For example, in AIDS clinical studies, CYP2B6 variants have been associated with 2- to 4-fold higher plasma EFV and NVP (Haas et al. 2004; Rotger et al. 2005; Rodriguez-Novoa et al. 2005; Tsuchiya et al. 2004) in HIV patients; ≥2-fold higher plasma EFV concentration is associated with neuropsychological adverse effects (Haas et al. 2004; Rotger et al. 2005; Marzolini et al. 2001; Hasse et al. 2005). Here, CYP2B6 is linked to AIDS.