The Link Between Depression and Other Mental Illnesses

Medically Reviewed by Smitha Bhandari, MD on April 01, 2022
8 min read

Clinical depression has been linked to other mental illnesses, such as anxiety disorders, panic disorder, social phobia, and generalized anxiety disorder. Together, these conditions affect millions of Americans.

Fortunately, these disorders are treatable, and those affected can lead normal, productive lives.

Anxiety is a normal reaction to stress, but when it takes on a life of its own it becomes an unhealthy, generalized reaction that affects the body and mind. Symptoms can include rapid heartbeat, aches and pains, and muscle tension.

According to the National Institute of Mental Health, more than 18% of adults in the United States have an anxiety disorder in any given year, and anxiety disorders are prevalent in 25% of children ages 13 to 18. Like depression, anxiety is thought to arise from a combination of both genetic and environmental factors.

Although anxiety is not always present in depressive disorders, most of the time it lurks beneath the surface. But true depression differs from an anxiety disorder in that a depressed mood is typically its most obvious symptom, whereas anxiety is the primary sign of an authentic anxiety disorder.

Anxiety disorders include:

Previously, two other conditions -- obsessive-compulsive disorder (OCD) and posttraumatic stress disorder (PTSD) -- had been classified by the American Psychiatric Association as being subtypes of anxiety disorders. However, in the most recent edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), each of these conditions is now classified as its own separate type of disorder.

Anxiety disorders affect women twice as frequently as they do men. And many studies show that people with depression often experience symptoms of an anxiety disorder.

An anxiety disorder that's left untreated can cause unnecessary suffering and impairment for both the person who has one and the person's family.

People with generalized anxiety disorder (GAD) are filled with greatly exaggerated worry and tension -- even though there is usually nothing beyond ordinary concerns to worry about. These individuals anticipate disaster and ruminate about their health, their finances, their work, their relationships and family problems.

To make a diagnosis of GAD, excessive worrying and anxiety have to occur more days than not for at least 6 months. The person is unable to control the worry and may have other symptoms including:

  • Difficulty concentrating
  • Fatigue
  • Irritability
  • Muscle tension
  • Restlessness
  • Sleep disturbance

This anxiety disorder is not related to substance abuse or a medical condition. It occurs independently.

Panic disorder is another type of generalized anxiety disorder that often co-exists with depression. Panic disorder affects 6 million Americans every year, most often young adults.

Panic disorder involves the sudden onset of overwhelming fear and terror. The person may also experience:

  • Chest pain
  • Choking
  • Difficulty breathing
  • Dizziness
  • Gastrointestinal distress
  • Headache
  • Shortness of breath
  • Sweaty palms
  • Tachycardia (an unusually rapid heartbeat)
  • Trembling

The person feels like they are either going to faint, have a heart attack and die, or go crazy.

For somebody to be diagnosed with panic attack, at least four of the following symptoms need to be present:

  • Chest pain
  • Choking sensation
  • Dizziness
  • Extreme sweating
  • Fast heartbeat
  • Fear of dying
  • Feeling of losing control
  • Feelings of unreality or being detached from oneself
  • Hot flashes or chills
  • Nausea
  • Numbness
  • Shakiness
  • Shortness of breath

These symptoms are often accompanied by worry over the implications of the attack -- like fear of death from a heart attack -- and altered behavior, like avoiding a particular place because of the attack.

Specific phobias are the most common type of anxiety disorder. They involve an unreasonable or irrational fear of something that poses little or no real danger. The fear can be of a situation, object, or event. If people with phobias can't avoid what they fear, then it immediately results in a marked anxiety response. This response can include rapid heartbeat, nausea, or profuse sweating. Phobias are common and strike one out of 10 Americans, with women twice as likely to have a phobia as men.

Social anxiety disorder, also called social phobia, is a psychological condition that causes an overwhelming fear of situations that require interacting with another person or performing in front of others. Unlike being shy around strangers or nervous before a performance, social anxiety is a fear that you might humiliate yourself with your actions or speech in public.

Social phobia is common. It affects more than 15 million people in any given year. It often begins in childhood and rarely develops after age 25.

People with social phobia are often aware that their fears are irrational, but they are unable to ease or erase these fears.

The symptoms of social phobia are much the same as symptoms for other anxiety disorders. They include:

Like with other anxiety illnesses, symptoms can be tolerable or so severe that they become socially debilitating.

Schizophrenia is a type of major psychotic illness that is usually marked by an inability to distinguish the real from the imaginary, confused or jumbled thoughts, and hallucinations. Feelings of emptiness and sadness may be a symptom of the disorder, but schizophrenia and depression are different on a neurobiological level. About half of people with schizophrenia may develop a major depressive episode at some point in their lives, but depression is not considered an enduring or hallmark feature of schizophrenia. If it seems to be a major symptom, you might want to consider schizoaffective disorder as another possibility.

Eating disorders frequently occur with depression and anxiety disorders. According to the National Institute of Mental Health, eating disorders are marked by extremes. They occur when someone severely reduces food intake or overeats to the extreme. Treatment may include antidepressants.

The two most common types of eating disorders are anorexia nervosa and bulimia nervosa. Eating disorders are more common among teenage girls and women. These disorders often get worse the longer they go untreated. The lack of nutrition associated with eating disorders can harm the body's organs and, in severe cases, lead to death.

People with anorexia purposefully starve themselves, despite their hunger. They tend to excel in sports, school, and work -- often seeking perfection. Some people with anorexia stop eating in order to gain a feeling of control over their lives. Others may do so to rebel against parents and other loved ones. The diagnosis of anorexia nervosa requires that a person weigh at least 15% less than their ideal body weight. It is estimated that up to 3.7% of females will suffer from anorexia at some time during their lives.

Anorexia is primarily a food restriction disorder. However, it is not uncommon for people with anorexia to purge, or empty themselves, through vomiting and abuse of laxatives, enemas, and diuretics.

People with bulimia nervosa eat large amounts of food all at once and then vomit. The vomiting may occur multiple times during a day. The vomiting is triggered by a fear of weight gain or stomach discomfort. People with bulimia also use laxatives, diuretics, and vigorous exercise to purge themselves.

In order for a person to be diagnosed with bulimia, this behavior must occur at least twice a week for three months in a row. Although people with bulimia are often underweight, they may also have a normal body weight. It is estimated that bulimia will affect up to 4.2% of females at some point in their lives.

Substance use disorders -- which are linked to depression -- involve the use of drugs or alcohol to the point of social, financial, legal, occupational, or physical harm. Millions of Americans abuse drugs or alcohol for a variety of reasons, among them to cope with stress and anxiety. Biological factors, such as a genetic tendency, may also play a role. Substance abuse may include some of the following symptoms:

  • Continuing to use the substance despite the knowledge of its harmful effects on one's physical and mental condition
  • Finding it impossible to discontinue use despite making efforts
  • Giving up or reducing social, recreational, and work-related activities because of substance use
  • Increasing the amount of a substance used over time
  • Spending lots of time and effort either getting the substance or recovering from its use
  • Needing to increase the amounts of a substance in order to become intoxicated, or experiencing a diminished effect from continued use of the same amount.
  • Taking more of the substance to ease withdrawal symptoms
  • Withdrawal symptoms such as nausea, shaking, insomnia, agitation, hallucination, and sweating following a reduction in the amount of a substance taken

There are varied approaches to treating people with substance abuse plus depression. Some will need detoxification in a hospital or a clinic. Rehabilitation may include one-on-one counseling, group counseling, and support groups. Antidepressant medicines -- in combination with education to help people address and conquer the emotions that cause them to abuse drugs or alcohol -- can also be effective.

ADHD (attention deficit hyperactivity disorder) causes high energy and impulsive behavior. You may not be able to focus as well as you’d like. About 1 in 3 people with ADHD also have depression or have had it in the past. 

Sometimes it may be that you simply have both conditions. But in other cases, ADHD and its effects on your life are actually a cause of depression. And sometimes health care providers can misdiagnose depression in someone who simply has ADHD.

PTSD (posttraumatic stress disorder) is when you have flashbacks, nightmares, or intrusive thoughts about a terrible event that you experienced. Think of the 9/11 terror attacks or a serious car accident or an act of violence.

Many people get past such events and are able to live healthy lives. People with PTSD may remain anxious and depressed for months or years afterward. That’s part of why PTSD often happens along with substance abuse, anxiety, and clinical depression. 

Agoraphobia is an anxiety disorder that makes people more afraid than is helpful in certain situations. You might have symptoms of a panic attack like nausea with fast breathing and heart rate. It can be especially bad in situations where there’s no clear way to get away such as on public transportation or at a shopping mall. In serious cases, you might find it hard even to leave the house. Without treatment, agoraphobia can lead to depression.

Personality disorders occur in about 10% of the world’s population. Many people with these disorders don’t know they have them. There are a number of different types. With antisocial personality disorder, you may seem to disregard the needs and feelings of others. With borderline personality, you might swing wildly from one emotion to another. With narcissistic personality disorder, you may have an exaggerated sense of superiority over others. In general, you may have unstable emotions and behave impulsively, or seem to others unable to fit in. Another common factor is that you’re more likely to have a mood disorder like bipolar disorder, anxiety, or depression.