Differential pharmacokinetics and pharmacodynamics of methylphenidate enantiomers: does chirality matter? d,l-threo-methylphenidate (MPH) is an effective first-line treatment for the symptoms associated with attention-deficit/hyperactivity disorder. << threo-methylphenidate >> inhibits the dopamine transporter and the [[ norepinephrine transporter ]], resulting in elevations of these monoamines after impulse release.