The healthy volunteer brings the research medicine home and consumes it before bedtime the night before the day of the study. At eight o'clock next morning the healthy volunteer arrives to the first pupil measurement and consumption of tramadol. Tree hours later the next pupil measurement is carried through. The healthy volunteer accumulates his or her urine until 2 pm. As paroxetine is a irreversible inhibitor of the enzyme CYP2D6 there has to go at least 14 days before the next phase takes place. In that amount of time there can be recreated a new pool of enzyme.