Patients are often stigmatized by lack of public understanding about schizophrenia. The disease is often confused with split personalities (dissociative identity disorder, DID), but they are different disorders. DID, which is rare, is characterized by the presence of two or more alternate personalities in one body, each having their own memories, behavior and relationships. Patients with schizophrenia may have strange and unpredictable behavior, but they do not have more than one personality.

Nor should schizophrenia be confused with two similarly named conditions: schizoid personality disorder (marked by withdrawn, solitary and emotionally detached behavior) or schizotypal personality disorder (marked by widespread social deficits and eccentric behaviors).

Another misperception about schizophrenia is that patients are violent. However, most people with schizophrenia are not prone to violence and often prefer to be left alone. Studies have demonstrated that if patients do not have a criminal record or substance abuse problem prior to developing schizophrenia, they are unlikely to commit crimes after becoming ill. Patients with paranoid schizophrenia are more likely to commit an act of violence, which is usually directed at a someone close to them or someone about whom they have delusions.

People with schizophrenia do abuse alcohol and drugs more frequently than the general population. However, most scientists do not believe that substance abuse causes schizophrenia. Also, some people who abuse drugs exhibit symptoms similar to those of schizophrenia, and patients are sometimes mistakenly thought to be under the influence of drugs. Drugs can also make the symptoms of schizophrenia worse, both directly because of the effect of the drug on the brain and secondarily because people who are using illegal drugs frequently do not take their medication as they should.

Nicotine is the most common form of substance abuse among patients with schizophrenia. Research has shown that people with schizophrenia are addicted to nicotine at three times the rate of the general population (75 to 90 percent versus 25 to 30 percent), according to National Institute of Mental Health (NIMH).