ADHD May Lead to Increased Risk of Parkinson's Disease

An early onset form of Parkinson's disease may be more likely to develop in people with attention deficit hyperactivity disorder, known as ADHD.

A team of researchers from the University of Utah studied how the two conditions might be linked. Published in Nature Neuropsychopharmacology on Wednesday, the study found that the link is even more pronounced in patients who were treated with certain drugs, such as amphetamines and psychostimulants like Ritalin.

"In individuals who were diagnosed with ADHD and weren't treated with any stimulant, there was about a two and a half fold increased in the likelihood that they would develop Parkinson's or Parkinson's related disorders," Dr. Glen Hanson, a professor of pharmacology and vice dean of the University of Utah School of Dentistry, who led the study, told Newsweek. "If they were treated with Ritalin or other amphetamines, that increased from 2.4 to 8.6-fold. There was this dramatic jump in the likelihood that they would develop a Parkinson's-like disorder."

Parkinson's disease is a neurodegenerative disease whose symptoms include rigidity, tremors and difficulty walking, and then cognitive issues at later stages of the disease, according to the Centers for Disease Control and Prevention. Scientists haven't determined the exact causes of Parkinson's but believe it could be a combination of genetic and environmental factors. In the United States each year, about 50,000 people are diagnosed with the disease.

In this study, the scientists analyzed 200,000 people with Parkinson's who were Utah residents who were born between 1950 and 1992. Of the 200,000 people, around 32,000 were diagnosed with ADHD. The researchers controlled their results for other things that might influence the development of Parkinson's. For example, people with schizophrenia might be more likely to develop the disease, and people who smoke are less likely to develop the disease. Those extremes were excluded.

Umbrella Kid ADHD
Young children dance with their umbrellas at the launch of an art installation called the Umbrella Project, which aimed to raise awareness of ADHD and autism in children. People with ADHD may be more than two times more likely to develop Parkinson’s. CHRISTOPHER FURLONG/GETTY IMAGES

A recent study found that the prevalence of ADHD in American children has increased from 6.1 percent in 1997 to 10.2 percent in 2016. During the period of Hanson's study, when its subjects were children, the prevalence of ADHD even lower than in 1997. The use of ADHD drugs has increased since that time as well.

"The use of the psychostimulants was about 15 percent," Hanson said of his study population. "In today's world, they're using the psychostimulants to treat, I would say, half to two-thirds of these patients, so our population has much fewer that were being treated with Ritalin than are being treated with Ritalin now."

These changes could mean that in the future, even more people will be diagnosed with Parkinson's than today. Hanson said, "This is like the canary in the coal mine that we're seeing the early stages that we can start asking the questions of Parkinson's disease, but we're not really to the part where the majority of Parkinson's shows up and that's after the age of 60."