The federal agency says it is updating drug labels to include information about priapism, a condition that can permanently damage a patient's penis.
The stimulant, methylphenidate (meth-ihl-PHEN'-ih-dayt), is found in treatments including Ritalin, Concerta and Daytrana.
ADHD is a common childhood disorder that hampers a child's ability to pay attention and control behaviour.
The FDA says the median age of patients taking methylphenidate who had priapism was 12 and a half years old.
The FDA says people should talk to their doctors before halting the drugs. Parents should talk to boys taking the drug so they are aware of warning signs.