CYP2B6*31 (c.937C>A, p.L313I) – Normal function: CYP2B6*31 is assigned normal function. A study evaluating efavirenz content in hair samples among patients with HIV taking efavirenz for more than three months found CYP2B6*31 did not impact long term efavirenz content (26655325). An in vitro study using a cDNA expression system similarly found CYP2B6*31 demonstrated similar enzyme activity compared to the *1 reference (30201214). Therefore, consensus among experts was normal function based on limited evidence.