Adults who started taking methylphenidate, also known as Ritalin, when they were children for attention deficit hyperactivity disorder (ADHD) may be able to lay aside concerns over whether the drug has neurotoxic effects, according to authors of an animal study published July 12 in Neurotoxicology and Teratology. In the study, scientists from the U.S. Food and Administration (FDA) used micro-PET/CT to measure the neurochemical effects of years of high doses of methylphenidate in a study in rhesus monkeys. They found that long-term use did not have a lasting impact on the function of dopamine neurons in the brain.