Clinical effects after morphine or morphine-6-glucuronide (M6G). All spontaneous reports of side effects were noted, and their total number was counted per subject (upper parts of the table for either morphine or M6G). In addition, selected side effects were regularly rated by means of visual analog scale and the areas under the side effects ratings versus time curves (AUC) of the side effects versus time curve were calculated (lower parts for either morphine or M6G). M6G caused significantly more spontaneous reports of side effects than morphine. Men rated tiredness and drowsiness significantly lower than women. Note that the study medications had been administered in a single-blind design.