CYP2B6*5 (c.1459C>T, p.R487C) - Normal function: CYP2B6*5 is assigned normal function based on in vivo (heterozygous and homozygous patients) and in vitro studies. Multiple studies evaluating efavirenz plasma concentrations among patients with HIV found that carriers of the CYP2B6*5 allele had similar efavirenz plasma concentrations compared to the *1 reference (20662624, 20841522, 22354160, 23254426, 23399569, 23990572). A study evaluating efavirenz content in hair samples among HIV patients taking efavirenz for more than three months found that the CYP2B6*5 allele did not impact long term efavirenz exposure (26655325). In human liver microsomes, decreased protein expression and/or activity was reported (11470993, 17559344). In in vitro expression systems, activity ranged from decreased (32238417, 31324697) to no change (21659470) and increased (12642465, 25897175) activity compared to the *1 reference with various substrates. Since differences in protein expression and enzyme activity observed in vitro were not reflected by meaningful differences in vivo in numerous clinical studies (20662624, 20841522, 22354160, 23254426, 23399569, 23990572, 26389554), consensus among experts was normal function based on strong evidence.