Cytochrome P450 2D6 (CYP2D6), a member of the cytochrome P450 mixed-function oxidase system, is one of the most important enzymes involved in the metabolism of xenobiotics in the body. Also, many substances are bioactivated by CYP2D6 to form their active compounds. While CYP2D6 is involved in the oxidation of a wide range of substrates of all the CYPs, there is considerable variability in its expression in the liver. The gene is located near two cytochrome P450 pseudogenes on chromosome 22q13.1. Alternatively spliced transcript variants encoding different isoforms have been found for this gene.

CYP2D6 shows the largest phenotypical variability among the CYPs, largely due to genetic polymorphism. The genotype accounts for normal, reduced, and non-existent CYP2D6 function in subjects.

The CYP2D6 function in any particular subject may be described as one of the following:

A patient's CYP2D6 phenotype is often clinically determined via the administration of debrisoquine (a selective CYP2D6 substrate) and subsequent plasma concentration assay of the debrisoquine metabolite (4-hydroxydebrisoquine).

Malcolm John "Mac" Rebennack, Jr. (born November 21, 1940), better known by the stage name Dr. John (also Dr. John Creaux, or Dr. John the Night Tripper), is an American singer-songwriter, pianist and guitarist, whose music combines blues, pop, jazz as well as zydeco, boogie woogie and rock and roll.

Active as a session musician since the late 1950s, he came to wider prominence in the early 1970s with a wildly theatrical stage show inspired by medicine shows, Mardi Gras costumes and voodoo ceremonies. Rebennack has recorded over 20 albums and in 1973 scored a top-20 hit with the jaunty funk-flavored "Right Place Wrong Time", still perhaps his best-known song.

The winner of five Grammy Awards, Rebennack was inducted into the Rock and Roll Hall of Fame by singer John Legend on Monday, March 14, 2011.

Born in New Orleans, Louisiana, United States, Dr. John's Acadian ancestry traces back to the imperial territory of Alsace-Lorraine. He claims that his lineage took root in New Orleans sometime in the early 1800s. Growing up in the Third Ward, Dr. John found early musical inspiration in the minstrel tunes sung by his grandfather and a number of aunts, uncles, and cousins who played piano. He did not take music lessons before his teens, he only endured a short stint in choir before getting kicked out. His father, the owner of an appliance store and record shop, exposed him as a young boy to prominent jazz musicians like King Oliver and Louis Armstrong. Throughout his adolescence his father's connections enabled him access to the recording rooms of burgeoning rock artists such as Little Richard and Guitar Slim. From these exposures he advanced into clubs and onto the stage with varying local artists, most notably, Professor Longhair.