Connection Between Major Depressive Disorder, Anxiety, and Obsessive-Compulsive Disorder

For decades, research scientists have been attempting to tackle a fundamental question. “What are the roots of mental illness?” Throughout their search for finding an answer, they have collected a vast amount of data through genetic studies, brain activity and neuroanatomy. They have also researched the subject of comorbidity in mental health conditions.  Simply put, this is when there is more than one mental health condition or disorder occurring simultaneously in the same person.

Comorbidity within mental disorders is common.  For instance, if a person is diagnosed with both Social Anxiety Disorder and Major Depressive Disorder,  they are said to have co-existing, or comorbid, anxiety and depressive disorders.

A large, cross-sectional, national epidemiological study of comorbid conditions in mental health in Spain showed that among a sample of 7936 adult patients, about half had more than one psychiatric disorder.4 In addition, looking at the U.S. National Comorbidity Survey, 51% of patients with a diagnosis of major depression also had at least one anxiety disorder. Only 26% of them had no other mental health condition.

The following blog is in regard to three disorders that are now among the most studied in mental health.  They are anxiety, depression, and OCD (obsessive-compulsive disorder).  Before understanding how OCD, anxiety, and depression interact, we need to look at each.  Throughout the blog, when looking at causation, please notice the amount of times you see the word ‘genetic’ appear.

Major Depressive Disorder:

The American Psychiatric Association defines depression (Major Depressive Disorder, MDD) as a mood disorder that causes a substantial decrease in well-being, in regard to several different areas of life.

On an emotional level, depression brings feelings of sadness, loneliness, emptiness, a lack of pleasure or energy, and hopelessness.

On a cognitive level, depression causes detrimental beliefs that bad (negative) experiences are the person’s own fault, and that the world around them is a lonely, scary place, where things will never improve.

On an interpersonal level, depression is marked by actions and responses to others that destabilize their relationships and create problems between the person suffering from depression and those around them.

It can severely hinder their sense of self-worth, place in society, and day-to-day functioning.

Depression Demographics:   

Depression is a prevalent mental health disorder, affecting about one in 15 adults (or 6.7%) of the adult population. In the US, 17.3 million adults (7.1%) have reportedly experienced one or more depressive episodes during their lifetime.

Several risk factors have been shown to increase the chance of developing MDD. These include genetics, childhood environment, personality and temperament, later life events, and the existence of additional mental and physical disorders.


Anxiety is defined as an extreme, adverse and disproportionate concern over a possible threat. Unlike fear, which is seen as an intensely unpleasant emotion in response to perceiving or recognizing a danger or threat, anxiety is characterized by excessive uneasiness and apprehension, typically with either compulsive behavior or panic attacks.

Anxiety is a family of disorders, with a large number of individuals facing them. In the United States 19.1% of the population are diagnosed with at least one anxiety disorder, with 31.1% of US adults having dealt with an anxiety disorder sometime during their life. 

Both anxiety and depression have been associated with experiencing distress when facing the unknown, with depression related to a vague sense of mourning, and anxiety growing out of the thought of a future threat whose likelihood remains unclear.

While depression is defined by a lack of energy, anxiety is perceived as more of a system overload, and tied to excessive concern over the possibility of coming to harm.

Within the anxiety family, there are the following disorders:

  • Generalized anxiety disorder: Excessive worry over one or more major life domains (work, home, family, etc.).
  • Separation anxiety disorder: Increased distress over separating from an attachment figure (excluding relevant childhood developmental stages).
  • Panic disorder: Severe and unexpected attacks of distress, eventually fearing the onset of the next attack.
  • Social anxiety disorder: Distress over social situations that may involve scrutiny.
  • Specific phobia: Fearing certain stimuli, objects, or scenarios.
  • Selective mutism: Inability to speak in public.
  • Agoraphobia: Fear of open or enclosed spaces, using public transport, being in a crowd or outside and alone during specific situations.
  • Substance/medication-induced anxiety disorder: Symptoms of anxiety developed following use of medication or substance abuse.

Causes of Anxiety Disorder:

  • Genetics.
  • Brain chemistry.
  • Environmental stress.
  • Drug withdrawal or misuse.
  • Medical conditions.

Obsessive-Compulsive Disorder:

Obsessive-compulsive disorder, or OCD, is a mental disorder defined as a combination of anxiety-inducing mental processes and physical actions. OCD can be very time-consuming, creating significant distress, and impairing function in major life areas.

OCD is an overactive defense mechanism that repeatedly introduces anxiety into the individual’s mental health system. It consists of intrusive, obsessive thoughts that the person has very little or no control over, and then, compulsive behaviors that a person feels driven to perform in response to an obsession. Fulfilling the compulsive behaviors usually reduces a person’s distress related to an obsession.

Obsessive Thoughts: OCD-related thoughts tend to focus on one or more themes that cause the individual extreme distress. Such thoughts are intrusive, unwanted, and tend to repeat themselves in a ruminative fashion.

Compulsive Behavior: Individuals battling OCD often feel as if they are assaulted by their own mind, due to their adverse, repetitive thought patterns. As a result, many develop rituals of repeated behavior in an effort to suppress their feeling of anxiety they experience. However, while these behaviors can temporarily bring about relief, they eventually become compulsive, and in the long run, contribute to the individual’s rising levels of stress.

OCD Demographics:

2.3% of US adults and 1%-2.3% of US children and adolescents face OCD. While this disorder can start at any age, OCD symptoms usually appear between the age of ten and early adulthood. It is very hard to diagnose OCD, and is often explained away as a person’s little ‘quirks’ or peculiar behaviors.

OCD has been linked to a number of risk factors. These include genetics, environmental factors, temperament, and life events.

A Range of OCD-Related Disorders

OCD is part of a range of what is referred to in the DSM-V as OCD-related disorders. The conditions in this group involve obsessive thought patterns and unwanted actions or ceremonies meant to alleviate feelings of anxiety. They include hoarding, trichotillomania (hair-pulling), excoriation (skin picking), hoarding, and body dysmorphic disorder (a preoccupation with a perceived physical defect).  It’s important to understand the person suffering from OCD is very aware that their behaviors are not rational, but are unable to stop obsessive thoughts due to the feeling of a possible catastrophe or impending doom. 

How MDD, OCD, and Anxiety Relate to One Another:

Each of these conditions has a connection with the other two conditions ; however, in slightly different ways.

Linking OCD and Anxiety

Connecting OCD and anxiety is straightforward because anxiety is the central symptom of OCD.  It’s also the reason why OCD was, at one time, considered part of the anxiety family of disorders.

However, several crucial developments in the field of OCD research have shown that OCD needs to be separated into its own category.

One reason is that scientific discoveries have now been able to actually map out the neural pathways and structures that play a part in the development OCD.

Second, therapists in the field have noticed that specific treatments, such as cognitive-behavioral therapy, are able to offer individuals with OCD some benefit with .

Third, OCD-focused genetic research has uncovered genetic commonalities for OCD and OCD-related disorders, separating them further from other anxiety-based disorders.

How OCD and Anxiety Relate to Depression

Linking OCD to anxiety disorders is understandable because they stem from the same core symptom – anxiety. But how do either anxiety or OCD relate to depression?

One rather intuitive link between both of these anxiety-centered categories and depression is based on causation.  An individual who suffers from either OCD or anxiety may find themselves feeling hopeless, saddened or unable to enjoy life—all symptoms of depression. Facing either of these disorders for long can eventually cause them to develop depression as well.

Second, all three disorder families often appear together. Depression, anxiety, and OCD all show a high level of comorbidity with one another, with the probability of developing two or more of them together being significantly higher than chance.

Unfortunately for those facing several of these conditions at once, comorbidity decreases the chances of a symptom-free recovery when compared to those battling singular disorders.

Last, Genetics seem to shape the relationship between these three conditions. The connection appears to pass through neuroticism, which is a trait causing negative emotions. Having this personality trait may cause a person to have intense, adverse reactions to internal and external stressors, resulting in feelings of sadness, guilt and anger. Since neuroticism has been found to be both highly hereditary and a risk factor for anxiety, depression, and OCD, researchers of this characteristic have hypothesized that it acts as a mediator between all three of these conditions. 

Finally, neural structures also appear to play a part in the co-morbid development of anxiety, OCD and depression. Specifically, the amygdala portion of the brain, and its role in processing emotions, has been shown to be associated with the development of these three disorders. Damage to the amygdala has been shown to affect how we process and perceive threatening stimuli and expressions of happiness, which can result in the appearance of depression, anxiety and OCD-related symptoms. 

In conclusion, with the advent of current genetic research, we are finding studies showing that genetics and epigenetics play a role in the development of depression, anxiety, and OCD, and that there are links between each.

Other serious mental health conditions are also showing findings of a genetic role, as well as having over-lapping links to other mental health conditions.

As always, for our loved ones, we need to support mental health genetic research so we can help to end the suffering for so many.  It’s way past time for action.

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