CYP2B6*2 (c.64C>T, p.R22C) - Normal function: CYP2B6*2 is assigned normal function based on in vivo (heterozygous patients) and in vitro studies. Multiple studies evaluating efavirenz plasma concentrations among patients with HIV found that CYP2B6*2 heterozygotes had similar efavirenz plasma concentrations compared to the *1 reference (21896912, 22471906, 23254426, 23399569). A study evaluating efavirenz content in hair samples among HIV patients taking efavirenz for more than three months, similarly found that CYP2B6*2 did not impact long term efavirenz exposure (26655325). Additionally, one in vitro study using human liver microsomes (17559344) and two in vitro studies using cDNA expression systems (12642465, 30201214) found that CYP2B6*2 had similar enzyme activity compared to the *1 reference. Therefore, consensus among experts was normal function based on strong evidence.