Top 11 Most Common Mental Health Illnesses

  • Time to read: 8 min.

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Mental health illnesses are more common than you might think. In fact, according to the National Alliance on Mental Illness (NAMI), approximately one in five adults in the United States experiences a mental health illness in a given year. That’s about 43.8 million people!

Mental health illnesses can be very serious and even life-threatening, so it’s important to be aware of them and know how to get help if you or someone you know is struggling. In this article, we will introduce you to the eleven most common mental health illnesses.

Anxiety Disorders

Anxiety disorders are the most common type of mental health illness, affecting 40 million adults in the United States, or 18.1% of the population.

There are many different types of anxiety disorders; however two of the most common are generalized anxiety disorder and panic disorder.

Generalized Anxiety Disorder (GAD)

This is characterized by persistent and excessive worry about a number of different things. People with GAD may have a hard time controlling their worry and may feel anxious about anything and everything.

Symptoms of GAD include:

  • Excessive worry
  • Restlessness
  • Fatigue
  • Difficulty concentrating
  • Irritability
  • Muscle tension
  • Sleep problems

Panic Disorder

This is characterized by recurrent and unexpected panic attacks. A panic attack is a sudden period of intense fear or discomfort that can include a racing heart, shortness of breath, chest pain, or dizziness. People with panic disorder may live in fear of having another attack and may avoid places or situations where they think an attack could happen.

Symptoms of panic disorder include recurrent and unexpected panic attacks, as well as:

  • Fear of dying
  • Heart palpitations
  • Sweating
  • Shaking or trembling
  • Shortness of breath
  • Sensations of choking or smothering

Behavioral and Emotional Disorders in Children

Behavioral and Emotional Disorders in Children

There are many different behavioral and emotional disorders that can affect children. Some of the most common are attention-deficit/hyperactivity disorder (ADHD), conduct disorder, and oppositional defiant disorder (ODD).

Attention-deficit/Hyperactivity Disorder (ADHD)

This is characterized by problems with focus, hyperactivity, and impulsivity. Children with ADHD may have difficulty paying attention in school or following instructions. They may also be very active and have a hard time sitting still.

Conduct Disorder

This is characterized by a persistent pattern of disruptive and aggressive behavior. Children with conduct disorder may fight with other children, bully others, or break rules at home and at school. They may also have a hard time following rules and may be disrespectful to authority figures.

Oppositional Defiant Disorder (ODD)

This is characterized by a pattern of negativistic, defiant, and hostile behavior toward authority figures. Children with ODD may argue with adults, refuse to comply with rules, deliberately annoy others, and blame others for their own mistakes.

Bipolar Affective Disorder

Another common mental health illness is bipolar affective disorder, also known as manic-depressive illness. Bipolar disorder is characterized by extreme changes in mood, energy, and activity levels. People with bipolar disorder may swing from feeling overly happy and energized (known as mania) to feeling very down and depressed (known as depression).

In addition, people with bipolar disorder may also experience many different symptoms, including:

  • Changes in sleep patterns
  • Changes in appetite
  • Agitation or restlessness
  • Irritability or anger
  • Loss of interest

While bipolar disorder can occur at any age, it is most commonly diagnosed in young adulthood.


Many people often lump depression and anxiety together, but they are two very different things. Depression is characterized by persistent feelings of sadness and hopelessness. People with depression may also experience a loss of interest in activities they once enjoyed, changes in sleep and appetite, fatigue, and difficulty concentrating.

Depression is one of the most common mental health illnesses, affecting millions of people around the world. It is important to remember that depression is a real illness and not just a “case of the blues.” If you are feeling depressed, it is important to talk to your doctor or a mental health professional.

While there are many different types of depression, some of the most common are:

  • Major depressive disorder
  • Dysthymic disorder
  • Seasonal affective disorder
  • Bipolar disorder
  • Premenstrual dysphoric disorder

Dissociation and Dissociative Disorders

Dissociation and Dissociative Disorders

Dissociation is a mental process where a person disconnects from their thoughts, feelings, memories, or sense of self. Dissociation can be a normal response to a traumatic or stressful event. However, for some people, dissociation can become a chronic problem that can interfere with their daily lives.

Dissociative disorders are characterized by chronic dissociation. These disorders can cause a person to feel disconnected from their own thoughts, feelings, and identity. Dissociative disorders often occur as a result of trauma, such as child abuse or neglect.

The most common dissociative disorder is dissociative identity disorder (DID), formerly known as multiple personality disorder. DID is characterized by the presence of two or more distinct personalities, each with its own pattern of thinking, feeling, and behaving. People with DID often have gaps in their memory, which can make it difficult to recall certain events or periods of time.

Eating Disorders

Eating disorders are characterized by a preoccupation with food and weight. People with eating disorders may try to control their weight by starving themselves, overeating, purging, or using laxatives. Eating disorders are serious mental illnesses that can lead to dangerous health problems, such as malnutrition, organ damage, and even death.

Anorexia nervosa, bulimia nervosa, and binge eating disorder are some of the most common eating disorders.

Anorexia nervosa is characterized by self-starvation and an intense fear of gaining weight. Bulimia nervosa is characterized by binge eating followed by purging (via vomiting, excessive exercise, or the use of laxatives). Binge eating disorder is characterized by recurrent episodes of binge eating, but without the purging behaviors seen in bulimia nervosa.

Post-Traumatic Stress Disorder

Post-traumatic stress disorder (PTSD) is a mental illness that can occur after a person has experienced or witnessed a traumatic event, such as a natural disaster, a car accident, or a terrorist attack. PTSD is characterized by symptoms such as flashbacks, nightmares, and severe anxiety. People with PTSD or PTSD attacks may also feel detached or numb.

PTSD is a serious mental illness that can have a profound effect on a person’s life. If you think you may be suffering from PTSD, it is important to seek professional help.

There are many different types of therapy that can be effective in treating PTSD, such as cognitive-behavioral therapy, exposure therapy, and eye movement desensitization and reprocessing (EMDR).

Obsessive Compulsive Disorder

Obsessive Compulsive Disorder

Obsessive compulsive disorder (OCD) is a mental illness characterized by obsessions (recurrent, unwanted thoughts) and compulsions (repetitive behaviors or mental acts that a person feels compelled to perform). People with OCD often have obsessive thoughts about germs, contamination, and dirt. They may feel the need to wash their hands repeatedly or avoid touching things that they believe are contaminated.

When people think of OCD symptoms, they often think of hand-washing or cleaning. However, OCD can involve any type of obsession or compulsion. For example, some people with OCD may have obsessive thoughts about violence or harm. They may feel the need to check on loved ones frequently to make sure they are safe.

OCD can be a debilitating mental illness, but it is treatable. The most common treatment for OCD is exposure and response prevention (ERP), which involves gradually exposing a person to their fears and helping them to resist the urge to engage in compulsive behaviors.


Paranoia is a mental illness characterized by paranoid thoughts and delusions of persecution or grandeur. People with paranoia may believe that they are being followed, spied on, or plotted against. They may also believe that they are superior to others or have special powers or abilities.

Paranoia is a serious mental illness that can lead to social isolation and anxiety. It’s also different than having a phobia. For example, someone with a phobia of spiders may avoid going outside because they’re afraid of encountering a spider. But, someone with paranoia may believe that the government is tracking their every move, so they may avoid going outside altogether.


Psychosis is a mental illness characterized by psychotic symptoms, such as hallucinations and delusions. Hallucinations are false or distorted perceptions of reality, such as hearing voices or seeing things that are not there. Delusions are false beliefs, such as the belief that one is being followed or persecuted.

Psychosis is a serious mental illness that can be debilitating. It can cause people to withdraw from friends and family, and it can make it difficult to function in everyday life. If you think you may be experiencing psychosis, it is important to seek professional help.


The final mental illness on our list is schizophrenia, which is one of the more well-known mental illnesses. Schizophrenia is a chronic, severe, and disabling brain disorder. Someone with schizophrenia may experience hallucinations (seeing or hearing things that are not there), delusions (false beliefs), and disordered thinking.

While people who have schizophrenia may seem like they have lost touch with reality, it is important to remember that they are not dangerous. People with schizophrenia are more likely to be the victims, rather than the perpetrators, of violence.


Mental illness is a serious issue, and it is important to seek professional help if you think you may be suffering from a mental illness or if you know someone who is. Mental illness is treatable, and there are many resources available to help people who are struggling.

If you or someone you know is in need of help, please don’t hesitate to reach out for assistance. There are many people who care and are ready to help.

FAQ – Mental Health Illnesses

Why do people get mental health illnesses?

The causes of mental illness are varied and complex. It is important to remember that there is not one single cause for mental illness. Rather, it is the result of a combination of biological, psychological, and social factors.

What are the most common mental health illnesses?

The most common mental health illnesses are anxiety disorders, mood disorders, eating disorders, and substance abuse disorders.

What are anxiety disorders?

Anxiety disorders are the most common type of mental illness. They are characterized by feelings of fear, worry, and anxiety. Common examples of anxiety disorders include generalized anxiety disorder, panic disorder, and social anxiety disorder.

What are mood disorders?

Mood disorders are characterized by changes in mood. Common examples of mood disorders include depression, bipolar disorder, and seasonal affective disorder.

What are eating disorders?

Eating disorders are characterized by abnormal eating habits. Common examples of eating disorders include anorexia nervosa, bulimia nervosa, and binge eating disorder.

What are substance abuse disorders?

Substance abuse disorders are characterized by the abuse of drugs or alcohol. Common examples of substance abuse disorders include alcoholism and drug addiction.

What is something interesting about mental health illnesses that is not well known?

Mental health illnesses are often misunderstood. This can lead to stigma and discrimination against those who suffer from mental illness. It is important to remember that mental illness is not a choice and that people who suffer from mental illness are not weak or crazy. Mental illness is a real and serious medical condition that should be treated with compassion and understanding.