A client describes a mind that will not settle, an inability to concentrate, restlessness that makes sitting still feel intolerable, and nights spent staring at the ceiling. On the surface, this could be a generalised anxiety disorder or it could be attention-deficit/hyperactivity disorder. The symptom list barely distinguishes them, and the wrong call sends the formulation, the medication decision and the client’s self-understanding down divergent paths. ADHD and anxiety are among the most frequently confused presentations in adult mental health, and, inconveniently for us clinician, they are also among the most frequently co-occurring. Disentangling them is less about cataloguing symptoms than about understanding why a symptom is present.
In this article I will describe assessment practices that can help psychologists and psychiatrists delineate between when anxiety finishes and ADHD starts.
| Feature | Anxiety disorder | ADHD |
|---|---|---|
| Nature of the attention problem | Secondary—attention captured by worry and threat monitoring | Primary—pervasive difficulty regulating and sustaining attention |
| Present when calm and engaged? | Typically resolves; focus recovers when anxiety lifts | Persists across mood states; present even in enjoyable tasks |
| Onset | Any age; often tied to stressors or transitions | Developmental; symptoms present from childhood |
| Driver of restlessness | Autonomic hyperarousal (threat-primed) | Baseline need for stimulation and movement |
| Worry content | Threat-focused (health, relationships, catastrophe) | Often well-founded worry about lateness, deadlines, consequences of executive failure |
| Performance pattern | Worst under evaluative/high-stakes conditions; may over-prepare | Worst on tedious low-stimulation tasks; ability–output gap across contexts |
| Typical first-line response | CBT/exposure; SSRI where indicated | Stimulant medication; executive-skills and behavioural strategies |
| Relevant assessments | GAD-7, DASS-21, K10 | ASRS, ESQ-R, ACOS |
The surface overlap is substantial and genuinely difficult. Both conditions can produce restlessness and an inability to relax. Both impair concentration and working memory. Both generate a subjective sense of a racing, cluttered mind that cannot be switched off. Both disrupt sleep—anxiety through pre-sleep rumination, ADHD through delayed sleep onset and a chronically dysregulated arousal cycle. Both are associated with irritability, with procrastination and with the experience of being overwhelmed by ordinary demands. A screening instrument that taps distress, inattention or restlessness will frequently flag both, which is precisely why a positive screen opens the diagnostic question rather than closing it.
The temptation is to resolve the overlap by counting symptoms. The more productive approach is to ask what is driving each symptom—because the same observable behaviour arises from opposite mechanisms in the two conditions.
The single most useful distinction is the relationship between worry and attention. In an anxiety disorder, concentration fails because attention has been captured. The cognitive resources that would otherwise be available for a task are consumed by apprehensive expectation, threat monitoring and rumination. The attentional deficit is real, but it is downstream of the worry; remove or quieten the worry, and concentration recovers. The inattention is, in this sense, secondary and content-bound: the person is not failing to attend, they are attending intensely to the wrong thing.
In ADHD, the attentional difficulty is primary. It is not the by-product of a preoccupying worry; it is a pervasive feature of how the person’s attentional and executive systems operate. Crucially, it is present even when the person is calm, safe and engaged in something they enjoy. This is one of the most discriminating questions a clinician can ask: what happens to your concentration when you are relaxed and doing something you genuinely like? The person with an anxiety disorder will typically report that their focus is fine once the anxiety lifts. The person with ADHD will describe the same difficulties regulating and sustaining attention regardless of mood state, alongside the paradoxical hyperfocus on novel or highly stimulating material that is itself a hallmark of the condition. Attentional problems that fluctuate with anxiety point toward anxiety; attentional problems that persist across emotional states point toward ADHD.
In anxiety, motor restlessness is an expression of autonomic hyperarousal, the body primed for threat. In ADHD, it reflects a baseline need for stimulation and movement that is present whether or not the person feels apprehensive. The worry content differs accordingly. Anxiety is organised around specific or generalised threat: health, relationships, finances, catastrophic outcomes. The worry reported by adults with ADHD, when present, is frequently of a different character—well-founded apprehension about deadlines, lateness, forgotten commitments and the social and occupational consequences of executive failure.
Because ADHD is a neurodevelopmental condition, its symptoms are present from childhood—the diagnostic frameworks require evidence of onset in the developmental period, with several symptoms apparent before adolescence. Anxiety disorders, by contrast, can emerge at any age and frequently arise in response to identifiable stressors or life transitions. A careful developmental history is therefore decisive. Inattention, disorganisation and restlessness that have been continuously present since primary school, across multiple settings and independent of mood, are far more consistent with ADHD than with an anxiety disorder of recent onset.
This is also where the two conditions become causally entangled rather than merely superficially similar. Anxiety in an adult is frequently secondary to undiagnosed ADHD. Years of chronic underperformance—missed deadlines, forgotten obligations, unrealised potential, repeated negative feedback—generate a wholly rational, well-founded anticipatory worry. The person has learned, through accumulated experience, that things go wrong, and they brace accordingly. Kessler and colleagues (2006) noted in the National Comorbidity Survey Replication that because adult ADHD requires onset in childhood, the great majority of comorbid conditions are temporally secondary to the ADHD. Treating the anxiety in isolation, in such cases, addresses a symptom while leaving its engine untouched.
The performance signature differs in a clinically informative way. Anxiety, at moderate levels, can sharpen performance through heightened vigilance and effortful checking; it tends to impair performance specifically under evaluative or high-stakes conditions, where threat is most salient. The anxious student often over-prepares. ADHD-related impairment is more pervasive and less state-dependent: difficulty initiating and sustaining effort on tedious tasks, careless errors, abandoned projects and a characteristic gap between ability and output that is present across low- and high-stakes situations alike. Where the anxious client struggles most when it matters most, the ADHD client struggles most when the task is boring.
The two conditions co-occur far more often than chance, and any rigorous differential must hold open the possibility that both are present.
These figures carry a clear clinical implication: when one condition is identified, the base-rate expectation should be that the other may also be present. The diagnostic task is rarely a clean either/or.
Treatment response can retrospectively clarify an uncertain differential, provided it is interpreted cautiously. Where attentional difficulty is primarily ADHD-driven, stimulant medication typically improves concentration directly. Importantly, contrary to the common clinical assumption that stimulants must worsen anxiety, the meta-analytic evidence points the other way: Coughlin and colleagues (2015) found that psychostimulant treatment was associated with a reduced risk of anxiety in children with ADHD, consistent with the idea that improving executive function relieves the secondary, performance-based anxiety that chronic underachievement generates. Where the difficulty is primarily anxiety-driven, the appropriate first-line interventions are psychological—cognitive behavioural therapy, including exposure-based work for the relevant anxiety subtype—and, where indicated, an SSRI. A meaningful resolution of attentional complaints following anxiety-focused treatment supports an anxiety formulation; persistence of inattention once anxiety has remitted points back toward ADHD. Where both conditions are present, current guidance (Katzman et al., 2017) generally recommends treating the most impairing condition first within an integrated plan, rather than forcing a choice between them.
No self-report instrument diagnoses either condition, but a structured battery sharpens the differential and anchors it to data. For ADHD, the Adult ADHD Self-Report Scale (ASRS) screens for the symptom clusters in adults, while the Executive Skills Questionnaire–Revised (ESQ-R) profiles the executive-function domains—task initiation, sustained attention, working memory, organisation—that distinguish primary attentional dysregulation from worry-driven distraction. The ADHD Clinical Outcome Scale (ACOS) supports ongoing monitoring once a diagnosis is established.
For anxiety, the Generalised Anxiety Disorder Assessment (GAD-7) quantifies generalised worry, the Depression Anxiety Stress Scales (DASS-21) separates anxiety from depression and stress, and the Kessler Psychological Distress Scale (K10) provides a transdiagnostic distress index useful for triage. NovoPsych’s broader anxiety assessment library covers the specific subtypes. Administering measures from both families, and—critically—tracking which symptoms persist once an acute state has settled, is often what separates an anxiety formulation from an ADHD one, or reveals that both are in play.
This article is part of NovoPsych’s series on Differential Diagnosis for Mental Health Conditions. See also the related guides on Autism vs ADHD and ADHD vs PTSD/CPTSD.
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Coughlin, C. G., Cohen, S. C., Mulqueen, J. M., Ferracioli-Oda, E., Stuckelman, Z. D., & Bloch, M. H. (2015). Meta-analysis: Reduced risk of anxiety with psychostimulant treatment in children with attention-deficit/hyperactivity disorder. Journal of Child and Adolescent Psychopharmacology, 25(8), 611–617. https://doi.org/10.1089/cap.2015.0075
D'Agati, E., Curatolo, P., & Mazzone, L. (2019). Comorbidity between ADHD and anxiety disorders across the lifespan. International Journal of Psychiatry in Clinical Practice, 23(4), 238–244. https://doi.org/10.1080/13651501.2019.1628277
Katzman, M. A., Bilkey, T. S., Chokka, P. R., Fallu, A., & Klassen, L. J. (2017). Adult ADHD and comorbid disorders: Clinical implications of a dimensional approach. BMC Psychiatry, 17, 302. https://doi.org/10.1186/s12888-017-1463-3
Kessler, R. C., Adler, L., Barkley, R., Biederman, J., Conners, C. K., Demler, O., Faraone, S. V., Greenhill, L. L., Howes, M. J., Secnik, K., Spencer, T., Ustun, T. B., Walters, E. E., & Zaslavsky, A. M. (2006). The prevalence and correlates of adult ADHD in the United States: Results from the National Comorbidity Survey Replication. American Journal of Psychiatry, 163(4), 716–723. https://doi.org/10.1176/ajp.2006.163.4.716
Koyuncu, A., Ayan, T., İnce Güliyev, E., Erbilgin, S., & Deveci, E. (2022). ADHD and anxiety disorder comorbidity in children and adults: Diagnostic and therapeutic challenges. Current Psychiatry Reports, 24(2), 129–140. https://doi.org/10.1007/s11920-022-01324-5