CYP2B6*37 (c.516G>T, p.Q172H/splice defect; c.548T>G, p.V183G; c.785A>G, p.K262R) – Decreased function: CYB2B6*37 is assigned decreased function. CYP2B6*37 contains c.516G>T which causes aberrant splicing (see CYP2B6*6 for more information) (23418033). Multiple in vitro studies using cDNA expression systems found that CYP2B6*37 has no enzyme activity with bupropion and efavirenz compared to the *1 reference (23418033, 30201214). However, there was no in vivo data or data for liver microsomes. As is the same for *6, the mechanism for decreased activity is aberrant splicing caused by c.516G>T, which leads to reduced amounts of protein and thus, activity (14551287, 18171905, 24260284). As a result, alleles having c.516G>T are considered decreased function, regardless of the functional status of additional other variants unless these cause no function (e.g., CYP2B6*13 and CYP2B6*38). Therefore, the consensus among experts was decreased function based on the presence of c.516G>T and limited evidence.