CYP2B6*38 (c.186T>A, p.Y62X; c.516G>T, p.Q172H/splice defect; c.785A>G, p.K262R) – No function: CYB2B6*38 is assigned no function. CYP2B6*38 contains the variants which define CYP2B6*6 in addition to a third variant which causes a premature stop codon. CYP2B6*38 was identified in a patient taking efavirenz who developed neurologic symptoms and was found to have an efavirenz plasma concentration 40-fold above normal limit. Efavirenz was discontinued and efavirenz plasma concentrations returned to normal after 10 weeks in addition to resolution of neurologic symptoms (23640958). Therefore, consensus among experts was no function based on limited evidence.