By Lauren Smith

Last updated: 05 June 2024 & medically reviewed by Morgan Blair

Schizophrenia is a lifelong mental disorder that produces hallucinations, delusions, cognitive deficits, abnormal thinking and movements, and significantly impacts patients’ lives. Substance use and schizophrenia commonly co-occur and complicate rehabilitation from addiction and recovery from psychosis.

Key takeaways:

  • Schizophrenia is associated with poor physical health, homelessness, substance abuse, victimization, and exploitation. The difficulties faced by people with schizophrenia are often exacerbated by stigma and discrimination.

  • Schizophrenia is 1.4 times more frequent among males and occurs earlier in them, with peak ages of onset between their late teens and early twenties. Peak ages of onset for women are between their late twenties and early thirties.

  • Cognitive impairments are seen in 70% of people with schizophrenia and are thought to underly the poor psychosocial outcomes of schizophrenia even more so than the positive and negative core symptoms.

Schizophrenia: Causes, Symptoms, and Diagnosis

What is schizophrenia?

Schizophrenia is a severe, long-term mental disorder characterized by psychosis, the distorted perception of reality. In schizophrenia, continuous and intermittent psychosis, delusions, disorganized thinking, and other symptoms cause disturbances in an individual’s thinking, emotions, and behavior. Schizophrenia may lead to lifelong difficulties with relationships, education, and employment, often amounting to serious disability.

Schizophrenia is associated with poor physical health, homelessness, substance abuse, victimization, and exploitation. The difficulties faced by people with schizophrenia are often exacerbated by stigma and discrimination.

The World Health Organisation (WHO) estimates the global prevalence of schizophrenia at around 0.45% of adults or one in 222 people.[1] Schizophrenia is 1.4 times more frequent among males and occurs earlier in them, with peak ages of onset between their late teens and early twenties. Peak ages of onset for women are between their late twenties and early thirties.[2]

Symptoms of schizophrenia

The symptoms of schizophrenia are divided into two primary categories: positive, the presence of symptoms not experienced by people without the condition, and negative, the absence of or deficit in normal functioning. Additionally, most people with schizophrenia also experience impairments in cognitive function.

No patient will experience all of the listed symptoms. Rather, each case has its own presentation, with a unique constellation of symptoms.

Positive symptoms

Also called psychotic symptoms, positive symptoms include:

  • Hallucinations: sensory experiences that seem real but are created by the mind. Hallucinations occur in 60 to 80% of people with schizophrenia.[3] Auditory hallucinations (“hearing voices”) are the most common but any sense (vision, hearing, smell, taste, and touch) can be involved.

  • Delusions: fixed false beliefs, maintained even in the face of contradicting evidence. Persecution delusions (that they’ll be harmed by others) or passivity delusions (that their thoughts or actions are being controlled by an external force) are common.

  • Disorganized thinking, also called thought disorders: disturbances in cognition that affect language. For instance, the speech and writing of people with schizophrenia may show incoherence (also called word salad), illogicality, derailment (moving from one topic to another, also called knight’s move thinking), echolalia (echoing another person), and clanging (alliteration, rhyming).[4]

  • Movement disorders: These include catatonia, a disorder causing immobility, mutism, staring, withdrawal, rigidity, and stereotypes (purposeless, repetitive movements). Others, including dyskinesia (involuntary muscle movements, often of the face) and parkinsonism (tremors, slow movements, rigidity, and postural instability) may occur as a result of antipsychotics but are also found in schizophrenic patients who haven’t yet taken medication.

Negative symptoms

Up to 60% of patients with schizophrenia show negative symptoms that require treatment. The frequency of the five core negative symptoms is higher among men with schizophrenia.

  • Blunted affect: displaying flat expressions and little emotion

  • Alogia: poverty of speech, reduction in the number of words spoken

  • Avolition: decreased motivation and reduced goal-directed activities

  • Asociality: lack of motivation to interact with others and form relationships; social withdrawal

  • Anhedonia: reduced ability to feel pleasure[5]

Cognitive symptoms

Cognitive impairments are seen in 70% of people with schizophrenia and are thought to underly the poor psychosocial outcomes of schizophrenia even more so than the positive and negative core symptoms.

Deficits are seen in:

  • Memory, especially verbal memory and episodic memory (memory of everyday events)

  • Attention

  • Concentration

  • Visual perception

  • Speed of processing

  • Motor skills

  • Language

  • Executive function

  • Intelligence

  • Social cognition[6]

Prodromal symptoms

By the time psychosis begins, many patients have been experiencing more subtle symptoms for around two years.[7] This earlier period is known as the prodromal stage and is estimated to affect 75% of patients with schizophrenia.[8]

Prodromal symptoms include:

  • Depression

  • Difficulty concentrating

  • Decreased motivation

  • Social withdrawal and isolation

  • Anxiety

  • Sleep disturbances

  • Neglected personal hygiene

  • Erratic behavior, change in routine

  • Suicidal ideation

  • Attenuated (lighter) psychosis: for example, magical thinking, referential delusions (the belief that ordinary events and coincidences have hidden meaning and special significance to the individual), and poorly formed hallucinations such as brief visual hallucinations or mumbled voices.[9]

Treating these patients at the prodromal stage with low doses of antipsychotics and psychosocial counseling may delay the onset of psychosis and more severe symptoms.[10] However, prodromal symptoms are often confused with symptoms of more common mental illnesses such as depression and are often identified only after schizophrenia has progressed.

How is schizophrenia diagnosed?

Schizophrenia is usually diagnosed by a psychiatrist. It requires a psychological evaluation and a complete medical exam. 

The doctor may also want to perform urine or blood tests to confirm substance abuse isn’t producing the symptoms and order imaging of the brain to exclude conditions such as brain tumors.

Other tests may include cognitive tests, personality tests, and the Rorschach (inkblot) test. As schizophrenia is linked to genetics, the doctor will want to know if anyone else in the family has experienced similar symptoms or been diagnosed with schizophrenia.

Under the DSM-5, a schizophrenia diagnosis requires:

  1. Symptoms: Two or more of the following: delusions, hallucinations, disorganized speech, disorganized or catatonic period, and negative symptoms (eg blunted affect, avolition).

  2. Social/occupational dysfunction: The condition affects at least one major area, such as work, relationships, or self-care.

  3. Duration: The main symptoms must be present for at least one month. The condition's effects must last for at least six months.[11]

Early diagnosis and treatment can significantly improve outcomes in schizophrenia.

What causes schizophrenia?

The exact cause is schizophrenia hasn’t been illuminated. It’s likely caused by an interaction of genetic and environmental factors, which may vary between cases.


The heritability of schizophrenia is estimated at 79%: that means 79% of the differences between people in the risk of developing schizophrenia is down to genes.[12] Having a first-degree relative (parent, full sibling, or child) with schizophrenia increases the risk to 7.7%.[13]

There’s no single gene that causes schizophrenia. Rather, by comparing the genomes of tens of thousands of people with and without schizophrenia, scientists have identified more than 280 locations in the genome that contribute to an individual’s overall risk.[14]

Having many of these specific genes doesn’t guarantee someone will develop schizophrenia. Rather, genes produce a vulnerability to schizophrenia, activated by environmental factors.

Environmental factors

Dozens of environmental risk factors for schizophrenia have been identified, each slightly raising the likelihood of schizophrenia, including:

  • Stressful life experiences such as abuse, bereavement, job loss, eviction, and relationship breakdown

  • Childhood adversity, including abuse, parental death or divorce, bullying, and neglect

  • Living in an urban environment doubles the risk of schizophrenia for reasons that aren’t understood but may include pollution[15]

  • Social isolation

  • Substance use, especially cannabis, associated with a two-fold increase in the risk of psychotic illness

  • Viral infections, especially herpes

  • Exposure to the parasite Toxoplasma gondii, found in cats doubles the risk

  • Complications during pregnancy, including maternal stress, nutritional deficiency, and infection[16]

What treatment options are there for schizophrenia?

Decades ago, patients with schizophrenia were typically hospitalized long-term. Today, while patients may be briefly voluntarily or involuntarily hospitalized during severe psychotic episodes, they’re typically managed within the community, with medication, psychosocial interventions, and support services.


The mainstay of schizophrenia treatment is antipsychotic medications. The first generation of antipsychotics are dopamine antagonists and block D2 receptors. A second generation, known as atypical antipsychotics, also affects the neurotransmitter serotonin.

Long-term treatment is usually required, even after psychotic symptoms subside. Some people with schizophrenia don’t believe they’re ill and fail to comply with their medication regime. These people may receive long-acting injections of antipsychotics.

Around half of patients respond well to antipsychotics, with positive symptoms minimized and social functioning improved. However, in around a third of patients, psychotic symptoms continue despite medication. They will be given the antipsychotic clozapine, which is particularly good at addressing positive symptoms and will help half of patients with treatment-resistant schizophrenia but can dangerously lower white blood cell count. Electroconvulsive therapy (ETC) may also be considered.

Antipsychotics don’t usually improve the negative symptoms or cognitive impairments of schizophrenia.

Related: borderline personality disorder

Psychosocial interventions

  • Psychotherapy: such as cognitive behavioral therapy (CBT), which teaches patients to test the reality of their thoughts, ignore hallucinations, manage symptoms, and develop better social and problem-solving skills. [17]
  • Social skills training: teaches patients communication and interpersonal skills—such as conversing with people, making friends and dating, managing their health, and engaging in leisure activities—to improve their daily functioning.

  • Family therapy: helps families to communicate better, reduce stress, and support the person with schizophrenia.

  • Vocational rehabilitation and supported employment: helps people with schizophrenia prepare for, secure, and keep jobs

Community support services

Support services can help people with schizophrenia in their daily lives, with housing, jobs, education, and crises. These services aim to promote users’ independence, community integration, and recovery and prevent relapses, hospitalizations, homelessness, and other negative outcomes.

Schizophrenia and substance abuse

People with schizophrenia are more likely to abuse drugs and alcohol than the general public. One study found that 47% of people diagnosed with schizophrenia have abused one or more substances in their lifetimes. This is 4.6 times higher than the frequency among people without schizophrenia.

The link between schizophrenia and substance abuse is complex. Some individuals with schizophrenia self-medicate with drugs or alcohol to deal with negative symptoms such as social withdrawal, dysphoria, apathy, and sleep disturbances.[18]

Substance abuse and schizophrenia may also occur independently in the same people as a result of shared genetic and environmental vulnerability factors. These common risk factors include childhood trauma, chronic stress, and poor frontal lobe function.

Related: drugs and mental health

At the same time, repeated drug use may lead to changes in the brain similar to those causing mental health conditions. Conversely, schizophrenia may make addiction more likely. It’s known to disturb dopamine and glutamate systems in the brain, which are implicated in the development and maintenance of addiction. The abnormal neurochemistry of schizophrenia may amplify the reinforcing effects of drug rewards and reduce inhibitions about drug-seeking behavior.

The most abused substances among people with schizophrenia are nicotine, cocaine, alcohol, and marijuana. The link between cannabis and psychotic illness has attracted much research and media attention in recent years. Adolescent cannabis has been found to double the risk of schizophrenia and schizophreniform disorder in adulthood.[19]

Drug use can also lead to relapse and worsened psychosis in people with schizophrenia. Substance abuse also complicates the treatment for schizophrenia and is associated with poor treatment compliance, higher hospitalization rates, and worse outcomes.

Getting help for schizophrenia

Schizophrenia can be a frightening and life-altering diagnosis. However, many people with schizophrenia respond well to medication and psychosocial interventions and hold jobs, have relationships and friends, and live independently. Early treatment significantly improves outcomes.

If you believe you or a loved one has schizophrenia you should:

  • Contact your general practitioner

  • Consults with a psychiatrist

  • Use the Substance Abuse and Mental Health Services Administration’s (SAMHSA)’s Early Serious Mental Illness Treatment Locator to find local services tailored to people experiencing their first onset of a serious mental illness

  • Call the Schizophrenia & Psychosis Action Alliance’s hotline for information and resources about schizophrenia and its treatment. The hotline is available Monday through Friday between 9 a.m. and 5 p.m. in all time zones. Dial 800-493-2094