The Link Between ADHD and OCD

ADHD and OCD are both common, chronic mental health conditions that are often misunderstood, stigmatized and trivialized in popular culture.

The parallels between the two conditions might run much deeper than that, though. Researchers investigating ADHD and OCD have found a number of connections between the two.

To start with, many people who live with ADHD also live with OCD, and vice-versa. ADHD is a mental health condition that tends to come with other, comorbid conditions, and one of those accompanying conditions can be OCD.

While it’s difficult to determine exactly how frequent comorbid ADHD and OCD are in the general population, one study found that 14 percent of adults with OCD had clinical levels of ADHD symptoms.

Another study found that 17 percent of adults with OCD had ADHD, and that a full 41 percent reported having had symptoms of ADHD during childhood, in many cases without receiving a diagnosis.

We know that ADHD, with or without OCD, often goes undiagnosed. When there’s a comorbid mental health condition like OCD in the picture, it may be that the comorbid condition can “overshadow” ADHD so symptoms of ADHD aren’t immediately recognized by mental health professionals.

The fact that ADHD and OCD co-occur more than you’d expect based on chance raises the question of whether there’s some underlying similarity between the two conditions. To see where that similarity might be, consider the symptoms of OCD:

• Obsessions: repeating thoughts such as fear of germs, taboo thoughts, aggressive thoughts, or a need to order things in a certain way
• Compulsions: repetitive behaviors such as cleaning, rearranging objects, checking things, or other rituals

Generally, obsessions and compulsions rise to the level of an OCD diagnosis when they are difficult to control, cause distress, or interfere significantly in someone’s life.

Symptoms of ADHD, by contrast, have to do with inattention, impulsivity and hyperactivity. Inattention includes trouble sustaining attention, distractibility, making inattentive or forgetful mistakes, procrastinating, avoiding tedious or repetitive tasks, and so on. Impulsivity and hyperactivity, meanwhile, involve symptoms such as impatience, trouble sitting still, interrupting others, and acting hurriedly without thinking through consequences.

Clearly, OCD and ADHD symptoms are different, but notice what the two conditions have in common: both involve difficulty controlling one’s thoughts and behaviors.

The ability to self-regulate one’s own brain, or to exercise top-down control over what one’s brain does, is a set of skills that psychologists call executive functions.

In ADHD, deficits in this area show up when people struggle to control where their attention is directed in an intentional, top-down way, or when they fail to inhibit or delay impulsive actions.

But OCD symptoms can also be seen in terms of executive functioning deficits. Struggling to free one’s self from intrusive thoughts is, in a way, an inability to direct one’s attention in the desired direction. And engaging in compulsions involves not being able to override an unwanted behavior.

From that perspective, it makes sense that differences in brain regions involved in executive functioning have been tied to both compulsive symptoms of OCD and impulsive symptoms of ADHD.

Similarly, adults with ADHD and adults with OCD tend to have impairments in their ability to switch attention from one task to another. That research finding led the study’s authors to suggest that “attention switching problems may reflect both symptom overlap and a common etiological factor” between the two conditions.

To put it another way, difficulty regulating one’s attention, thoughts, and actions in a top-down manner might contribute to both ADHD and OCD symptoms.

In fact, some researchers have even challenged the idea that ADHD and OCD are distinct conditions, suggesting that there may be more variation within the two diagnoses than between them. However, ADHD and OCD remain classified as separate conditions in the DSM, and despite the areas of overlap between the two, researchers have also found some neurocognitive differences that are specific to each of them.

The similarities between ADHD and OCD raise another interesting question: are the underlying genetics between ADHD and OCD also similar?

Answering that question is tentative, considering how much we still have to learn about the genetics of ADHD. That said, one research project involving scientists from institutions such as UC San Francisco, Harvard Medical School and Johns Hopkins found several areas of overlap between genes related to ADHD and OCD symptoms.

That discovery led the researchers to conclude that some genetic risk factors for ADHD and OCD “transcend traditional diagnostic boundaries,” possibly because they represent “an underlying vulnerability” such as “failure of top-down cognitive control.”

Another study found that people with OCD were more likely to have relatives with combined ADHD and Tourette’s Syndrome, meaning genes in common between OCD and ADHD could play a role in Tourette’s as well. Research from psychiatrists at Harvard Medical School and Yale School of Medicine has likewise backed up the idea that Tourette’s is related to genetic risk for both ADHD and OCD.

Besides possibly sharing some underlying biological causes, symptoms of ADHD and OCD might interact in complicated ways.

For example, adults with OCD who also have ADHD tend to report an earlier age of onset of OCD, with more obsessions and compulsions. And accompanying ADHD has been linked to a higher risk of hoarding among both children and adults with OCD.

Studies like these highlight the need to make sure that both ADHD and OCD are treated when they occur together. The good news for people with ADHD and OCD is that symptoms of both conditions can be managed, and working with a mental health professional can make a profound difference in how the conditions impact one’s life.