Adults diagnosed with ADHD and those who take psychostimulants are more likely to develop Parkinson’s-like disorders.
Adults diagnosed with attention deficit hyperactivity disorder (ADHD), as well as adults who were prescribed psychostimulant medications for ADHD, have higher incidences of early-onset Parkinson’s and Parkinson’s-like diseases.
That’s according to a study published this week in the journal Neuropsychopharmacology.
Parkinson’s disease is a neurological movement disorder that is typically diagnosed in patients ages 60 or older.
It occurs when neurons in the brain die and therefore are not producing dopamine, which controls movement in the body.
Common symptoms of Parkinson’s include uncontrollable tremors and changes to voice and handwriting.
Parkinson’s cannot be cured, so treatment focuses on managing the symptoms.
“We don’t know that much about underlying mechanisms of Parkinson’s,” said Dr. Glen Hanson, professor of pharmacology and toxicology at the School of Dentistry at the University of Utah and a senior author of the new research.
“In terms of mental health diseases, I’m not aware of any disease that has been linked to Parkinson’s” until now, he added.
Parkinson’s has some known environmental causes, such as chemical exposure, and is believed to occur from a combination of genetic and environmental factors.
ADHD, on the other hand, is a mental health disorder that causes impulsive behaviors.
It can range from mild to severe. Both adults and children can be diagnosed.
ADHD often presents as predominantly inattentive, or predominantly hyperactive, meaning patients often struggle with concentration or often have an overabundance of energy.
These symptoms are typically treated with prescription amphetamines (stimulants) that regulate dopamine and norepinephrine in the brain.
The retrospective study data was culled from medical records in the Utah Population Database between 1996 and 2011. It looked at 31,769 individuals who had been diagnosed with ADHD or other hyperactivity disorders.
Of the ADHD patients, 4,960 had been prescribed psychostimulants, such as Ritalin or Adderall. The researchers also examined 158,790 people without an ADHD diagnosis. Comparison for the study matched the ADHD cohort and the non-ADHD cohort by their age and sex.
They found that individuals with ADHD were more than twice as likely to develop early-onset Parkinson’s or Parkinson’s-like diseases.
Not only that, but the ADHD patients who had been prescribed psychostimulant medications had an increased risk of developing Parkinson’s by sixfold to eightfold.
The authors believe the study is the first to link a disorder diagnosed in childhood to a neurodegenerative disorder in later life.
“Really long-term health effects of having ADHD may be under-studied at this point,” said Karen Curtin, PhD, MStat, associate director of the Utah Population Database.
She noted that ADHD did not start being used as a diagnosis until the 1970s.
“So it’s probably about time to start looking at these later-life effects,” she told Healthline.
The researchers sought to build upon their previous research that had also found higher incidences of Parkinson’s in people who abused methamphetamines (meth), an illegal type of amphetamines.
Both amphetamines and meth release dopamine in the brain, which provides an energy boost.
The previous study about meth and Parkinson’s was published January 2015 in the journal Drug and Alcohol Dependence.
The researchers found that the group who had used meth and amphetamines had a threefold risk of developing Parkinson’s disease.
It examined a batch of medical records between 1996 and 2011. It divided the cohorts into a group who used meth or amphetamine-type stimulants, a group who used cocaine, and a group who did not use drugs or alcohol.
At the time, “it came up, ‘well, stimulants are [also] used to treat ADHD patients and would that predispose ADHD patients to have these longer-term health consequences?'” said Curtin.
That spurred researchers to turn their attention to prescriptive amphetamines, which, Curtin noted, are a “much lower dose” than the amphetamines in meth.
This most recent study in Neuropsychopharmacology found higher incidences of early-onset Parkinson’s in ADHD patients who took both methylphenidate (Ritalin or Concerta) and mixed amphetamine salts (Adderall).
That is particularly interesting, Curtin said, because the two medications are “chemically different from a pharmacology standpoint,” but have similar long-term effects on ADHD patients’ brains.
“We wouldn’t necessarily expect to see the same association in both,” she said.
ADHD is one of the most widely diagnosed disorders in children, with nearly 1 out of 10 kids in the United States having the ailment.
According to data from the Centers for Disease Control and Prevention (CDC), approximately 9 percent of children ages 2 to 17 had an ADHD diagnosis in 2016, and 62 percent of children diagnosed with ADHD were taking medication for it.
Currently, the American Academy of Pediatrics advises medications for ADHD and/or behavior therapy for children and adolescents ages 6 to 18.
Researchers are aware that parents whose children take psychostimulants to treat childhood ADHD may be worried by their findings. But they cautioned that more information is needed before drawing any conclusions.
Any possible link between ADHD patients and use of psychostimulant medications with Parkinson’s disease is “not causation… We don’t know that the relationship we observed is caused by the [ADHD] treatment,” Curtin said. “It would take further study.”
“Children being treated today are at low risk of developing Parkinson’s early, because it’s just not very prevalent in the general population,” she explained. “But I would like to see some resources come this way to study it more and for other groups to kind of start looking at this question and these long-term effects.”
Curtin added, “I don’t want anyone out there to panic, because as a parent myself, I could imagine this type of finding having me a little bit concerned.”
Hanson agreed that the benefits of having a child’s ADHD under control with psychostimulants still outweighs a Parkinson’s-related risk that may unfold in the future.
But in the hypothetical case that there is a strong link between psychostimulants and Parkinson’s, ADHD medications will have to adapt.
“If it’s the drug that’s making the ADHD linked to Parkinson’s worse, then we really need to look at our pharmacology and see if we can’t find a substitute that isn’t doing this,” he said. “So if that’s what we figure out is the case, then we need to go back to the drawing board, come up with some different drugs.”
The research is a good jumping off point to “ask some causative questions,” he continued. “What is it about the dopamine system in an ADHD patient that lends itself to a deterioration into Parkinson’s when they get older?”
There are so many different explanations to consider.
“It could be the people that end up being prescribed for ADHD, their condition is just more severe, and it’s the more severe ADHD itself that is predisposing the brain to Parkinson’s-like disorders,” said Curtin. “I don’t want to, at this point, blame the medication [for the development of Parkinson’s].”
The researchers also noted the limitations of their data.
Curtin pointed out how they did not contact patients individually, and therefore they don’t have dosage or compliance information — in other words, whether ADHD patients actually took the psychostimulants that they were prescribed and how much they took.
Researchers simply knew that these patients had been prescribed those meds, according to their medical records.
“This was just a first pass at what, in the population, we could observe,” said Curtin.
Most importantly, she wants other researchers to see if these findings can be replicated.
“I would hope that other groups that have access to large databases might be able to do a similar data study and see if they confirm these findings, and if they don’t confirm them, what were the differences in their population versus ours,” she said. “There’s definitely a lot more work to do.”