Top 5 Common Mental Illnesses in Adults

depression is real for adults
Depression, Anxiety, and ADHD are just some of the common mental illnesses found in adults.

You may not realize it, but mental illness affects many people all around us. It’s in a majority of teens, young adults, and adults.

Some know their diagnosis, but many go years and years without even knowing they have a mental illness. This is because the most common mental illnesses come in a vast array of severity. Some so subtle, they don’t even get noticed. 

Mental illnesses or mental disorders are categorized by what’s experienced in the mind and also physical symptoms.

Whether you refer to it as mental illness, mental disorder, or simply mental health, it’s fast become a common topic and is no longer such a touchy and dismissed subject.

In this top 5 article, we’re going to list the 5 most common mental health disorders in adults, go over a few symptoms, and the treatment methods of each.

What are the 5 most common mental illnesses in adults?

  1. Anxiety

Anxiety is surprisingly very common among adults and teenagers. This is mostly because there are so many forms and levels of anxiety. Anxiety disorders can develop from factors such as genetics (making it hereditary), brain chemistry, traumatic events or changes in the brain.  

Statistics from Anxiety and Depression Association of America (ADAA) show:

  • only 36.9% of anxiety disorder sufferers actually receive treatment
  • 18.1% of the US population is affected by an anxiety disorder every year
  • worldwide it’s estimated that 264 million people have an anxiety disorder.

Someone who suffers from an anxiety disorder is also likely to suffer from depression and vice-versa.

Common types of anxiety disorders include:

  • Post-traumatic stress disorder (PTSD)
  • Generalized anxiety disorder (GAD)
  • Panic Disorder (PD)
  • Agoraphobia
  • Acute Stress Disorder

Each of these has sub-categories and more in-depth information explaining what they are and how they can be treated. To learn more about them, read about each type of anxiety disorder on

  • Depression

Depression is, unfortunately, one of the most common mental illnesses in adults. For a long time, there was a stigma around depression – often times people used to disregard it as a teenage phase.

But it is not.

Depression is one of the most serious and common mental illnesses in teens and adults alike. As mentioned above, people who suffer from depression are also likely to suffer from an anxiety disorder as the two go hand-in-hand.

Depression is also a hereditary mental illness, so it can be passed down through genetics.

It is highly recommended that you get a proper check-up and diagnosis for depression if you feel you may have it. People with depression feel no sense of life motivation and can become suicidal quite quickly.

This is a serious matter, so if you’re feeling more down than usual, please make an appointment to get help.


Attention Deficit Disorder (ADD) and Attention Deficit Hyperactivity Disorder (ADHD) are another two very common mental illnesses in adults.

The two may sound similar and seem like the same thing, but they are different and are diagnosed as separate illnesses. It’s not impossible to be diagnosed with both, but it’s usually one or the other.

Common symptoms of these two illnesses include:

  • inability to concentrate
  • unable to stay still for too long
  • difficulty focusing or listening
  • short temper
  • no patience & fidgety
  • irritability and mood swings

These aren’t all the symptoms of each, just a few common ones that are recognized immediately. People who suffer from ADD and ADHD can also commonly suffer from anxiety.

Fortunately, ADD and ADHD are easily diagnosed and treatable with medication and/or therapy. A common misconception about ADD/ADHD is that you’ll grow out of it when you become an adult, but that’s not the case. These are mental illnesses that’ll be with you for life.

However, they can become much easier to manage as you get older.

  • Psychosis

According to the World Health Organization, Schizophrenia, which is the most common form of psychosis, affects almost 23 million people worldwide.

This is a very severe mental illness that if not treated correctly can affect the rest of your life. There are treatment and therapy options for psychosis, but because it affects thinking, emotions, perception, sense of self, language, and behavior; it will never fully “go away.”  

Examples of common psychotic experiences are:

Hallucinations – feeling, seeing and hearing things and voices that are not real

Delusions – fixed beliefs and an altered reality that is held firmly despite evidence to the contrary

  • Eating Disorders

An eating disorder can manifest during childhood or adulthood. This type of mental illness or mental disorder can develop from trauma (like bullying) or from having a distorted perception of self.

Research shows that eating disorders can be passed through genetics and using this information to assist with therapy is still being explored.

Examples of common eating disorders in adults are anorexia, binge eating, and bulimia. This type of mental illness can be treated with therapy programs and supervised therapy.

Eating disorders can cause long-term harm to the body and are therefore classified as very dangerous. Due to body insecurity or perhaps bullying, eating disorders are likely to be accompanied by anxiety and depression, making the case more severe.

If you know someone who is suffering from an eating disorder, please talk to them as gently as you can and encourage them to seek help.

What are the most severe mental illnesses?

The severity of mental illness is defined by the duration and disability it causes a person. Due to the nature and duration of each, the most severe mental illnesses are schizophrenia, bipolar disorder, and major depression. 

Final Thoughts

All mental illnesses should be taken seriously, no matter the severity it starts out with as symptoms of mental illnesses can change and worsen with time.

This is just an informative guideline of the top 5 common mental illnesses in adults and is by no means meant to diagnose or treat any illness you may have.

If you think you or someone you know could be suffering from these mental disorders, you or they have to get a professional diagnosis from a qualified psychiatrist.

If you or someone you know needs help, please call:

If you’re not comfortable phoning, there is an online chat option for crisis via IMALIVE.

Stay safe, you are NOT alone.

Check Out More About Mental Illness: Signs It Is Time to Get Help, Anxiety and A Toddler


  1. This is valuable information. Far too many adults that are struggling with mental illness feel alone or isolated because many of these illnesses are seen as being a teen struggle, not something you face as a grown adult, which couldn’t be further from the truth.

    • Oh yeah, it is always seen as something you will just “get over” and that is not really the case. Adults, teens, and even children can have a mental illness (or two). No one, but maybe babies, is safe from the possibility of mental health issues. It is sad but true.