Differential effects of methylphenidate on the growth of neonatal and adolescent rats.

Methylphenidate (MPH), the drug of choice in the treatment of Attention Deficit Disorders with Hyperactivity (ADD/H), has raised concern regarding its suspected potential for reducing body stature in growing patients. In a previous study we demonstrated that neonatal rats treated with MPH (35 mg/kg, SC, twice daily) showed an acute growth impairment followed by a rapid growth-rebound phenomenon. This report confirms our earlier findings in neonatal rats and extends the investigation of the growth suppressing effects of MPH to the periadolescent period of development in rats. Specifically, neonatal groups of male and female rats treated with higher and lower doses of MPH than in the original study confirmed the growth impairment and growth rebound phenomena reported earlier. Unlike neonatal rats, rats treated during the periadolescent period of development failed to show any growth impairment. These data suggest that the growth suppressing effects of MPH are the result of an acute toxicity which is readily reversible on discontinuation of the drug. Further, it is concluded that there is a low probability of long term effects on human body stature when the minimal therapeutic dose is used in clinical practice.