ADHD is a neurodevelopmental condition characterized by persistent patterns of inattention and/or hyperactivity-impulsivity. Restless Legs Syndrome (RLS) is a sensory-motor disorder causing an overwhelming, uncomfortable urge to move the legs, typically during periods of rest. The observation of excessive movement and restlessness in both conditions prompts the question of whether one might cause the other.
The Nature of the Relationship
ADHD does not directly cause RLS, nor does RLS cause ADHD. The relationship is one of high co-occurrence, or comorbidity, suggesting they share common underlying risk factors. Studies consistently show that individuals diagnosed with one condition have a significantly higher likelihood of also meeting the diagnostic criteria for the other. For instance, up to 44% of people with ADHD experience RLS symptoms, while up to 26% of those with RLS also have ADHD symptoms.
This strong correlation indicates a shared vulnerability within the nervous system. One theory suggests that sleep disruption caused by RLS, which often worsens at night, results in daytime sleepiness that mimics or worsens ADHD symptoms. Another possibility is that RLS discomfort causes movement seeking relief, which may be misidentified as general ADHD hyperactivity.
Shared Underlying Biological Mechanisms
The high co-occurrence of ADHD and RLS primarily involves the dysregulation of the dopaminergic system in the brain. Dopamine is a neurotransmitter involved in movement, attention, and reward processing, and dysfunction in its signaling is implicated in the pathology of both conditions. In RLS, reduced dopamine function, particularly in the basal ganglia, contributes to the characteristic motor symptoms and the urge to move.
ADHD is also linked to differences in dopamine levels and receptor function, affecting executive functions like impulse control and attention. The shared involvement of this neurochemical pathway suggests that a common defect in the dopamine regulation loop may predispose an individual to developing both disorders. Genetics also play a role, as researchers have identified several gene variants, such as in the BTBD9 gene, associated with an increased risk for both RLS and ADHD.
A second significant biological mechanism linking the conditions is the status of iron stores, particularly in the brain. Iron is an essential co-factor for the enzyme tyrosine hydroxylase, which is necessary for dopamine synthesis. Low brain iron levels are strongly associated with RLS severity and can affect dopamine production, potentially exacerbating ADHD symptoms. Iron supplementation often alleviates RLS symptoms, highlighting the importance of iron in this shared pathology.
Distinguishing Symptoms and Diagnostic Overlap
The overlap in symptoms, especially in children, presents a diagnostic challenge, as RLS may be misinterpreted as general hyperactivity. The key difference lies in the nature and timing of the restlessness. RLS involves a distinctive sensory experience—often described as creeping, tingling, or crawling sensations in the legs—that creates an irresistible urge to move. This discomfort is typically worse during rest or inactivity, especially at night, and is immediately relieved by movement.
In contrast, ADHD hyperactivity is primarily motor and cognitive, characterized by a feeling of being “on edge” or an inability to settle, without the specific physical sensations of RLS. ADHD-related restlessness is often constant or linked to boredom, and the relief from movement is not as immediate or distinct as it is with RLS. Furthermore, RLS movements are typically focused on the legs, whereas ADHD restlessness often involves the whole body.
Treatment Considerations When Both Conditions Are Present
Treating co-occurring ADHD and RLS requires careful coordination, as treatment for one condition can potentially affect the other. Stimulant medications, commonly prescribed for ADHD, increase dopamine levels but can sometimes worsen RLS symptoms in susceptible individuals. Clinicians must carefully manage dosages and monitor for RLS exacerbation.
Treatments aimed at RLS can offer secondary benefits for ADHD symptoms. Dopamine agonists, such as ropinirole or pramipexole, are common RLS treatments that target underlying dopamine dysfunction. These medications may improve both RLS and the movement-related aspects of ADHD. If iron deficiency is identified, supplementation can significantly reduce RLS severity and potentially improve ADHD symptoms by supporting dopamine synthesis.