WASHINGTON — The number of young adults who end up in the emergency room after taking Adderall, Ritalin or other such stimulants has quadrupled in recent years, federal health officials said Thursday, fresh evidence of the unexpected consequences that can result from the wide use of medicines for conditions like attention deficit disorder.

The number of emergency room visits related to stimulants among people ages 18 to 34 increased to 23,000 in 2011, from 5,600 in 2005, according to national data from the Substance Abuse and Mental Health Services Administration, a branch of the Department of Health and Human Services. Peter J. Delany, the director of the office that oversees statistics for the administration, said the rise was particularly pronounced among 18- to 25-year-olds. He said it was part of a broader pattern of negative health effects from prescription drug abuse across American society.

Scientists have not firmly established the reasons for the rise, but Dr. Delany said one clue was the way that people who misused prescription drugs obtained them: in 2011, more than half got them at no charge from a friend or a relative, and 17 percent bought them from a friend or a relative. That suggests that a large share of the misuse is of medicines not prescribed by the abuser’s doctor.

“We have a huge issue of easy access,” said Dr. Elinore F. McCance-Katz, the chief medical officer of the substance abuse administration, adding that it applies to stimulants as well as to opioids, another category of widely abused prescription drugs.