Low dose tricyclic antidepressant drugs are routinely administered co-analgesics in pain medicine. Amitriptyline is largely considered as a gold standard. Amitriptyline underlies cytochrome CYP2D6 and CYP2D19 metabolism. CYP2D6 is highly polymorphic; numerous genetic variants result in 4 major classes characterizing enzymatic activity: poor metabolizers, intermediate metabolizers, extensive metabolizers and ultrarapid metabolizers. It is not known to which extent metabolizer classes determine pain outcomes or side-effects. As only one in three pain patients is considered to be a responder to amitriptyline's co-analgesic effect, prediction of treatment efficacy with a fast and easy to perform bedside test may contribute to the patients quality of life. The aim of this study is to determine the influence of cytochrome variants on experimental pain, drug related side-effects and finally identification of active metabolites.