Tramadol is an interesting drug. For some people it relieves pain and for others has no effect. The reason is that there is a universe of patients who are unable to metabolize tramadol. This is because of a variation in the cytochrome 450 (CYP 450) enzyme superfamily, particularly the isoform CYP2D6. These enzymes are responsible for enzymatic drug metabolism. For those with a genetic deficiency of this isoform tramadol does not work to relieve pain.