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Autism spectrum disorder (ASD) is frequently comorbid with ADHD. Among adults with ADHD, as many as half are reported to also have ASD.

A Dutch team set out to answer two questions:

• Do adults with ADHD and comorbid ASD experience less effectiveness of pharmacological treatment for ADHD than adults with only ADHD?
• Do adults with ADHD and comorbid ASD experience different or more severe side effects of pharmacological treatment for ADHD than adults with only ADHD, as measured in side-effect scores, blood pressure, heart rate, and weight?

This was a retrospective study, using well-documented medical records, of the effects of drug treatment with methylphenidate (MPH), dexamphetamine (DEX), atomoxetine (ATX), bupropion, or modafinil.

The researchers compared 60 adults with comorbid ASD and ADHD to 226 adults with only ADHD. ADHD symptoms were scored using the Conner's ADHD Rating Scale: Self Report-Short Version (CAARS: S-S). Side effects of ADHD medication were measured using either a 13-item or 20-item checklist with 4-point scales for item response. Researchers also tracked changes in body weight, blood pressure, and heart rate.

Following treatment, ADHD symptoms among the comorbid group declined by a quarter, and among the ADHD-only group by almost a third. There was no significant difference between men and women. Controlling for age, gender, and ADHD subtype, a comorbid diagnosis of ASD also did not significantly affect ADHD symptom reduction.

Turning to side effects, in the ADHD+ASD group, there were significant increases in decreased appetite and weight loss, and decreases in agitation, anxiety, and sadness/unhappiness. In the ADHD-only group, there were significant increases in decreased appetite, weight loss, and dry mouth, and decreases in sleeping disorder, nervousness, agitation, anxiety, and sadness/unhappiness. Yet there were no significant differences between the two groups. Side effects increased and decreased similarly in both. Likewise, there were no significant differences between the groups in changes in heart rate and blood pressure. The only significant difference in medication dosage was for bupropion, which was higher in the ADHD+ASD group, though without any sign of difference in side effects.

The authors concluded that this retrospective study showed pharmacological treatment of adults with diagnoses of ADHD and ASD to be just as successful as the pharmacological treatment of adults with only ADHD, but cautioned that a randomized controlled trial should be conducted to evaluate the effectiveness and possible side effects of pharmacological treatment for ADHD in patients with ASD more reliably.

A cohort study looked at over five million adults and over 850,000 children between the ages of five and eleven who received care at Kaiser Permanente Northern California during the ten-year period from the beginning of 2007 through the end of 2016. At any given time, KPNC serves roughly four million persons. It is representative of the population of the region, except for the highest and lowest income strata.

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‍ADHD Diagnosis Rates:

• Adults: Diagnosis rates rose from 0.43% in 2007 to 0.96% in 2016.
• Children: Diagnosis rates went up from 2.96% to 3.74%, nearly four times higher than in adults.

Diagnosis Rates by Ethnicity:

• Non-Hispanic whites had the highest adult diagnosis rates, increasing from 0.67% to 1.42%.
• American Indian/Alaska Native (AIAN): Rates grew from 0.56% to 1.14%.
• Black and Hispanic adults had similar rates: Black adults increased from 0.22% to 0.69%, and Hispanic adults rose from 0.25% to 0.65%.
• Asian adults had the lowest rates (0.11% to 0.35%), followed by Native Hawaiian/Pacific Islanders (0.11% to 0.39%).

ADHD Diagnosis and Age:

The likelihood of being diagnosed with ADHD dropped sharply with age.

(When compared to 18-24-year-olds):

• 25-34-year-olds were 16% less likely.
• 35-44-year-olds were 33% less likely.
• 45-54-year-olds were less than half as likely.
• 55-64-year-olds were less than a quarter as likely.
• Adults over 65 were about 5% as likely.

This matches findings from other studies showing that ADHD diagnoses become less common with age.

‍Other Factors:

• Adults with higher education levels were twice as likely to be diagnosed as those with less education.
• Household income had little effect on diagnosis rates.
• Women were slightly less likely to be diagnosed than men.

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ADHD and Comorbidity:

Adults with ADHD were more likely to have other mental health conditions:

• Eating disorders: 5 times more likely.
• Bipolar disorder or depression: Over 4 times more likely.
• Anxiety: More than twice as likely.
• Substance abuse: Slightly more likely.

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Key Findings:

1. Rising ADHD Diagnosis Rates: The increase in diagnoses may be due to better recognition of ADHD by doctors and greater public awareness during the study period.
2. Differences by Ethnicity: The differences in diagnosis rates by ethnicity could be related to access to healthcare, cultural attitudes toward mental health, or even attempts to obtain ADHD medications for non-medical reasons, which may be more common among white patients.

Conclusion:

The authors speculate that rising rates of diagnosis “could reflect increasing recognition of ADHD in adults by physicians and other clinicians as well as growing public awareness of ADHD during the decade under study.” Turning to the notable differences by ethnicity, they note, “Racial/ethnic differences could also reflect differential rates of treatment-seeking or access to care. … Racial/ethnic background is known to play an important role in opinions on mental health services, health care utilization, and physician preferences. In addition, rates of diagnosis- seeking to obtain stimulant medication for non-medical use may be more common among white vs nonwhite patients.” They conclude, “greater consideration must be placed on cultural influences on health care seeking and delivery, along with an increased understanding of the various social, psychological, and biological differences among races/ethnicities as well as culturally sensitive approaches to identify and treat ADHD in the total population.”

The study highlights that many cases of adult ADHD go undiagnosed. Research shows about 3% of adults worldwide have ADHD, but this study found that less than 1% are diagnosed by doctors. This points to the need for better training for clinicians to recognize, diagnose, and treat ADHD in adults. It also emphasizes the importance of understanding cultural factors that affect how people seek and receive care.

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