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.