A delusion is a belief based on an inaccurate interpretation of reality, despite clear evidence to the contrary. A delusional disorder causes a person to have delusional thoughts for a prolonged period.

Delusional disorder is a mental illness. A person with delusional disorder has one or more delusional thoughts for 1 month or longer. Delusional thoughts do not have to be totally unbelievable or outside the realms of possibility, but they are often not based on reality.

Keep reading to learn more about delusional disorder, including the symptoms, causes, and treatment or management of the condition.

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Delusional disorder is a mental illness that causes a person to have delusional thoughts for a prolonged period.

A person with delusional disorder will have delusional thoughts that are not entirely bizarre or unrealistic. They are usually based on something that could possibly happen to the person in real life, such as someone following or deceiving them.

A person with delusional disorder will not usually exhibit overtly bizarre behavior, and their delusions often do not affect their ability to function.

Delusional disorder is a rare condition, with estimates suggesting that the probability of a person developing it during their lifetime is as low as 0.05–0.1%. The condition is equally prevalent across genders. It also has a later general onset than schizophrenia, with which it shares some characteristics.

A person with delusional disorder will have illusory thoughts that contradict readily available evidence.

Their delusions are usually not overtly bizarre and could be possible. However, there is often plenty of evidence to suggest that these thoughts are not based on reality.

A person’s delusions often center on an inaccurate interpretation of an external reality.

Some of the more common types of delusions are:

  • Delusional jealousy: A person may incorrectly think that their partner is being unfaithful.
  • Romantic: The individual may believe that another person is in love with them.
  • Grandiose: A person may have inflated self-worth and power and believe that they have great talent or knowledge.
  • Persecutory: This occurs when the person believes that others are attacking or conspiring against them or being obstructive to prevent them from attaining long-term goals.
  • Somatic: The individual may believe that their appearance or bodily functions are grossly abnormal.
  • Thought broadcasting: This type refers to the idea that others are perceiving the person’s thoughts.
  • Thought insertion: A person may think that an external source or entity is inserting their thoughts into their mind.
  • Bizarre: A person may believe in a phenomenon that is impossible and unrelated to normal life.

According to researchers, persecutory and jealous delusions are more common in males, whereas romantic delusions are more common in females.

Other than the presence of delusions, a person with delusional disorder does not have impaired functionality, and their behavior is not obviously bizarre.

People with delusional disorder tend not to have hallucinations or other psychotic or marked mood symptoms.

The exact causes of delusional disorder are not well-understood. However, research suggests that various biological factors, including substance use, medical conditions, and neurological conditions, can cause delusions.

It also indicates that hypersensitivity and ego defense mechanisms, such as reaction formation, projection, and denial, may be linked with delusional disorder.

Other studies have suggested that exposure to trauma could be linked to the development of psychotic episodes.

Treating delusional disorder is generally challenging. Doctors frequently use antipsychotic medications to treat the disorder, as well as psychological therapies such as cognitive behavioral therapy (CBT).

However, there is some doubt over the effectiveness of these treatments. The authors of a 2015 study state that there is insufficient research to make evidence-based recommendations for treatments for delusional disorder.

They also note that until further studies take place, it is reasonable to offer treatments that are effective in treating other psychotic disorders to people with delusional disorder.

Several mental illnesses share similarities with delusional disorder. However, they are all different in various ways. These similar conditions include:


The hallmark of schizophrenia is a disrupted thought process. This mental disorder also affects perceptions, social interactions, and emotional responsiveness. Schizophrenia can be severe and disabling.

The symptoms of schizophrenia include:

  • hallucinations, delusions, and thought disorders
  • unusual ways of thinking
  • reduced expression of emotions
  • reduced motivation to accomplish goals
  • difficulty in social relationships
  • motor impairment
  • cognitive impairment

Learn more about schizophrenia here.

Obsessive-compulsive disorder (OCD)

OCD is a long lasting, chronic disorder. A person with OCD often has recurring thoughts and obsessions, and they may also feel compelled to repeat certain behaviors.

Common obsessions include:

  • fear of germs and contamination
  • unwanted thoughts regarding taboo subjects, such as harm or sex
  • aggressive thoughts toward other people and themself
  • having items in perfect order or placing them symmetrically

Common compulsions and repetitive behaviors include:

  • excessive cleaning
  • excessive hand washing
  • placing items in a certain order or a precise, particular way
  • repeatedly checking things, such as whether the door is locked
  • compulsive counting

Although many people may experience some of the above from time to time, a person with OCD generally cannot control their thoughts or behaviors, even if they recognize them to be excessive.

Learn more about OCD here.


Depression is a very common mental illness and a leading cause of disability worldwide. Depression is more than occasionally feeling sad or unhappy. It is a serious mental health issue that requires both understanding and medical care.

Common symptoms of depression include:

  • changes in sleep and appetite
  • the inability to concentrate
  • loss of energy and lack of interest in activities
  • a feeling of hopelessness
  • guilty thoughts
  • physical aches and pains
  • suicidal thoughts

Delusional thoughts can sometimes occur with different mood episodes.

Learn more about depression here.

Bipolar disorder

A person with bipolar disorder can experience unusual changes in mood, energy, activity levels, and concentration. This condition can also affect a person’s ability to carry out tasks.

Common symptoms of bipolar disorder include:

  • periods of intense emotion — both manic and depressive
  • changes in sleep patterns
  • changes in activity levels
  • uncharacteristic behaviors, usually without recognizing their harmful or undesirable effects

Some people with bipolar disorder can experience both manic and depressive symptoms at the same time. A person with more severe bipolar disorder can also experience psychotic symptoms, which can include hallucinations or delusions.

Learn more about bipolar disorder here.

A person should seek medical help from a qualified professional as soon as possible if they or a loved one is experiencing delusions. Early intervention and mental health support can have a positive effect on the person’s outlook.

Delusional disorder is a mental illness that causes a person to have delusional thoughts. Generally, these delusions are not overly bizarre or unrealistic. However, they are based on an inaccurate interpretation of reality.

Most of the time, there is plenty of evidence available to suggest that the thoughts are not rooted in reality.

Common delusions that a person may experience include the belief that someone is conspiring against them, becoming infatuated with them, or being unfaithful to them.

Delusions can also occur due to other mental health issues, such as schizophrenia. A person should seek medical help right away if they or a loved one is experiencing delusions.

Doctors often use antipsychotic medication and psychological therapies to treat delusional disorder.