NAMI HelpLine

 

 

Schizophrenia is a serious mental illness that can interfere with a person’s ability to think clearly, manage emotions, make decisions and relate to others. It is frequently a complex, long-term medical illness. The exact prevalence of schizophrenia is difficult to measure. However, previous estimates for schizophrenia and related psychosis disorders ranged from 0.25% to 0.64% of U.S. adults, with a newer estimate for schizophrenia spectrum conditions at 1.2% of U.S. adults. Although schizophrenia can occur at any age, the average age of onset tends to be in the late teens to the early 20s for men, and the late 20s to early 30s for women. It is uncommon for schizophrenia to be diagnosed in a person younger than 12 or older than 40. It’s important to be aware that with early diagnosis and treatment, it is possible to live well with schizophrenia.

Causes

Research suggests that schizophrenia may have a combination of possible causes, some of which include:

  • Genetics. Schizophrenia isn’t caused by just one genetic variation, but a complex interplay of genetics and environmental influences. Heredity does play a strong role — your likelihood of developing schizophrenia is more than 6 times higher if you have a close relative, such as a parent or sibling, with the disorder. It’s important to know that most people who have a first degree relative (parent or sibling) with schizophrenia will not develop the condition.
  • Environment. Exposure to viruses or malnutrition before birth, particularly in the first and second trimesters, has been shown to increase the risk of schizophrenia.  These environmental stressors are thought to activate genetic risks; this process and is called epigenetics. Recent research also suggests a relationship between autoimmune disorders and the development of psychosis.
  • Brain chemistry. Problems with certain brain chemicals, including neurotransmitters called dopamine and glutamate, may contribute to schizophrenia. Neurotransmitters allow brain cells to communicate with each other. Networks of neurons are likely involved as well.
  • Substance use. Some studies have suggested that taking mind-altering drugs during teen years and young adulthood can increase the risk of schizophrenia. A growing body of evidence indicates that smoking marijuana increases the risk of psychotic incidents and the risk of ongoing psychotic experiences. The younger a person is and the more frequently they use marijuana, the greater the risk.

Related Conditions

People with schizophrenia may have additional illnesses. These may include:

Successfully treating schizophrenia often improves these related illnesses. And successful treatment of substance misuse, PTSD or OCD usually improves the symptoms of schizophrenia. These co-occurring diagnoses require a more tailored treatment plan so be sure to ask your health care provider about how multiple conditions can be addressed.

 

Reviewed and updated December 2025

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