If we give stimulant medication to a group of six children, approximately four will respond favorably. Of these four, two will have an immediate and marked improvement, while the other two will have moderate gains. Favorable responders generally have personality characteristics such as high activity levels, serious attentional problems, acceptance of social rules, and parents who support them taking medication. The other two out of six children will have neutral or negative reactions. These are most likely children under four years of age, or those with a history of tics, Tourettes syndrome, high levels of anxiety, or psychosis.