Mental Illnesses and Disorders

The following was extracted from “Information About Mental Illness and the Brain” published by the National Institute of Mental Health. 

We can all be “sad” or “blue” at times in our lives. We have all seen movies about the madman and his crime spree, with the underlying cause of mental illness. We sometimes even make jokes about people being crazy or nuts, even though we know that we shouldn’t. We have all had some exposure to mental illness, but do we really understand it or know what it is? Many of our preconceptions are incorrect. A mental illness can be defined as a health condition that changes a person’s thinking, feelings, or behavior (or all three) and that causes the person distress and difficulty in functioning. As with many diseases, mental illness is severe in some cases and mild in others. Individuals who have a mental illness don’t necessarily look like they are sick, especially if their illness is mild. Other individuals may show more explicit symptoms such as confusion, agitation, or withdrawal. There are many different mental illnesses, including depression, schizophrenia, attention deficit hyperactivity disorder (ADHD), autism, and obsessive-compulsive disorder. Each illness alters a person’s thoughts, feelings, and/or behaviors in distinct ways. In this module, we will at times discuss mental illness in general terms and at other times, discuss specific mental illnesses. Depression, schizophrenia, and ADHD will be presented in greater detail than other mental illnesses.


Not all brain diseases are categorized as mental illnesses. Disorders such as epilepsy, Parkinson’s disease, and multiple sclerosis are brain disorders, but they are considered neurological diseases rather than mental illnesses. Interestingly, the lines between mental illnesses and these other brain or neurological disorders is blurring somewhat. As scientists continue to investigate the brains of people who have mental illnesses, they are learning that mental illness is associated with changes in the brain’s structure, chemistry, and function and that mental illness does indeed have a biological basis. This ongoing research is, in some ways, causing scientists to minimize the distinctions between mental illnesses and these other brain disorders. In this curriculum supplement, we will restrict our discussion of mental illness to those illnesses that are traditionally classified as mental illnesses, as listed in the previous paragraph.


Simply stated, mental illnesses are disorders of the brain affecting the whole person, both the body and the mind. Mental illness can affect anyone regardless of age, economic background, race and whether or not there is a family history of mental illness. There are many causes of mental illnesses such as birth trauma, chemical imbalances in the brain, and other biological, environmental, social and cultural factors.The good news is that more information is available today about the human brain than ever before. As a result, people are learning that a mental illness does not mean you are “crazy” or that you should be able to simple “snap out of it;” or, if you are experiencing a mental illness, it is not due to “personal weakness” or “a flaw in character.”


Some major mental illnesses:

  • Affective disorders, sometimes called “mood disorders,” include severe depression, mania or bipolar-depressive illnesses;

  • Schizophrenic disorders are a large group of disorders of differing origins and include such symptoms as delusions (false beliefs, despite obvious proof  to the contrary), hallucinations. (seeing or hearing things that are not present), thought disorders (manifested by disconnected speech or, in severe cases, incoherence), loss of self-identity, withdrawal from the outside world, and abnormal psychomotor activity (rocking, pacing, or immobility).

  • Anxiety disorders, although a prominent symptom of both schizophrenia and the affective disorders, in another group of disorders anxiety is the major symptom. This includes fear or anxiety that is severe or lasting such as generalize anxiety, agoraphobia and simple phobias, post-traumatic stress disorder, panic attacks, and obsessive-compulsive disorders;

  • Personality disorders such as antisocial personality, border-line personality and paranoid personality are demonstrated in individuals who have a general failure to adjust to socially acceptable norms of behavior and are incapable of establishing adequate social relationships.

Some other mental illness:

  • Dementia (such as Alzheimer’s disease);

  • Eating disorders such as bulimia and anorexia nervosa;

  • Alcohol and other drug abuse;

  • Psychoses and conduct disorders. 

If mental illness doesn’t affect you directly, it could affect someone close to you, thus affecting you indirectly. Mental illness is a treatable disease and with proper treatment, people can get well and lead productive lives.

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