic conditions)

Any antifungal medication (topical antifungals like clotrimazole cream are typically not a concern, but oral antifungals are)

Herbal supplements, especially St. John's Wort

Any seizure medication

For more on what to expect after taking Mifeprex, see: Mifeprex side effects: what to expect and What is Mifeprex?.