If regarded simplistically, such a statistic might lead to the expectation that only one in five patients seen by an ADHD clinician will have the complication of an anxiety disorder.  However, such wishful thinking assumes that there is no interaction between ADHD and anxiety. Comforting as that idea might be to those who would rather have their psychopathology fit neatly into circumscribed boxes, the assumption of no interaction is NOT TRUE, with a vengeance! 

For reasons not completely understood, anxiety disorders are much more likely to occur in patients with ADHD than would be expected by chance alone.  A survey that assessed over 3000 demographically representative US respondents, aged 18 to 44, found that almost half of the respondents with ADHD also had an anxiety disorder. 2 Using the figure for nationwide prevalence cited above, this finding implies that ADHD patients are around 2 ½ times more likely than the general adult population to have an anxiety disorder.

It is not enough to simply be aware of this increased likelihood.  Even if a provider’s primary goal is to treat ADHD, a conscientious clinician will often need to actively manage anxiety disorders.  There may be no other clinician available competent to treat psychiatric comorbidities, even those as common as anxiety.  Even if there is an additional clinician to treat disorders other than ADHD, a diagnosis of ADHD will affect the approach to management of anxiety.  Two interacting psychiatric disorders are best treated by a single clinician who is aware of the complexities involved. 

Because no disorder exists in isolation, a clinical history must assess dimensions beyond the target symptoms.  Every experienced clinician has witnessed the crucial impact of the social and economic environment on disease course and prognosis.  That impact makes a good social history the indispensable component of the initial evaluation. In a similar fashion, the psychiatric history must probe for symptoms beyond or in addition to the identified problem, both because they may influence that problem, and because their effect on the patient may be as significant or even more significant than the “target” disorder.

Even if comorbidities have been stabilized before the patient's ADHD is diagnosed, their effects may be as important as those causing flagrant symptoms. As Steven Pliszka, MD asks (somewhat rhetorically) in his excellent article on the clinical implications of ADHD and anxiety, “Are the two disorders simply additive, each disorder causing separate impairment, or do they alter each other’s course?” 3 If the latter is true, even an anxiety disorder treated so effectively that symptoms are no longer present may have an important effect on a patient's ADHD.

A study of the comorbidity of anxiety and ADHD in children provides some reassurance to clinicians who are anxious about a multiplication of complexity in patients who have both disorders:  Jarrett et. al found that children with ADHD and anxiety had the same impairment on a continuous performance test as those without anxiety.4 From this data, Pliszka concludes that clinicians who encounter children with both ADHD and anxiety disorder “should view the disorders as separate, not trying to determine if one is mimicking the other,” at least in terms of their effect on attention.

On the other hand, certain studies of the interaction of anxiety and attention deficit have yielded counter-intuitive results that illustrate the complexity of the issues involved. A study which compared college students with ADHD to a control group without ADHD (and presumably without anxiety disorders,) found that anxiety increased impulsivity and decreased attentiveness in those with ADHD, but in the controls, anxiety actually improved performance on tasks requiring cognitive ability! 5

Evolutionary logic asserts that anxiety must have an adaptive value.  The improved performance in “normal” controls described above is an example of this.  The mechanism of this disruptive effect of ADHD on the beneficial aspects of anxiety would shed light on the disorder’s pathophysiology, but it remains to be elucidated.

The classic dilemma of treating comorbidities arises when an effective treatment for disease A worsens comorbid disease B.  As Pliszka points out, “there is a common clinical lore that stimulant medication will increase anxiety in those with [ADHD and anxiety].”  This supposition was partially tested by Bloch and colleagues. In those studies, to compare ADHD patients and controls, a continuous performance test was administered, with and without methylphenidate, to both groups.  The results were gratifying but perhaps not surprising:  the medication improved performance in both the ADHD and control groups.  The possibly surprising, but reassuring, finding was with regards to anxiety, which was assessed during the testing.  Anxiety was not increased by methylphenidate in the control group, and it was actually decreased by methylphenidate in the ADHD group! 6 A separate study confirmed that treating ADHD patients with a stimulant improved their anxiety as well as their ADHD symptoms.7

Despite the beneficial effects of stimulants alone on anxiety in ADHD, there are many patients for which anxiety remains a major issue even when on a therapeutic dose of stimulant. Such patients clearly deserve anxiolytic treatment to provide relief beyond that offered by their stimulant.  However, this observation does beg the question:  

Does the recommended therapeutic approach to anxiety change in the presence of ADHD? 

There is not extensive literature on this, especially for adults.  Atomoxetine (Strattera) is often suggested, as it has well-documented effectiveness for ADHD, and also for comorbid anxiety, in both youth and adults.8 There is some evidence that atomoxetine may be more effective for ADHD in patients with anxiety than in patients without that comorbidity.  

When combined with the fact that it is as effective for anxiety as SSRI’s, (at least for youth with ADHD,) atomoxetine is a rational initial ADHD pharmacotherapy for a treatment-naïve patient with significant anxiety. If such a recommendation is followed, and anxiety remains a problem, what then?  Combined treatment with stimulants and SSRI’s have been given the imprimatur of approval by academic psychiatry for this situation.9 The same authors (Krone and Newcorn) imply that for the scenario in which the patient is already on stimulant treatment for their ADHD, the addition of atomoxetine to the stimulant would be an acceptable intervention for anxiety.  

As an aside, the different permutations of clinical possibilities often call for different combinations of medications, not just in ADHD treatment, but in all of medicine.  Some of those combinations, for example, stimulant plus atomoxetine, would be censured as “therapeutic duplications” by a rigid reviewer.  However, in this example, they are all of which are expert-approved by investigators with clinical experience treating actual patients.  This situation gives us all a reminder, for the sake of the patient, to resist such rigid thinking!  

To continue in the same vein, for a psychiatric clinician to provide optimum treatment, it is necessary for her to exercise the professional privilege, granted by her intimate knowledge of the patient’s history and of the latest thinking on therapeutics, to disregard certain product labeling that is only advisory in nature.  An example of this necessity relevant to the anxiety comorbidity is that mentioned by Pallanti and Salerno in their abstract of their recent chapter titled “Adult ADHD in Anxiety Disorders.” It deserves quoting in full, both because it is good advice on important clinical issues, and because it serves as a fitting closing summary of the importance of managing anxiety AND managing ADHD:

Even if the U.S. Food and Drug Administration warns on the label of ADHD medication of the risk of increased anxiety consequent to the drug administration, some data indicate that ADHD treatment can reduce anxiety in both children and adults. Importantly, treating ADHD can help to prevent worsening of anxiety and other conditions, and improve patients’ functional outcomes.10

Resources:

1 Harvard Medical School, 2007. National Comorbidity Survey (NCS). (2017, August 21). Retrieved from https://www.hcp.med.harvard.edu/ncs/index.php. Data Table 2: 12-month prevalence DSM-IV/WMH-CIDI disorders by sex and cohort.

2 Kessler RC, Adler L, Barkley R, et al. The prevalence and correlates of adult ADHD in the United States: results from the National Comorbidity Survey Replication. Am J Psychiatry. 2006;163(4):716-723. doi:10.1176/ajp.2006.163.4.716

3 Pliszka SR. ADHD and Anxiety: Clinical Implications. Journal of Attention Disorders. 2019;23(3):203-205. doi:10.1177/1087054718817365

4 Jarrett MA, Wolff JC, Davis TE 3rd, Cowart MJ, Ollendick TH. Characteristics of Children With ADHD and Comorbid Anxiety. J Atten Disord. 2016;20(7):636-644. doi:10.1177/1087054712452914

5 Prevatt F, Dehili V, Taylor N, Marshall D. Anxiety in college students With ADHD: relationship to cognitive functioning. J Atten Disord. 2015;19(3):222-230. doi:10.1177/1087054712457037

6 Bloch Y, Aviram S, Segev A, et al. Methylphenidate Reduces State Anxiety During a Continuous Performance Test That Distinguishes Adult ADHD Patients From Controls. J Atten Disord. 2017;21(1):46-51. doi:10.1177/1087054712474949

7 In confirmation, it has been observed that addition of a stimulant to the regimen of ADHD patients improves anxiety as well as ADHD symptoms.

8 Attention-Deficit Hyperactivity Disorder in Adults and Children, edited by Lenard A. Adler, Thomas J. Spencer, Timothy E. Wilens Cambridge University Press, Jan 8, 2015

9 Krone & Newcrn

10 Pallanti, S., Salerno, L. (2020). Adult ADHD in Anxiety Disorders. In: The Burden of Adult ADHD in Comorbid Psychiatric and Neurological Disorders. Springer, Cham. https://doi.org/10.1007/978-3-030-39051-8_11