Coadministration has not been studied. Carvedilol undergoes glucuronidation and additional metabolism via CYP2D6 and to a lesser extent CYPs 2C9 and 1A2. Efavirenz could potentially increase carvedilol concentrations via CYP2C9 inhibition or decrease carvedilol concentrations via induction of glucuronidation (UGT1A1). The net effect on carvedilol concentrations is difficult to predict but likely to be moderate in magnitude. No a priori dosage adjustment is required.