OCD vs ADHD: Differences and Similarities

Obsessive-Compulsive Disorder (OCD) and Attention Deficit Hyperactivity Disorder (ADHD) are two mental health conditions commonly occurring in children. About 25% of patients with OCD are also diagnosed with ADHD, although these two disorders are considered to lie on opposite ends of the impulsive-compulsive behavioural spectrum. Why is this? Read on to find out more about the symptoms of OCD vs ADHD, causes of OCD vs ADHD, and treatments of OCD vs ADHD.
Klara Hatinova

Klara Hatinova

Klara is postgraduate researcher in experimental psychology at the
University of Oxford.

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What is the key difference between OCD and ADHD?

OCD is a psychiatric disorder characterised by compulsivity, whereas ADHD is characterised by impulsivity. Nonetheless, these symptoms are often misdiagnosed among clinicians.

Let us compare the symptoms of the two diseases more closely.

Symptoms: OCD vs ADHD

Obsessions and Compulsions in OCD

OCD, as the name implies, is characterised by two primary symptoms: obsessions and compulsions. Obsessions are repeating, upsetting, and unwanted thoughts that can manifest in various ways. For example, a strong fear of acquiring infections or contamination, thoughts of harming someone else, unwanted sexual or religious thoughts, or intense urges to make things orderly, symmetrical, or predictable [2, 3].

Compulsions are specific behaviours that individuals with OCD feel forced to perform to relieve the anxiety created by obsessive thoughts. Compulsions are, therefore, the symptom of OCD that is recognised and creates alarm. Compulsions may look like extreme or excessive cleaning, counting rituals, precise organising or arranging of objects, frequent checking and re-checking, and specific cleaning or washing rituals, such as washing your hands or scrubbing a surface a certain number of times [2, 4].

Inattention, Hyperactivity, and Impulsivity in ADHD

ADHD is a condition that was traditionally found to affect primarily children, but we now know up to 6% of adults also experience ADHD [5]. ADHD presents through inattention, hyperactivity, or impulsivity, where individuals can experience a spectrum of all three symptoms.

Inattention in ADHD manifests as difficulty focusing or concentrating on tasks. Individuals may be forgetful about completing tasks and can be easily distracted. They may make frequent mistakes or miss details when studying or working. They may find it hard to maintain focus when listening, reading, or holding a conversation and have trouble organising their daily tasks. Losing items frequently and being easily distracted by small things happening around them are also common symptoms of inattention [6, 7].

Hyperactivity in ADHD is typically characterised by difficulty sitting still, excessive talking, and an inability to carry out tasks quietly. People with ADHD may interrupt others when speaking, playing, or doing tasks; they may also fidget, squirm in their seats, and frequently get up from their seats - essentially always "on the go" [6, 7]. Hyperactivity symptoms are the first to be noticed in children but are more manageable in adults. This is why ADHD in adults is under-reported [5].

Impulsivity in ADHD can present as difficulty with impulse control, interrupting people while they’re talking or working, talking excessively, being impatient, or finding it difficult to wait your turn. People with ADHD may blurt out answers before questions are completed and have trouble waiting their turn [6, 7, 8].

A perhaps surprising symptom of ADHD is ADHD fatigue.

Additional Symptoms in ADHD

In addition to these core symptoms, people with ADHD may also experience executive dysfunction, which refers to difficulties in absorbing or remembering new information, ignoring distractions, regulating emotions and behaviours, and switching between tasks or decision-making. ADHD individuals can also have co-occurring tics, anxiety disorders or learning disabilities, which can exacerbate the symptoms of ADHD [9, 6, 8]. ADHD paralysis is another symptom that can occur in ADHD patients.

ADHD may also come with symptoms which are a bit surprising. For example, research indicates that there is a significant link between hypermobility and ADHD. Another interesting fact is that ADHD may cause difficulties with eye contact.

Causes: OCD vs ADHD

OCD and ADHD are both complex conditions with multiple potential causes, most of which are still not fully clear. The most prominent factors contributing to the causes of both OCD and ADHD include:

Genetic Factors

The primary evidence for the role of genetics in OCD and ADHD is that if you have a close relative with OCD or ADHD, your chance of developing this condition is increased [10, 11].

Glutamate transporters have a demonstrated link to OCD genetics, but other candidate genes, like serotonin and dopamine systems, have not been replicated [4, 3, 11].

On the other hand, genetics are likely to play a more significant role in ADHD, as the heritability of ADHD was shown to be up to 75% [10]. Specific gene associations have been found in dopamine and noradrenalin neurotransmitter systems, but again, the findings are not consistent. Modern genetic studies, including Genome-wide association studies (GWAS), demonstrated the linkage of 37 specific sections of the human DNA to ADHD risk [10, 12].

Brain Structure and Function

Brain structure and function are also implicated in both OCD and ADHD. Both OCD and ADHD are common in children, indicating that neurodevelopmental processes may contribute to the pathology. The most consistent finding when comparing OCD and ADHD neurobiology is an alteration in the cortico-striatal network. Differences in the volume of the basal ganglia, the striatal component of the cortico-striatal network, have been identified in OCD and ADHD. Changes to the excitation and inhibition within this extensive brain network can explain compulsive and disinhibited impulsive behaviour [9]. Overactivation leads to compulsive, OCD-like behaviour, whereas suppression leads to impulsive, ADHD-like behaviour.

At a smaller scale level, changes to dopamine are characteristic of ADHD, whereas serotonin changes are more likely to be seen in OCD [9]. Both dopamine and serotonin are critical neurotransmitters in modulating the cortico-striatal network.

Environmental Factors

Environmental factors can also increase your chances of developing both OCD and ADHD, although systematic investigation of environmental risk factors is complicated to piece apart from genetic factors [13].

Environmental risk factors for OCD include stress at home, school, work, or in personal relationships, personality traits like neuroticism, childhood abuse, and traumatic brain injury [14, 11].

Pre-natal and early-life environmental factors have a more significant role in ADHD than in OCD [7]. For example, prenatal exposure to the neurotoxin methylmercury also increases the risk of developing ADHD due to the effect of methylmercury on the dopaminergic system [15].

Treatments: OCD vs ADHD

There are several treatments available to manage symptoms of OCD and ADHD.

Medications

For both OCD and ADHD, medications play a significant role in treatment. In the case of OCD, the primary medications include certain types of antidepressants, specifically Selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine (Prozac) or sertraline (Zoloft). If these don't work, tricyclic antidepressants that act on noradrenalin and dopamine can also be used, as well as sedative drugs [16, 17].

Researchers have been investigating the effectiveness of Ketamine for OCD , but ketamine treatmend for OCD is still lacking FDA approval.

ADHD is primarily treated with stimulant medications. Among these, Adderall, Concerta, and Ritalin are the most commonly prescribed. These drugs work by increasing the amount of dopamine and norepinephrine, reducing fatigue and improving focus [18, 19]. The use of antidepressants for ADHD like Zoloft, Prozac, or Lexapro is generally not recommended.

Cognitive Behavioral Therapy (CBT) for OCD vs ADHD

Cognitive Behavioral Therapy (CBT) is a standard treatment for OCD, with lower efficacy in ADHD. For OCD, CBT uses Exposure and Response Prevention (ERP), which involves gradually exposing you to your fears or obsessions and teaching you healthy ways to deal with the anxiety the obsessions may cause [16].

In contrast, for ADHD, CBT is rarely used, and the standardised guidelines are scarce. CBT is more often used in adults and acts to improve individuals' ability to manage their impulsive behaviours [20].

Alternative and Experimental Treatments for OCD vs ADHD

For severe OCD that does not improve with pharmacological of CBT treatments, repetitive transcranial magnetic stimulation (rTMS) is an experimental therapy that has shown benefits in reducing OCD symptoms [21]. rTMS is a brain stimulation procedure that uses magnetic waves to target specific brain areas associated with OCD, mainly the frontal brain areas.

Supplementary treatment for ADHD includes education and training for parents, giving them the skills and strategies to help their child. For school-aged children, school support is critical. School support could include classroom-based behavioural interventions, such as learning to manage impulsions, fidget toys, or safe spaces. Focusing on organisation skills is another essential management tool for childhood ADHD [7].

Experimental treatments for ADHD include viloxazine, a non-stimulant medication without evidence of drug dependence, which has previously been used as an antidepressant. In April 2021, viloxazine was approved by the US Food and Drug Administration (FDA) for the treatment of ADHD in children. The previous use of viloxazine as an antidepressant has shown it is safe, and new clinical trials have supplemented its safety with beneficial effects on reducing ADHD symptoms [22].

Healthy Lifestyle to Manage OCD vs ADHD

In individuals with ADHD, living a healthy lifestyle, including healthy eating and regular exercise, may also help manage symptoms. Other lifestyle adjustments may include daily physical activity, eating a balanced diet, getting plenty of sleep, limiting screen time, and practising mindfulness meditation or yoga [6, 8]. All of these aspects improve the management of hyperactivity and reduce impulsive thoughts.

Similarly, in OCD, lifestyle adjustments of stress management and body-mind interventions, like yoga, have demonstrated subtle improvements in quality of life when carried out alongside standard treatment [23].

To summarise, it's essential to see that OCD and ADHD are distinct disorders which present differently depending on the individual. OCD and ADHD are often misdiagnosed due to the compulsive-impulsive behavioural traits and overwhelming anxiety caused by OCD thoughts. Nonetheless, an accurate diagnosis is critical, as treatment strategies are distinct and incorrect treatment may exacerbate symptoms of OCD or ADHD.

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Klara Hatinova

Klara Hatinova

Klara is a postgraduate researcher in experimental psychology at the University of Oxford. She has worked across a spectrum of hot topics in neuroscience, including her current project measuring reinforcement learning strategies in Parkinson’s disease. Previously, she studied the efficacy of psilocybin as a therapy for critical mental health conditions and examined molecular circadian rhythms of migraine disorders. She completed her undergraduate degree in Neuroscience at the University of Glasgow and participated in a year abroad at the University of California, where she worked on a clinical trial for spinal cord injury.