Although two CYP2B6 alleles, *4 and *22, are categorized as increased function alleles, the effect of *4 and *22 on CYP2B6 function with respect to efavirenz plasma exposure appears to be modest based on current evidence. However, the phenotype categories of CYP2B6 rapid metabolizer (RM; one normal function allele and one increased function allele) and CYP2B6 ultra-rapid metabolizer (UM; two increased function alleles) were created to allow for the possibility that these may be clinically relevant for CYP2B6 substrates other than efavirenz. As there is no recommendation for altering dosing for CYP2B6 RMs or UMs for efavirenz, the EHR priority is sent to "normal" for these metabolizers.