Home Clinical Psychology & Psychotherapy Delusional Disorder: Causes, Symptoms, Types & Treatment

Delusional Disorder: Causes, Symptoms, Types & Treatment

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Have you ever heard someone talking about things that don’t make any sense or have no basis in reality? If so, they may be suffering from delusional disorder. This is a mental illness that affects a person’s ability to think clearly and logically, leading them to believe things that are not true or have no evidence to support them.

What is delusional disorder?

Delusional disorder is a type of mental illness that is characterised by the presence of delusions, which are false beliefs that are held despite clear evidence to the contrary. These delusions can be related to any aspect of a person’s life, including their health, relationships, work, or social life. Delusional disorder is considered a rare condition, affecting less than 0.2% of the population.

Causes of delusional disorder

The exact cause of delusional disorder is not known, but it is believed to be a combination of genetic, environmental, and neurological factors. Some possible causes of delusional disorder include:

  • Genetics. Some studies suggest that certain genes may make a person more susceptible to developing a delusional disorder.
  • Brain chemistry. Changes in the levels of neurotransmitters in the brain, such as dopamine and serotonin, may play a role in the development of delusional disorder.
  • Environmental factors. Trauma, abuse, and stressful life events may trigger the onset of delusional disorder.

Symptoms of delusional disorder

The main symptom of delusional disorder is the presence of delusions. These delusions can take many forms, including:

  • Paranoid delusions. Believing that others are out to harm or persecute them
  • Grandiose delusions. Believing that they have special abilities, talents, or qualities that make them superior to others
  • Somatic delusions. Believing that they have a physical illness or disease that does not actually exist
  • Erotomanic delusions. Believing that someone is in love with them, even when there is no evidence to support this belief

In addition to these delusions, people with delusional disorder may also experience other symptoms, such as:

  • Anxiety
  • Depression
  • Social isolation
  • Anger or irritability
  • Hallucinations (in some cases)

Delusional Disorder vs schizophrenia

Delusional disorder is often confused with schizophrenia, as both conditions involve delusions. However, there are some key differences between the two.

One of the main differences is that delusional disorder does not typically involve hallucinations or disordered thinking, which are common in schizophrenia. People with delusional disorders may have normal thought processes and perceptions aside from their delusions.

Additionally, delusional disorder tends to be less severe and less impairing than schizophrenia. People with delusional disorder are often able to function normally in other areas of their lives, such as work or relationships, while those with schizophrenia may struggle with day-to-day tasks.

Delusional parasitosis

Delusional parasitosis is a type of delusional disorder in which a person believes that they are infested with parasites, despite medical evidence to the contrary. This can lead to intense distress and can cause the person to engage in behaviours such as excessive cleaning or self-harm.

Types of delusional disorder

There are several other types of delusional disorder, including:

  • Persecutory type. Delusions involve the belief that they are being spied on, followed, or targeted in some way.
  • Erotomanic type. Delusions involve the belief that someone is in love with them, often someone of higher status such as a celebrity or politician.
  • Grandiose type. Delusions involve exaggerated beliefs about one’s own abilities, knowledge, or importance.
  • Jealous type. Delusions involve the belief that a partner or spouse is being unfaithful.
  • Somatic type. Delusions involve bodily functions or sensations, such as the belief that one is infested with parasites.

What does a psychotic episode look like?

A psychotic episode is a period of time during which an individual experiences symptoms of psychosis. These symptoms may include delusions, hallucinations, disordered thinking, and abnormal behaviour. The experience of a psychotic episode can be very distressing and may cause significant impairment in daily functioning.

During a psychotic episode, an individual may experience delusions, which are false beliefs that are not based on reality. These beliefs may be bizarre or implausible, and the individual may be convinced that they are true despite evidence to the contrary. For example, a person with a delusional disorder persecutory type may believe that they are being followed, watched, or harmed by others, despite no evidence to support these beliefs.

Hallucinations may also occur during a psychotic episode. These are sensory experiences that are not based on reality. The most common type of hallucination is auditory, where the person may hear voices or other sounds that are not present. They may also experience visual, olfactory, or tactile hallucinations.

Disordered thinking may be present during a psychotic episode, and the person may have difficulty expressing themselves or maintaining a coherent conversation. They may jump from topic to topic or provide responses that are unrelated to the question asked.

Abnormal behaviour may also occur during a psychotic episode. The person may behave in a way that is unusual or inappropriate, such as laughing at inappropriate times, speaking loudly or rapidly, or engaging in self-injurious behaviour.

It is important to note that not all individuals with psychotic disorders experience all of these symptoms, and the severity and duration of symptoms can vary greatly from person to person.


Delusional disorder is a mental illness characterized by persistent, false beliefs that are not based on reality. It can be a very distressing condition for those who experience it and can cause significant impairment in daily functioning. However, with proper diagnosis and treatment, individuals with delusional disorders can learn to manage their symptoms and improve their quality of life.

It is important to seek help from a qualified mental health professional if you or someone you know is experiencing symptoms of a delusional disorder. Treatment may include medication, therapy, and support from family and friends.

Understanding the symptoms and causes of delusional disorder is crucial for promoting awareness and reducing the stigma surrounding mental illness. By raising awareness and providing support for those who are affected, we can help individuals with delusional disorders live fulfilling and productive lives.


What triggers delusional disorder?

The exact triggers of delusional disorder are not known. However, like many mental disorders, it is believed to be caused by a combination of genetic, biological, and environmental factors.

Some possible triggers include:

  • Trauma or stress
  • Substance abuse
  • Chronic illness or disability
  • Social isolation or loneliness
  • Family history of mental illness

Does a delusional person know they are delusional?

In many cases, people with delusional disorders are unaware that their beliefs are not based on reality. This is because their delusions are so strongly held that they feel real and true to them.

However, some people with delusional disorders may be able to recognise that their beliefs are unusual or out of the ordinary. This can lead to feelings of shame or embarrassment and may cause the person to hide their delusions from others.

What not to say to a delusional person?

If you know someone who is struggling with a delusional disorder, it’s important to be supportive and understanding. Here are some things to avoid saying:

“That’s crazy.” This dismisses the person’s experiences and can make them feel ashamed or embarrassed.

“You’re being paranoid.” This can feel dismissive and invalidating to someone who is experiencing delusions.

“You need to snap out of it.” This implies that the person has control over their delusions, which is not necessarily the case.

Instead, try to listen actively and offer support and understanding. Encourage the person to seek professional help if necessary.

Mavra Farrukh, MD has a particular interest in the fields of public health, rheumatology, preventive medicine and research. 

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