No clinically significant interaction was observed when efavirenz (600 mg daily) and delamanid (100 mg twice daily) were coadministered. There was no change in delamanid Cmax and a 3% decrease in AUC; efavirenz Cmax and AUC both decreased by 6%. However, the overall incidence of adverse effects was higher during concomitant dosing with delamanid and efavirenz compared to either medication alone. A higher rate of neuropsychiatric adverse effects (e.g., euphoric mood and abnormal dreams) was observed with delamanid plus efavirenz compared to either drug alone, but no subject discontinued the study because of neuropsychiatric events or had serious neuropsychiatric adverse effects. Delamanid has a possible risk of QT prolongation and/or TdP on the CredibleMeds.org website. Efavirenz was shown to prolong the QT interval above the regulatory threshold of concern in homozygous carriers of the CYP2B6*6/*6 allele (i.e. 516T variant in the gene encoding CYP2B6). The European product label for efavirenz contraindicates coadministration with a drug with a known risk of Torsade de Pointes whereas the American product label for efavirenz recommends that alternatives should be considered. As the potential risk of a QT interval prolongation relates specifically to homozygous carriers of CYP2B6*6/*6 and given the accumulated years of safety data with efavirenz and such drugs, the contraindication is not reflected in the colour coding of this interaction summary.