Methylphenidate is a CNS stimulant that is thought to block the reuptake of dopamine and noradrenaline (norepinephrine) into the presynaptic neuron. A sustained release (OROS formulation of the drug has been developed for use in children with attention deficit/hyperactivity disorder (ADHD). In children aged 6 to 12 years with ADHD, the maximum plasma concentration of OROS methylphenidate 18 to 54 mg was reached after approximately 7 to 8 hours. In adults, the plasma concentration-time profile of OROS methylphenidate differed markedly from that of the sustained release and immediate release (IR) methylphenidate formulations. In a clinical trial involving 282 children with ADHD, once daily OROS methylphenidate 18 to 54 mg was significantly more effective than placebo and demonstrated an effect similar to IR methylphenidate 5 to 15 mg 3 times daily in reducing the symptoms of ADHD. OROS methylphenidate demonstrated sustained efficacy in a 1-year noncomparative study involving children with ADHD. In clinical trials, the OROS formulation of methylphenidate had a tolerability profile similar to that of IR methylphenidate.