Delusions — beliefs that are inflexible even when proven untrue — are a core feature of both delusional disorder and schizophrenia, but these conditions aren’t the same. Here are the key differences.

Delusional disorder (DD) and schizophrenia are both psychotic disorders included in the Diagnostic and Statistical Manual of Mental Disorders, 5th edition, text revision (DSM-5-TR), an internationally used, evidence-based guide for diagnosing mental health conditions.

As psychotic disorders, they involve symptoms related to changes in the perception of reality that fall into the category of psychosis. Psychosis happens when your brain incorrectly processes information, creating a false reality. It can include experiences such as hallucinations, disorganized thinking, negative symptoms, disorganized motor function, and delusions.

Delusions are beliefs, thoughts, and ideas you rigidly adhere to despite unquestionable proof that they’re false. You believe in delusions and can’t be convinced otherwise.

Both DD and schizophrenia include delusions as a core diagnostic symptom, but other differences set these disorders apart.

DD is a psychotic disorder. According to the DSM-5-TR, it can be diagnosed after you’ve experienced at least one delusion for 1 month or longer. While delusions can take on any theme, common types seen in DD include:

  • Erotomanic: believing someone is in love with you when they aren’t
  • Grandiose: believing you are superior to others in some often-unrecognized way
  • Jealous: believing that your significant other is unfaithful when they are, in fact, loyal
  • Persecutory: believing that people are conspiring against you or continuously, actively opposing you in some way
  • Somatic: believing delusions about bodily functions or sensations

It’s not necessary to have one prominent type of delusion to receive a DD diagnosis. The terms “mixed type” and “unspecified type” are used to describe unique or multiple delusion themes.

Symptoms of delusional disorder

Delusions are the primary symptom of DD, but mood episodes, hallucinations, and behavioral changes are also possible. The DSM-5-TR clarifies these experiences in DD as follows:

  • Hallucinations, if present, are aligned with the delusional theme (for example, if the delusion is about contamination, the hallucination would be about contamination).
  • Overall function is not significantly impaired, and behavior is not notably unusual.
  • If mood episodes occur, they’re brief and relative to the duration of a delusional period.
  • Delusions are not typically considered bizarre (implausible or not derived from ordinary experiences), but bizarre delusions are possible.

DD may also involve a lack of insight (anosognosia), which means you’re not consciously aware that your patterns of thinking are out of the ordinary.

Schizophrenia is a psychotic disorder involving multiple experiences of altered perception of reality. To receive a diagnosis according to the DSM-5-TR, you must be experiencing at least two symptoms of psychosis, and one of those symptoms must be hallucinations, delusions, or disorganized thinking.

While delusions are common in schizophrenia, they aren’t necessary for a schizophrenia diagnosis if two other core symptoms are present.

Symptoms of schizophrenia

Schizophrenia can feature a variety of cognitive, behavioral, and emotional disturbances that vary in severity. Symptoms necessary for diagnosis can be broken down into two categories:

  • Positive: Symptoms that add to baseline function, such as:
    • hallucinations
    • delusions
    • disorganized thinking
    • disorganized motor function
  • Negative: Symptoms that take away from baseline function, such as:
    • diminished ability to experience pleasure (anhedonia)
    • a decrease in self-motivated, purposeful action (avolition)
    • diminished emotional expression (flat affect)
    • reduced speech output (alogia)
    • lack of interest in interpersonal interaction (asociality)

Other symptoms that aren’t required for diagnosis but are sometimes associated with schizophrenia include:

  • mood episodes
  • inappropriate anger
  • depersonalization
  • derealization
  • cognitive impairment (challenges with memory, concentration, language, and other executive functions)
  • anosognosia
  • neurological symptoms

DD differs from schizophrenia in scope, severity, and duration of symptoms; age of onset; and diagnostic stability.

Symptom scope

DD is considered a disorder of delusions only. It can include hallucinations, but if they occur, they are directly related to the current false beliefs. Hallucinations are not necessary for a diagnosis of DD, and other features of psychosis are absent.

Schizophrenia, on the other hand, often involves a variety of positive, negative, and cognitive symptoms. It can include all symptoms under the umbrella of psychosis. Hallucinations and delusions are prominent features.

You can receive a diagnosis of schizophrenia without delusions when other psychosis symptoms are present.

Severity and duration

The DSM-5-TR indicates that DD is less severe overall than schizophrenia. While delusions can cause impairment in areas related to their theme, other areas of functioning typically remain stable. For example, jealous type DD may negatively affect your relationship but not your job, social life, or educational pursuits.

In DD, symptoms must last only 1 month for a diagnosis.

Schizophrenia is associated with significant impairment across multiple areas of functioning, and symptoms must be present for 6 months or longer to receive a diagnosis.

Diagnostic stability

Schizophrenia is a lifelong condition that can be progressive, especially if left untreated.

DD can also be a lifetime condition, but an initial diagnosis of DD may change if other symptoms emerge. For example, according to a 4-year follow-up study in Chinese adults, 35% of people who received a DD diagnosis after their first psychotic episode shifted to a diagnosis of schizophrenia by the 4-year mark.

Older research from 2014 suggests that this shift occurs in about 20% of people who receive a diagnosis of DD.

Age of onset

Another defining difference between schizophrenia and DD is the age of onset. According to a 2022 review, the age of onset in schizophrenia is the late teens to early adulthood, while in DD it is middle age and older.

Psychotic disorders can occur at the same time, or be “comorbid” with one another. Theoretically, this means it may be possible to have both DD and schizophrenia.

In most cases, the appearance of other psychotic symptoms and greater impairment would shift a diagnosis of DD to schizophrenia or another mental health condition, but these conditions aren’t always that linear or clearly defined.

It may be possible for evolving symptoms to warrant a dual diagnosis, but there is no current data to show how common this specific pairing is.

DD and schizophrenia are treated similarly. Antipsychotic medications are the first-line treatment to help reduce symptoms of psychosis that may cause major impairment, reduce the effectiveness of psychotherapy, or pose safety risks.

Antipsychotics are paired with psychotherapy approaches that center on forming trust and safety. Laying these foundations helps encourage open communication, which can otherwise be difficult when you’re experiencing altered perceptions of reality.

Cognitive behavioral therapy for psychosis (CBTp) is a specific type of therapy used for psychotic disorders, but different therapy formats may be involved in DD and schizophrenia treatment depending on your individual needs.

Medications such as antidepressants, anti-anxiety medications, or sleep aids may also be prescribed for common symptoms of psychotic disorders.

Delusional disorder and schizophrenia are both psychotic disorders that can feature delusions, but they are separate diagnoses.

Symptom scope, severity, and duration; diagnostic stability; and age of onset are clinical features that set DD and schizophrenia apart.