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.