Two consecutive randomized placebo-controlled two-way crossover sub-studies on amitriptyline will be conducted in consenting, healthy, male volunteers. Both sub-studies have the same aim: to determine the association between CYP2D6 genotype, drug response measured by QST and plasma concentrations of amitriptyline and its metabolites. The first sub-study will be conducted with a single high dose of amitriptyline (100 mg). The second sub-study will be conducted with repeated low doses of amitriptyline (25 mg) once a day for 10 days.