The diagnosis of any mental health disorder represents a serious condition. Most clinicians consider the most severe of all the psychiatric diagnoses listed by the American Psychiatric Association to be schizophrenia. Schizophrenia is a heterogeneous disorder that consists of a number of very serious symptoms. It is not a disorder of having multiple personalities as still believed by some; that diagnosis was formally termed multiple personality disorder but is now known as a dissociative identity disorder.

Schizophrenia is a psychotic disorder, and it is one of the first categories of mental illnesses to be identified. The actual term schizophrenia comes from the psychiatrist Eugene Bleuler in 1911 who envisioned schizophrenia as the splitting of one’s thinking abilities from their personality.

Symptoms Associated with Schizophrenia

The diagnosis of schizophrenia or any other mental disorder can only be made by a licensed mental health physician. Schizophrenia is the major form of the psychotic disorders, which are disorders that result in a loss of reality in individuals. The key features associated with psychotic disorders are:

  • Delusions: Delusions are fixed beliefs that are not true and easily not altered in an individual in spite of evidence to the fact that they are not true. Delusions typically have a number of potential different themes, such as themes of persecution (being harassed, harmed, etc.), grandiosity (believing that one has some exceptional ability, is the long-lost son of a famous figure, etc.), erotomanic (the belief that someone is infatuated with them), somatic (focused on one’s health), or referential (the belief that certain aspects of the environment or actions of others are focused on the person specifically). Delusions in schizophrenia are typically quite bizarre, such as feeling that someone is inserting thoughts into one’s mind or someone is controlling them from the outside.
  • Hallucinations: Hallucinations are the experience of certain types of perceptions that occur without being accompanied by the actual sensory experience. The most common hallucination occurring in schizophrenia is the auditory hallucination, and this is most commonly experienced by hearing voices even though there are no voices actually there. Hallucinations can occur in any sensory modality, but most often are auditory or visual (seeing things that are not really there). Hallucinations differ from illusions in that hallucinations are sensory perceptions that actually do not really exist, whereas illusions are alterations of real existing sensory experiences, such as seeing colors brighter than they are, interpreting random or meaningless sounds as having specific meanings, etc.
  • Disorganized thoughts: Disorganized thinking is typically assessed through speech patterns and can occur in a number of different contexts, such as switching from one topic to another without any formal organization in speech (termed derailment or loose associations), being totally incoherent (often referred to as word salad), or straying off to completely unrelated issues (tangentiality).
  • Disorganized motor actions: The disorganized motor actions that can occur in with psychotic behaviors typically present as a lack of goal-directed behavior or catatonic behavior, which is a significant decrease in one’s reactivity to environmental stimuli. This can present as the person maintaining very rigid and odd body poses for hours at a time to a complete lack of verbal responses (mutism).
  • Negative symptoms: Negative symptoms are considered to be the most serious manifestations of psychosis. The most prominent negative symptoms in schizophrenia are diminished emotional expression, which is an obvious lack of emotional engagement and avolition, which presents as a decrease in self-initiated, motivated, personal activity. Other negative symptoms that may occur are alogia, which is diminished speech output; anhedonia, the inability to experience pleasure; and asociality, a significant decrease in engaging in social interactions. Individuals diagnosed with schizophrenia who present with prominent negative symptoms have poorer responses to treatment and poorer long-term outcomes than individuals diagnosed with other symptoms.

How Schizophrenia Is Diagnosed

In previous editions of the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders (DSM), schizophrenia was diagnosed according to one of five subtypes. Each subtype represented the major symptom associated with the manifestation of the disorder in the person, such as paranoid schizophrenia mainly manifesting paranoid hallucinations and/or delusions, catatonic schizophrenia basically manifesting as catatonic behavior, etc. In the most recent version of the DSM, the DSM-5, these subtypes have been eliminated due to research evidence suggesting that schizophrenia is one disorder that can express a number of different symptoms.  Schizophrenia is diagnosed according to the following criteria:

  • The individual must express two or more of the main symptoms of delusions, hallucinations, disorganized speech, disorganized behavior, or negative symptoms during a one-month time period and at least one of those symptoms must be either delusions, hallucinations, or disorganized speech. If the individual has been treated (e.g., with medication), they may not display the symptoms over an entire month, and the diagnostic criteria must take this into account.
  • The individual’s symptoms must result in significant dysfunction in one’s work, interpersonal relations, or self-care.
  • The individual must have displayed continuous signs of the disturbance for at least a six-month period and two of the symptoms must have been present during at least one month.
  • The symptoms cannot be due to another mental health disorder and cannot be attributable to the effects of medications, drugs, or other medical conditions.

The formal diagnostic criteria specifically lay out a number of other associated conditions indicating whether or not the individual is experiencing a first episode, whether or not the current presentation is acute or chronic, and whether or not there have been multiple episodes. In addition, a number of neurological conditions (e.g., encephalitis), medical conditions (e.g., hepatic encephalopathy), other psychotic disorders, and other mental health disorders (e.g., bipolar disorder) may resemble schizophrenia, and only trained clinicians are qualified to make these distinctions and produce a formal diagnosis.

What Is the Cause of Schizophrenia?

Schizophrenia is relatively uncommon and occurs over all cultures at a rate of about 1:100 individuals. In general, males and females have equal prevalence rates, although there is some indication that having predominantly negative symptoms may be more common in males. Early conceptualizations of schizophrenia pointed to poor child-rearing and stressful childhood experiences as the causes of the disorder; however, these theories are largely denounced. The general trend is to consider schizophrenia to be a biologically based condition that is a result of:

  • A disruption in the level of certain neurotransmitters in the brain: Initially, it was thought that schizophrenia was a result of depletions of the neurotransmitter dopamine; however, research has indicated that other neurotransmitters are most likely involved as well.
  • Strong genetic components: A good deal of research supporting genetic associations is based on the early findings that one monozygotic (identical) twin has an extremely high probability of being diagnosed with schizophrenia if their twin has the disorder. This strong relationship holds true in cases where the twins have been adopted separately to different families at birth. Monozygotic twins share 100 percent of their genetic material, and this is considered to be strong evidence that there is a solid genetic component to schizophrenia; however, the relationship is far from perfect. Typically, a little over 50 percent of those who have a twin diagnosed with schizophrenia will also develop the disorder or a similar disorder. Thus, genetic explanations cannot account entirely for the expression of schizophrenia.
  • A combination of genetic and environmental factors: A number of other models exist that note that psychotic disorders like schizophrenia must result from some combination of genetic factors and the interaction of experience (environmental factors). It is believed that this combination somehow contributes to the development of the disorder (sometimes termed the diathesis stress model). These environmental factors can range from early infections in the mother, such as influenza during pregnancy, to a number of other issues.

At the current time, the cause of schizophrenia is unknown. There are probably a number of different interacting causes that result in various different presentations of schizophrenia.


The first line treatment for schizophrenia consists of medications. The first group of medications used in the treatment of schizophrenia was actually discovered to be of use by accident. These medications include major tranquilizers like Thorazine, which also inevitably result in a number of neurological conditions, such as tardive dyskinesia (involuntary movements of the face in other parts of the body), with long-term use.

Other drugs with greater efficacy and fewer side effects have been developed, and these drugs are typically classified as antipsychotic drugs. They include a number of familiar names, such as Risperdal (risperidone), Zyprexa (olanzapine), Seroquel (quetiapine), Abilify (aripiprazole), etc.  Newer classes of antipsychotic drugs target combinations of neurotransmitters, such as dopamine and serotonin, and have fewer serious side effects.

Psychotherapy can be used to assist in the treatment of schizophrenia, especially with adjustment issues, teaching living skills, and other forms of psychoeducation; however, it is not generally considered to be the first-line treatment approach for schizophrenia.

Substance Abuse and Schizophrenia

Other common co-occurring substance use issues in individuals diagnosed with schizophrenia include:

  • Cannabis use disorders
  • Alcohol use disorders
  • Prescription drug abuse
  • Use of street drugs, such as heroin, cocaine, etc.

For many individuals, the image of a person diagnosed with schizophrenia is one of a psychotic killer. Schizophrenia is often vilified in the media, especially in movies where psychotic killers often have schizophrenia-like symptoms. While a very small proportion of individuals with schizophrenia do commit serious crimes including murder, the vast majority of individuals with schizophrenia are not dangerous. Vagrancy as a result of being homeless is the most common crime associated with individuals who are diagnosed with schizophrenia.

Individuals with schizophrenia are at risk to also have co-occurring substance abuse issues. According to APA and other sources, the most common substance use disorder associated with schizophrenia is tobacco use disorder. Individuals with schizophrenia are notorious for being chain smokers. There is research suggesting that nicotine may have a beneficial effect on a number of the symptoms of schizophrenia, and this may be why tobacco abuse is so common in this particular group. Nonetheless, chronic and frequent use of tobacco is associated with a number of serious health effects and the potential to develop serious diseases, such as cancer, heart disease, other cardiovascular disease, etc. As a result, the risks of chronic cigarette smoking far outweigh any advantages it may produce in this group.

The approach to treating an individual with schizophrenia who also has a co-occurring substance use disorder includes the use of antipsychotic medications and a formal substance use disorder treatment program. Individuals with predominantly negative symptoms may require very intensive and targeted interventions. There is evidence that successful treatment of schizophrenia using antipsychotic medications may also result in a decrease in the use of drugs in these individuals; however, the general approach to treating individuals who have co-occurring diagnoses is the use of an integrated treatment program that relies on a multidisciplinary team consisting of physicians (in this case, most likely a psychiatrist and addiction medicine physicians), psychologists, counselors and social workers, and other therapists from different disciplines, including speech therapists, occupational therapists, case managers, etc. The treatment team works together to address treatment issues and to tailor the program to suit the person’s needs and abilities.

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