- Medications with significant drug-drug interactions with efavirenz:voriconazole, terfenadine, astemizole, cisapride, ergot alkaloids (dihydroergotamine, ergonovine, ergotamine, methylergonovine), midazolam, triazolam, St. John's wort, carbamazepine, phenytoin, phenobarbital, rifampin, pimozide, bepridil