The Top Five Most Common Mental Illnesses

The number of individuals experiencing mental illness around the world continues to grow. Characterized by what people experience in their minds, but sometimes involving physical symptoms, and their emotional well-being, the cause of many mental health disorders is yet to be discovered. Many of the symptoms are scientifically understood, however.

Below you’ll find a high-level overview of the most common mental illnesses as well as common treatments. The list is by no means exhaustive but is meant to be a guide to frequently occurring conditions, some of which can present simultaneously.


Impacting an estimated 300 million people, depression is the most common mental disorder and generally affects women more often than men. It is often characterized by loss of interest or pleasure, general sadness, feelings of guilt or low self-worth, difficulty falling asleep, eating pattern changes, exhaustion and a lack of concentration. Depression doesn’t just arise as a result of “too much” or “too few” brain chemicals, specifically serotonin, as it is often depicted. Rather, several forces such as genetics, life events, medical problems and medications can bring the illness on.

Because depression can present as both long-lasting or as recurring, depression can severely interfere with a person’s ability to function at work or school and can hurt relationships. At its most severe state, depression can lead to suicidal thoughts and actions. To effectively treat depression in some cases, cognitive behaviour therapy, psychotherapy and antidepressant medication can be valuable.


It is not uncommon for a person experiencing depression to also have anxiety (and vice versa), a disorder that affects 40 million adults in the U.S., or 18.1 percent of the population, every year. Anxiety disorders develop from a multitude of factors, including genetics, brain chemistry and life events, and while it is a highly treatable illness, only 36.9 percent of those who live with anxiety actually seek out treatment, and ultimately, access it. Psychotherapy and medication play an important role in helping to control and manage the symptoms of anxiety.

Bipolar Affective Disorder

Engendering both manic and depressive episodes, sometimes book-ended, and sometimes featuring moments of “normal” or stabilized mood, this illness impacts approximately 60 million people worldwide. Manic episodes can contain elevated or irritable mood, hyperactivity, inflated self-esteem and a lack of desire to sleep. Hypomania is a less severe form of mania. Depressive episodes are often characterized by feelings of extreme sadness, hopelessness, little energy, and trouble sleeping. While the cause of bipolar is not entirely known, a mixture of genetic, neurochemical and environmental factors can play a role in the progression of the illness, which can be treated through medication and psychosocial support.

Schizophrenia and Other Psychoses

Psychoses, including schizophrenia, is a severe mental illness impacting about 23 million people worldwide and is characterized by distortions in thinking, perception, emotions, sense of self, and behaviour. Those who have these illnesses can experience hallucinations and delusions starting in late adolescence or early adulthood, making it difficult for people to work, study, or interact socially. Due to stigma and discrimination, many who experience these mental illnesses do not have access to adequate health and social support (sometimes leading to housing insecurity), which could help treat the disorder.


Dementia is generally chronic or progressive in nature and entails a deterioration of cognitive function beyond normal ageing, impacting about 50 million people across the globe. From memory, orientation and thinking, to comprehension, calculation, and language, the decline in cognitive function is generally met with deterioration in emotional and social control. Dementia is caused by a variety of diseases that impact the brain, and there is currently no cure available, but there are palliative treatments designed to ease the suffering and confusion of the sufferer.

Mental health illnesses are a global issue that touches nearly every person in some way — and these are just a few of the most commonly documented. While every situation is unique, there are treatment and recovery options available to help an individual achieve strength and support. Taking the time to recognize your symptoms and get an accurate diagnosis can help best determine the most appropriate treatment — be it be pharmaceutical intervention or a treatment plan involving psychotherapy with a licensed therapist.