ADHD is tied to an increased risk of Parkinson’s disease, with the new-found link even much stronger when Ritalin and other medications are used to treat attention-deficit hyperactivity disorder, suggests a study published Wednesday in the journal Neuropsychopharmacology.

About 11 percent of children across the U.S. have been diagnosed with ADHD, but until now little research has been conducted into the long-term health effects of the disorder and medication used to treat it, WebMD reported.

Researchers at University of Utah Health conducted an extensive review of data and found that ADHD patients had an increased risk of developing early onset Parkinson's and Parkinson-like disease.

"Parkinson's disease is commonly thought of as a neurodegenerative disease associated with aging," said Glen Hanson, senior author on the paper, in a statement to Science Daily. "This may be the first time where a childhood disease and its treatment may be linked to a geriatric expression of neurodegenerative disorder."

Over two million children in the U.S. have ADHD, the Learning Disabilities Association of America reported. Parkinson's affects about one million people in the U.S., according to the Parkinson’s Foundation.

The U.S. Centers for Disease Control and Prevention reported that children over six years were recommended medication to treat the disorder. However, according to the study, the estimated risk of developing Parkinson's was six to eight-times higher for ADHD patients prescribed the stimulant medications, including methylphenidate (Ritalin, Concerta, Daytrana, Metadate and Methylin), mixed amphetamine salts (Adderall) and dexmethylphenidate (Focalin).

To determine these findings, researchers reviewed the Utah Population Database (UPDB), which contains medical records of more than 11 million individuals who have lived in the state, and honed in on people who had no prior diagnosis of Parkinson's or Parkinson-like diseases.

Next, they analyzed the ADHD population, consisting of 31,769 patients, of which 4,960 were prescribed stimulant medications, and concluded that patients with a more severe type of ADHD may be at an increased risk of developing motor neuron diseases like Parkinson's.

The study suggests this may be a result of medication however, further studies are needed to establish a more definitive conclusion.

"The jury is still out," said Karen Curtin, a study author. "The increased risk we observed in people could be linked to having ADHD itself or perhaps a more severe form of ADHD, which may be more likely to be treated with medications."