Psychosis (sy-KO-sis) is a broad term covering a range of mental illnesses associated with a loss of connection to reality. Illnesses that involve psychosis may severely impair a person's ability to relate to other people and to perform basic tasks of daily life.

What Is Psychosis?

Psychosis is a medical term used to describe serious mental disorders that cause a person to lose touch with reality. People with psychosis may have delusions * , hallucinations * , or dementia * ; they may lose the ability to speak coherently or to understand what others say to them; and their thoughts, feelings, and behaviors may be inappropriate and disconnected from the reality around them without their being aware of the disconnection.

Disorders associated with psychotic symptoms

In some cases, psychosis lasts only for a few days or weeks (acute or brief psychosis), but sometimes it is a chronic * condition. Some of the disorders associated with psychosis include:

Antipsychotic drugs

Antipsychotic drugs
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Medical treatment for people with psychosis improved greatly toward the end of the 20th century. Safer and more effective medications were developed. Many reforms to the laws were designed to safeguard the rights and freedoms of people with mental illnesses, so that they were no longer hospitalized against their will without a fair hearing and legal representation.

The fact that definitions of psychosis and mental illness changed over the years led to debate about whether mental illness really exists.

The astronomer Galileo Galilei (1564–1642), for example, was considered to be mentally ill because he believed that the Earth revolved around the Sun during an era in which everyone else in his culture believed the opposite. Galileo's belief threatened teachings of the Roman Catholic Church, and he was called before the Inquisition in 1633 and asked to abandon his belief. When he refused to do so, he was condemned for heresy and held under house arrest for the last nine years of his life. Galileo was not mentally ill. Galileo understood that his culture did not accept his belief, but his personal commitment to scientific reality was more important to him than acceptance by his contemporaries.

British psychiatrist R. D. Laing (1927–1989) believed that mental illness was a form of withdrawal from reality that people chose when they no longer could tolerate situations that other members of their family or society found acceptable. He thought that “mental illness” was a sane response to an insane world. Laing believed that psychiatrists sometimes diagnosed mental illness when the true problems were, in fact, rebellion and a refusal to live in an unlivable situation. Laing's publications include Sanity, Madness, and the Family; Self and Others; The Divided Self; and The Politics of Experience.

American psychologist Thomas Szasz (1920–2012) believed that mental illness is a metaphor for thoughts, feelings, and behaviors of which society disapproves. His well-known book The Myth of Mental Illness holds that society uses “mental illness” as a label to control people, forcing them to accept unwanted treatment and hospitalization. Szasz believed that all medical treatment must be voluntary.

While it is certainly true that medical diagnoses sometimes have been misused for social control, many mental health professionals do not agree with Laing and Szasz that mental illness is a myth, metaphor, or chosen response. To believe this would be to deny a biological basis for many instances of mental illness and to deny the pain, disorientation, and fear that people with mental illnesses experience.

People with psychosis are seriously ill with medical conditions that affect their thoughts, feelings, and ability to understand reality, sometimes even the reality that they need medical treatment. In fact, many patients later thank those who insisted they receive treatment, because when they recover they recognize that their illness had been affecting their thinking.

Psychosis and the Insanity Defense

The U.S. legal system rests on the notion of personal responsibility. To find a person guilty of a crime requires proof that the person committed the crime and that he or she can be found blameworthy. When might a person not be found at fault? One example is when the law allows a verdict of innocence, even when a crime has been committed, because the crime was committed in self-defense. The other extreme circumstance that might “excuse” a crime is called the insanity defense.

Psychosis is a medical term involving illnesses that cause people to lose touch with reality. Insanity is a legal term used to describe some mental states that severely limit people's ability to understand their actions so that they cannot be held responsible for those actions. Legal tests for determining sanity during court trials using the insanity defense usually focus on whether the people on trial understood what they were doing when they committed crimes, understood the difference between right and wrong, and were able to control their own behavior.

As of 2015, the legal test for insanity varied from location to location. Some states used the British M'Naghten rule, named after Daniel M'Naghten, who attempted a political assassination in England in 1843. Other states use the American Law Institute (ALI) test, also called the Model Penal Code. The ALI test was used during the 1982 trial of John Hinckley Jr., who attempted to assassinate President Ronald Reagan in 1981. When Hinckley was found “not guilty by reason of insanity,” a political backlash occurred, and the U.S. Congress introduced the legal concept of “guilty, but mentally ill.”

The American Psychiatric Association (APA), the medical group that publishes standards for classifying mental illnesses and supports research about their treatment, does not use the legal term insanity. The APA maintains that psychiatrists may testify in court to help trial participants understand mental illness and psychosis, but that questions of innocence, guilt, and moral responsibility need to be left to judges and juries.

See also Alcoholism • Alzheimer's Disease • Bipolar Disorder • Delirium • Delusions, Delusional Disorders, and Paranoia • Dementia • Depressive Disorders: Overview • Hallucination • Personality and Personality Disorders • Psychopharmacology • Schizophrenia • Seizures • Substance Abuse


Books and Articles

Arnold, Carrie. “At Risk for Psychosis?” Scientific American. August 25, 2011. (accessed November 13, 2015).

Cahalan, Susannah. Brain on Fire: My Month of Madness. New York: Simon and Schuster, 2013.

McCarthy, James B. (ed.) Psychosis in Childhood and Adolescence. New York: Routledge, 2014.


MedlinePlus. “Psychosis.” U.S. National Library of Medicine, National Institutes of Health. (accessed August 12, 2015).

NHS Choices. “Psychosis.” National Health Services. (accessed November 13, 2015).


American Academy of Psychiatry and the Law. PO Box 30, One Regency Dr., Bloomfield, CT 06002. Toll-free: 800-331-1389. Website: (accessed August 12, 2015).

American Psychiatric Association. 1000 Wilson Blvd., Suite 1825, Arlington, VA 22209. Toll-free: 703-907-7300. Website: (accessed August 12, 2015).

National Alliance on Mental Illness. 3803 N. Fairfax Dr., Suite 100, Arlington, VA 22203. Telephone: 703-524-7600. Website: (accessed August 12, 2015).

National Institute of Mental Health. Science Writing, Press, and Dissemination Branch, 6001 Executive Blvd., Room 8184, MSC 9663, Bethesda, MD 20892-9663. Toll-free: 866-615-6464. Website: (accessed August 12, 2015).

* delusions (de-LOO-zhuns) are false beliefs or judgment that remain even in the face of proof that they are not true.

* hallucinations (ha-LOO-sin-AYshuns) occur when a person sees or hears things that are not really there. Hallucinations can result from nervous system abnormalities, mental disorders, or the use of certain drugs.

* dementia (dih-MEN-sha) is a loss of mental abilities, including memory, understanding, and judgment.

* chronic (KRAH-nik) means lasting a long time or recurring frequently.

* bipolar disorder is a group of mood disorders that are characterized by alternating episodes of depression and mania.

Disclaimer:   This information is not a tool for self-diagnosis or a substitute for professional care.

(MLA 8th Edition)