Schizophrenia is a chronic mental disorder classified under the schizophrenia spectrum and other primary psychotic disorders. It primarily disrupts how a person perceives reality, thinks, and relates to others. The condition affects roughly 1 in 345 people worldwide, with onset most common in late adolescence and the twenties, typically appearing earlier in men than in women.
A Psychotic Disorder, Not a Personality Disorder
Schizophrenia is sometimes confused with dissociative identity disorder or personality disorders, but it belongs to an entirely different category. Its defining feature is psychosis: a disconnection from shared reality that can include hearing voices, holding fixed false beliefs, or having severely disorganized thinking. The international classification system groups it under “Schizophrenia Spectrum and Other Primary Psychotic Disorders,” with “primary” meaning the psychosis isn’t caused by drug use, a medical condition, or another psychiatric disorder like bipolar disorder.
For a formal diagnosis, a person must show at least two core symptoms for a significant portion of a one-month period, and continuous signs of disturbance must persist for at least six months. At least one of those symptoms has to be hallucinations, delusions, or disorganized speech. There also needs to be a noticeable decline in the person’s ability to work, maintain relationships, or care for themselves.
Three Categories of Symptoms
Schizophrenia symptoms fall into three domains: positive, negative, and cognitive. These categories describe different ways the disorder disrupts normal functioning.
Positive Symptoms
Positive symptoms are experiences added on top of normal perception. Hallucinations are the most recognizable: hearing voices that aren’t there, or less commonly, seeing, feeling, or smelling things that don’t exist. Delusions are fixed beliefs that persist despite clear evidence against them, such as believing you’re being surveilled or that you have a special identity. Disorganized behavior can look like unpredictable emotional reactions, strange movements, or actions that seem purposeless to others.
Negative Symptoms
Negative symptoms are the opposite. They represent things that are taken away: emotional expression flattens, motivation drops, speech becomes sparse, and the ability to feel pleasure diminishes. These symptoms are often less dramatic than hallucinations but can be more disabling in daily life, making it hard to hold a job, maintain friendships, or keep up with basic routines.
Cognitive Symptoms
The cognitive domain was recognized more recently and includes problems with attention, working memory, and the ability to plan or organize. A person might struggle to follow a conversation, make decisions, or use information they just learned. These difficulties aren’t captured by the other two categories but play a significant role in how well someone can function independently.
What Happens in the Brain
The oldest and most well-known explanation centers on dopamine. In simplified terms, too much dopamine activity in certain brain circuits appears to drive the positive symptoms like hallucinations and delusions, while too little dopamine reaching the frontal parts of the brain contributes to negative symptoms like flat emotion and low motivation. This is why most medications for schizophrenia work by dialing down dopamine signaling.
A newer theory focuses on a different brain chemical, glutamate, which is the brain’s primary excitatory messenger. In this model, certain glutamate receptors aren’t working properly, and this dysfunction ultimately throws dopamine levels off balance in ways that produce both positive and negative symptoms. This hypothesis helps explain why dopamine-targeting medications don’t fully resolve all symptoms, particularly the cognitive and negative ones.
Genetics and Risk Factors
Schizophrenia is highly heritable. A large Danish twin study estimated heritability at 79%, meaning that the majority of variation in who develops the disorder is explained by genetic factors. If one identical twin has schizophrenia, the other has about a 33% chance of developing it too, compared to 7% for non-identical twins. That 33% figure is important: it’s high enough to confirm a strong genetic component, but low enough to prove that genes alone don’t determine the outcome. Environmental factors, prenatal exposures, childhood adversity, and other stressors also play a role.
Having a first-degree relative with schizophrenia raises your risk substantially compared to the general population, but most people with a family history never develop the condition.
How It’s Treated
Treatment combines medication with psychosocial support. The primary medications are antipsychotics, which come in two generations. First-generation antipsychotics work by blocking dopamine receptors directly. Second-generation antipsychotics, starting with clozapine, affect a broader range of brain chemicals and tend to have a different side-effect profile, though both generations carry risks including weight gain and metabolic changes.
Medication alone isn’t sufficient for most people. Cognitive behavioral therapy can help individuals challenge delusional thinking and develop coping strategies. Cognitive remediation targets the memory and attention problems that medications largely don’t address. Social skills training, vocational rehabilitation, and family-based interventions all improve long-term functioning. The combination of medication and these psychosocial approaches produces better outcomes than either one alone.
Physical Health and Life Expectancy
One of the most concerning aspects of schizophrenia is its impact on physical health. A Swedish national study found that men with schizophrenia died an average of 15 years earlier than the general population, and women died 12 years earlier. These gaps were not explained by suicide or accidents alone. The leading causes of death were heart disease and cancer, the same conditions that kill most people, just earlier and with less prior diagnosis.
People with schizophrenia who died of heart disease were far less likely to have been previously diagnosed with it (26% compared to 44% in the general population), suggesting their physical symptoms were underrecognized or undertreated. Diabetes was roughly twice as common among people with schizophrenia, and rates of chronic lung disease and pneumonia were also more than double. Some of this stems from medication side effects, some from lifestyle factors related to the illness itself, and some from the reality that people with severe mental illness often receive less thorough medical care.