Medicaid beneficiaries with autism are more likely to have an ADHD diagnosis than adults in the general population.

That’s according to new research published in JAMA, which found that 33.2% of Medicaid beneficiaries with autism had an ADHD diagnosis. Comparatively, only 2.7% of the general public had an ADHD diagnosis.

Researchers found that Medicaid beneficiaries with an intellectual disability (ID) had a higher rate of ADHD diagnosis (40.2%) than those without an ID (26.7%).

While people with autism and ID were most likely to have an ADHD diagnosis, only 28% received medication for the condition. Meanwhile, 46.7% of individuals with autism but no ID received medication, and 36% of patients with ADHD but without autism had a prescription for medication.

“ADHD medication prescription rates are lower in people with ID and ADHD diagnoses regardless of the presence of autism,” authors of the study wrote. “These lower ADHD medication prescription rates could result from greater difficulty evaluating efficacy, accessing specialty care practitioners who see patients with ID, or Medicaid state-specific formulary coverage.”

Researchers also found that in every diagnostic group, patients with ADHD had a higher rate of substance use disorder (SUD), than their peers with co-occurring ADHD. Patients who received ADHD medications—both in the general population and those with autism but no intellectual disability—had lower rates of substance use disorder compared to unmedicated patients.

Study authors said these findings could help clinicians treating people with autism and ADHD in the future.

“Clinicians and service practitioners should be aware that treating ADHD may improve overall health outcomes,” authors of the study said. “Medicaid system changes to support the growing group of autistic adults with co-occurring ADHD should be targeted to ensure access to needed care, including care coordination, medication, and specialty care. Enhancing systems of care to address autistic adults’ co-occurring ADHD will likely improve their independence, health, and overall quality of life.”