Efavirenz and Mifepristone interaction
Efavirenz and Mifepristone: both prescribing labels flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
From the Mifepristone label · effective 2025-09-25
CYP3A inducers: Do not use mifepristone with CYP3A inducers ( 7.3 ).
Avoid co-administration of mifepristone and CYP3A inducers such as rifampin, rifabutin, rifapentin, phenobarbital, phenytoin, carbamazepine, and St.
Drugs metabolized by CYP2B6: Use of mifepristone should be done with caution with bupropion and efavirenz ( 7.5 ).
…warfarin, and repaglinide) should be used at the smallest recommended doses, and patients should be closely monitored for adverse effects. [See Clinical Pharmacology ( 12.3 )] 7.5 Drugs Metabolized by CYP2B6 Mifepristone is an inhibitor of CYP2B6 and may cause significant increases in exposure of drugs that are metabolized by CYP2B6 such as bupropion and efavirenz.
Since no study has been conducted to evaluate the effect of mifepristone on substrates of CYP2B6, the concomitant use of bupropion and efavirenz should be undertaken with caution. [See Clinical Pharmacology ( 12.3 )] 7.6 Use of Hormonal Contraceptives Mifepristone is a progesterone-receptor antagonist and will interfere with the effectiveness of hormonal contraceptives.
From the Efavirenz label · effective 2024-03-31
Hormonal contraceptives: Oral Ethinyl estradiol/ Norgsetimate Implant Etonogestrel ↑ active metabolites of norgestimate * ↓ etonogestrel A reliable method of barrier contraception should be used in addition to hormonal contraceptives.
A reliable method of barrier contraception should be used in addition to hormonal contraceptives.
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Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.