Researchers found that young people who take stimulants such as methylphenidate (Ritalin, Concerta) and Adderall have lower bone density than their peers. This could have serious consequences later in life, the study suggests. "Adolescence and young adulthood are critically important times for accruing peak bone mass -- the largest and densest bone," said the study's lead investigator, Dr. Alexis Feuer, a pediatric endocrinologist at Weill Cornell Medicine in New York City.