Summary: A new population-based study from the University of Utah Health reports that people with attention-deficit/hyperactivity disorder (ADHD) face a higher risk of developing Parkinson’s disease and related disorders. The study found that individuals with ADHD were more than twice as likely to be diagnosed with early-onset Parkinson’s (ages 21–66). The risk was particularly elevated—estimated six to eight times higher—among ADHD patients who had been prescribed stimulant medications such as methylphenidate (Ritalin, Concerta) and mixed amphetamine salts (Adderall).
Source: University of Utah Health
Overview
ADHD affects a significant portion of the population—about 11 percent of children aged 4–17 in the United States—and while its short-term effects and treatments are well studied, the long-term neurological consequences are less clear. Researchers at University of Utah Health analyzed statewide medical records and found a notable association between a history of ADHD and increased risk for diseases of the basal ganglia and cerebellum, including Parkinson’s disease. The findings were published in the journal Neuropsychopharmacology on September 12.
Key findings
- Individuals with an ADHD diagnosis were approximately 2.4 times more likely to develop Parkinson’s disease or related basal ganglia and cerebellar disorders than matched individuals without ADHD.
- Among those with ADHD who were prescribed stimulant medications (psychostimulants like methylphenidate and amphetamine salts), the risk of developing these disorders between ages 21 and 49 was markedly higher—estimated at about 8.6-fold in this study’s analyses.
- When expressed in population terms: following 100,000 adults over one year, roughly 1 to 2 people without ADHD would be expected to develop Parkinson’s disease before age 50, whereas among treated ADHD patients the estimate rises to about 8 to 9 cases per 100,000 per year.
What the study examined
The research team used the Utah Population Database (UPDB), which integrates long-standing medical and vital records for over 11 million people who have lived in Utah. They performed a retrospective cohort analysis of records spanning roughly two decades (1996–2016). Eligible subjects were born between 1950 and 1992, were at least 20 years old by the end of 2011, resided in Utah after January 1, 1996, and had no prior diagnosis of Parkinson’s disease or similar movement disorders at baseline.
The ADHD cohort included 31,769 patients, of whom 4,960 had prescriptions for stimulant medications (2,716 received amphetamine salts, 1,941 received methylphenidate, and 303 had received both types). A comparison group of 158,790 non-ADHD individuals was selected with a 5:1 match on sex and age.
Methods and controls
The analysis used time-to-event models (Cox proportional hazards models) that accounted for death as a competing risk. Researchers adjusted for sex and age and controlled for tobacco use and psychotic disorders that might independently influence Parkinson’s risk. Individuals with histories of drug or alcohol abuse were excluded. The study did not have reliable data on other potential contributors such as head trauma, certain environmental exposures, or precise duration and dose of ADHD medications.
Interpretation and limitations
Investigators caution that these results are preliminary and do not establish a direct causal link between ADHD or stimulant treatment and Parkinson’s disease. One plausible explanation is that more severe ADHD—rather than the medication itself—could be associated with higher risk of later parkinsonian disorders. Misclassification is possible if individuals in the control group were diagnosed with ADHD outside Utah or if movement disorder diagnoses were missed or recorded incorrectly. The lack of detailed medication exposure data (dosage and duration) also limits conclusions about the role of stimulant drugs.
Previous studies have reported associations between amphetamine abuse and Parkinson’s-like syndromes; this study builds on that literature but focuses on prescription use and diagnostic history in a large, population-based cohort.
Clinical perspective
Despite the observed associations, experts emphasize that stimulant medications remain an important option for many patients with ADHD, particularly children who struggle to function without treatment. Treatment decisions should be individualized, weighing benefits and potential long-term risks and considering nonpharmacologic strategies when appropriate.
Funding: The project received support from the National Institute on Drug Abuse. Additional support for the Utah Population Database was provided by the National Cancer Institute, the University of Utah’s Program in Personalized Health, the NIH Clinical and Translational Science Award program, the National Center for Research Resources, and the Utah State Department of Health.
Source and publication: University of Utah Health. The primary research article is titled “Increased risk of diseases of the basal ganglia and cerebellum in patients with a history of attention-deficit/hyperactivity disorder” and was published in Neuropsychopharmacology on September 12, 2018. The study authors include Karen Curtin, Annette E. Fleckenstein, Brooks R. Keeshin, Deborah A. Yurgelun-Todd, Perry F. Renshaw, Ken R. Smith, and Glen R. Hanson.
Abstract (summary)
ADHD is characterized by persistent inattention and/or hyperactivity and involves altered dopaminergic signaling. Common pharmacologic treatments—amphetamine and methylphenidate derivatives—affect those dopaminergic pathways. To evaluate long-term risks, researchers performed a retrospective cohort study using statewide medical records. After excluding individuals with prior movement disorder diagnoses and those with substance-abuse histories, ADHD patients (N = 31,769) were compared to 158,790 matched non-ADHD subjects. After adjustment for age, sex, tobacco use, and psychotic conditions, ADHD was associated with a 2.4-fold higher risk of diseases of the basal ganglia and cerebellum. Among the subgroup prescribed psychostimulants (N = 4,960), risk of these disorders between ages 21 and 49 was substantially higher. The authors note that elevated risk in medicated patients may reflect a more severe ADHD phenotype rather than a direct causal effect of prescribed stimulants, and they call for further research to better stratify risk and guide treatment decisions.