OCD and ADHD can look similar at the surface and are often confused with each other, particularly in adults. They are also genuinely co-occurring more often than chance, and many people meet criteria for both. This article covers how to tell them apart, what the co-occurrence evidence shows, and how treatment is shaped when both are present.
What OCD is
Obsessive-compulsive disorder is a condition characterised by recurrent intrusive thoughts, images or urges (obsessions) and repetitive behaviours or mental acts performed in response to those obsessions (compulsions) [1]. The pattern causes significant distress or impairment and takes more than an hour a day for most people meeting criteria. NICE CG31 sets out the UK clinical approach to OCD and body dysmorphic disorder [2].
Common obsessions include fears of contamination, fears of harm coming to oneself or others, intrusive sexual or violent thoughts, and concerns about symmetry or "just right" feelings. Common compulsions include washing, checking, counting, ordering and mental rituals. The compulsions reduce the distress temporarily but reinforce the underlying anxiety, which is part of the cycle that maintains the disorder.
OCD affects around 1 to 2 percent of the adult population at any given time.
How often OCD and ADHD co-occur
Studies have found elevated rates of OCD in samples of children and adults with ADHD, and elevated rates of ADHD in samples with OCD. The figures vary [4, 5]:
- Among children and adolescents with OCD, around 10 to 30 percent meet criteria for ADHD
- Among adults with OCD, around 10 to 15 percent meet criteria for ADHD
- The reverse co-occurrence (ADHD samples meeting OCD criteria) is also elevated above the general population, with estimates in clinical samples typically around 5 to 15 percent
The Geller et al. 2004 work and subsequent studies have suggested that the OCD-ADHD co-occurrence is a clinically meaningful subgroup with its own treatment implications [4]. The Brem et al. 2014 review covered the neurobiological link, including shared involvement of frontostriatal circuits and the partial overlap in genetic risk factors [5].
Why the two can be confused
Several features look similar at the surface but have different underlying mechanisms:
Repetitive checking
A person with OCD checks because of an obsessional fear (have I locked the door, have I turned off the oven, have I made a mistake at work). The checking is driven by anxiety about a specific feared outcome and is felt as a need that must be addressed.
A person with ADHD checks because of forgetfulness, working memory difficulty, or genuine uncertainty about whether they completed the task. The checking is driven by knowing that they often do not remember whether they did something. The underlying mechanism is different even where the behaviour looks identical.
Mental rumination
OCD rumination is intrusive, distressing, and felt as ego-dystonic (the person experiences the thoughts as unwanted and not "themselves"). The content is usually focused on specific themes that touch on the person's deepest fears.
ADHD-related rumination is more often replaying social interactions, work mistakes, or recent events. It is distressing but less specifically themed and is more often experienced as part of the person's ordinary thought stream, just amplified.
Perfectionism
ADHD perfectionism is often about not finishing because nothing feels "good enough" yet, with the perfectionism functioning as a form of avoidance.
OCD perfectionism is about not stopping because a specific standard has not been met, with the perfectionism driven by an obsessional fear of being wrong or making a mistake.
Restricted or repetitive behaviours
ADHD repetitive behaviours (foot tapping, fidgeting) are driven by under-stimulation and serve a self-regulatory function.
OCD compulsions are driven by anxiety reduction and serve to reduce the distress caused by obsessions.
The clinical distinction often becomes clearer with a structured interview and time. Self-report screening tools can over-detect either condition in the presence of the other.
How treatment is shaped when both are present
NICE CG31 sets out the UK approach to OCD [2]. NICE NG87 covers ADHD [3]. The combination produces a few practical principles:
Treat the most impairing condition first or in parallel
OCD that is causing significant distress and functional impairment usually warrants prompt treatment. CBT with exposure and response prevention (ERP) is the first-line psychological treatment under NICE CG31, with SSRIs as the first-line medication option in moderate to severe OCD or where psychological therapy is declined or insufficient [2].
ADHD treatment is sequenced around the OCD picture. Where stimulants are appropriate, they are usually compatible with SSRIs at standard doses, although the prescriber checks for specific interactions.
Watch for stimulants worsening OCD
A small subgroup of patients with co-occurring OCD and ADHD find that stimulants worsen the OCD picture (more intrusive thoughts, more compulsive behaviour). This is not common but does happen. Where it does, formulation changes, dose adjustment, or a switch to a non-stimulant (atomoxetine or guanfacine) are considered.
CBT with ERP for OCD
The evidence base for CBT with ERP in OCD is mature [2]. Delivery by a clinician with OCD-specific training is more effective than generic CBT. The presence of ADHD does not change the recommendation; ADHD-aware adjustments to the therapy structure (between-session reminders, structured homework, more frequent contact) can improve engagement.
Address the broader anxiety picture
Co-occurring anxiety is common in both OCD and ADHD. The full picture often includes generalised anxiety, social anxiety or panic. Treating each strand is more effective than focusing on one.
Co-occurring autism is worth considering
Some autistic features (insistence on sameness, repetitive behaviours, rigid thinking) can look like OCD at the surface. Where the developmental history shows autistic features, autism assessment may be useful in addition to OCD assessment.
What this means in practice
- OCD affects around 1 to 2 percent of adults; co-occurrence with ADHD is elevated, with around 10 to 30 percent of children with OCD also meeting ADHD criteria.
- The two can look similar at the surface (checking, rumination, perfectionism, repetitive behaviours) but have different underlying mechanisms.
- Structured clinical assessment is the most reliable way to distinguish them; self-report tools can over-detect either in the presence of the other.
- Treatment usually addresses both. CBT with ERP and SSRIs are the first-line options for OCD under NICE CG31; ADHD treatment continues alongside.
- A small subgroup find that stimulants worsen OCD; switching formulation or to a non-stimulant is the usual response.
When to speak to a professional
Speak to your GP if obsessions and compulsions are taking more than an hour a day or are causing significant distress, particularly if ADHD-type difficulties are also present. NHS routes for both conditions exist; Right to Choose in England applies to ADHD. NeuroFX offers private ADHD assessment for adults and children aged 6 and upwards with co-occurring OCD considered. The OCD-UK charity has UK-specific resources at ocduk.org. Seek urgent help via 111, 999 or A&E for any acute mental health crisis, including intrusive thoughts of self-harm.
Sources
- American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR). Washington, DC: American Psychiatric Association Publishing; 2022.
- NICE. Obsessive-compulsive disorder and body dysmorphic disorder: treatment. CG31. National Institute for Health and Care Excellence. https://www.nice.org.uk/guidance/cg31
- NICE. Attention deficit hyperactivity disorder: diagnosis and management. NG87. National Institute for Health and Care Excellence. https://www.nice.org.uk/guidance/ng87
- Geller DA, Biederman J, Faraone S, et al. Re-examining comorbidity of Obsessive Compulsive and Attention-Deficit Hyperactivity Disorder using an empirically derived taxonomy. European Child and Adolescent Psychiatry. 2004;13(2):83-91.
- Brem S, Grünblatt E, Drechsler R, Riederer P, Walitza S. The neurobiological link between OCD and ADHD: a systematic review and meta-analysis. Attention Deficit and Hyperactivity Disorders. 2014;6(3):175-202.
