CYP2B6 (cytochrome P450 2B6) is a 491 amino acid protein encoded by the human gene CYP2B6. CYP genes are highly polymorphic and can affect individual drug response and adverse reactions to a great extent. The CYP2B6 gene product, along with a few other CYP gene products, are highly susceptible to variation due to several copy number variants (CNV), missense mutations, insertions and deletions, and gene expression mutations. There are 57 active CYP genes and 58 pseudogenes known in the human genome. In liver microsomes, CYP2B6 is involved in an NADPH-dependent electron transport pathway. It acts to oxidize a variety of structurally unrelated compounds, including steroids, fatty acids and xenobiotics. CYP2B6 is expressed in liver, lung and heart and can be induced by phenobarbital.