What Is Delusional Disorder?

Delusional disorder is a mental health condition where a person struggles to tell what is real from what is imagined. It is characterised by certain ideas or beliefs the person has which are not true or real, these are known as delusions. People experiencing these delusions often have little to no insight into these delusions and will continue to believe them, even when presented with evidence to the contrary. 


Delusional disorder is a mental health condition categorised in the International Classification of Diseases (ICD-11) under the subcategory of “schizophrenia and other primary psychotic disorders”. Delusions are fixed, false beliefs based on their false interpretations of reality despite evidence contradicting their validity. Delusional disorder is characterised by the presence of one or more of these delusional ideas or beliefs that are persistent for 3 months and cannot be better explained by another condition.

The delusions in delusional disorder are non-bizarre, meaning that they are not real, but also, it is not impossible that they could occur.1

It is important to note that when considering a diagnosis of a delusional disorder, the individual’s cultural and religious beliefs must be taken into account.

Whilst delusional disorder shares many symptoms with schizophrenia, it differs in that the delusions are present but no other symptoms of psychosis are present.2

The mean age of onset is 40 years old, but the age ranges from 18 to 90 years old.1

Types of delusional disorder

Delusions usually focus on a particular theme such as guilt, infidelity, love, persecution, or religion.

Types of delusions include:

  • Erotomanic: Erotomania is a type of delusion where the individual thinks that a person of importance or a famous person is interested in them intimately. This can result in persistent attempts to contact the person which may constitute stalking and harassment.2
  • Grandiose: People experiencing this type of delusion often overestimate their importance, value, influence, or expertise. They often make claims to being highly important, talented or to have done something of great significance.
  • Jealous: Jealous delusions typically involve the person being suspicious about their spouse or partner being unfaithful.
  • Persecutory: People with persecutory delusions will believe something is being done to them despite no objective evidence. These can be ideas that someone is trying to harm them, that they are being mistreated, or that they are being watched or monitored.2 A person with persecutory delusions may make several complaints or contact the police repeatedly as a result of what they believe to be true.
  • Somatic: This type of delusion has people thinking that they have a mental or physical health condition despite there being no evidence of such.
  • Mixed: This is when a person has two or more of the above types of delusions.

Persecutory and jealous delusions are found to be more common in people assigned male at birth, whilst erotomania is more common in people assigned female at birth.1

Causes of delusional disorder

There is no, one clear cause for delusional disorder that has been found, but it is thought that multiple factors can contribute to, or increase the risk of developing this condition.1 Certain personal traits such as being paranoid, mistrusting, or suspicious may be more susceptible to developing a delusional disorder.1

There are biological factors such as brain chemistry influencing the development of delusions. One study explores the current theory that dopamine dysfunction plays a large part in the development of psychosis, including delusions.3

It is thought, as with many other mental health conditions, that genetics factor into one’s susceptibility to developing a delusional disorder. Delusional disorders are said to be more common in those who have a family history of schizophrenia or delusional disorder.

Other factors such as alcohol or illicit drug use and high levels of stress may trigger a delusional disorder. Social isolation and low self-esteem may compound these also to increase the risk of developing a delusional disorder. 

Signs and symptoms of delusional disorder

The main sign that someone is experiencing a delusional disorder is that they will express ideas and beliefs that are not real, but they will believe them to be real. They can experience one or more of these types of delusion as reported above.

Unlike with schizophrenia, people with delusional disorder typically continue to function well. They do not usually display odd or bizarre behaviours. However, their behaviours and attitudes may change in congruence with their delusional disorder. It is normal that someone with a delusional disorder will not accept that their ideas and beliefs are not real.

A person’s behaviours and attitudes will vary depending on the nature of their delusions, for example, someone with erotomania may stalk or harass the individual at the focus of their attention. Someone with a jealous delusion may be mistrusting, hostile, or aggressive towards their spouse or partner. 

Management and treatment for delusional disorder

A study looking into dopamine function and delusional disorder found that people with this disorder responded well to Haloperidol (an antipsychotic), even at low doses.4 There are a number of other effective antipsychotic medications and the medication prescribed will vary. Your psychiatrist will prescribe whichever medication they feel is best following a comprehensive assessment.

A combined approach offers the best chances of both recovery and relapse prevention. Cognitive behavioural therapy (CBT) is an established psychological treatment option to augment medication.5 There are difficulties however with treatment when it comes to delusional disorder. The fact that the person will likely lack insight into their delusions, believing them real poses a significant challenge. People experiencing this disorder may not attend appointments with medical professionals, as they may not see that they have a problem that requires treatment. There is an additional challenge that cognitive behavioural therapy requires a trusting working relationship between the therapist and the person, which may not initially be there due to the delusions.

If an individual has been diagnosed with a delusional disorder, they will likely be supported by a mental health team who will review their progress regularly, including the efficacy of medications and psychological treatment.

Whilst treatment in the community setting is a preferred and often more successful option, there is the option of treatment in a mental health hospital if the person is not concordant with their treatment, or if they pose a risk to themselves or others as a result of their delusions. 


Diagnosis is made following a comprehensive mental health assessment, and once other reasons for the delusions have been ruled out. There are many other illnesses and conditions that can cause delusions, such as Parkinson’s disease, dementia, delirium (including from alcohol withdrawal), schizophrenia, bipolar affective disorder, obsessive-compulsive disorder (OCD), eating disorder, brain tumour or drug or alcohol intoxication. These will need to be ruled out before a diagnosis of delusional disorder can be made.

The delusions must be persistent for three months (stipulated by the ICD-11), or if the DSM-5 is being used, they only need to be persistent for one month or more. In the UK ICD-11 is used primarily. 


If delusional disorders are left untreated, they can lead to other mental health conditions such as depression and anxiety, which will compound the disorder. There is the risk of changes in behaviour in the context of delusional beliefs. For example, someone with erotomanic delusions may pursue contact with the person they are focused on, which often includes stalking or harassment, which will lead to police involvement, and possibly a criminal record. Or someone with a jealous delusion may become angry, irritable, or aggressive towards a spouse or partner. A person with somatic delusions may persistently seek medical help for a condition they are convinced they have, leading to feeling they are being dismissed by medics. There are many more complications that could arise as a result of delusional disorder not being noticed or treated. 


How can I prevent delusional disorder?

As the cause is unclear, it may not be possible to prevent delusional disorder. However, when looking at the risk factors, it may be possible to optimise your overall well-being and reduce the risk of you developing a delusional disorder. For example, avoiding illicit drug use or excessive alcohol use, and developing mental and emotional resilience, either self-taught or through psychological therapies. You can also learn to challenge automatic negative thoughts and beliefs through psychological therapies such as cognitive behavioural therapy (CBT). Part of developing resilience might be to reduce your social isolation by gaining employment, joining a group of people with similar interests, or seeing friends and family regularly. 

How common is delusional disorder?

Documented cases of delusional disorder are rare, much rarer than cases of schizophrenia and bipolar affective disorder, for example. It is said that the prevalence of delusional disorder in the general population is 0.2%.1 It is likely that is under-reported due to those holding the delusional beliefs not seeing that they are untrue, therefore seeing no reason to see a doctor or seek help. 

Who is at risk of delusional disorder?

Anyone could develop a delusional disorder. Those at higher risk, however, are reportedly those who have a relative with a history of schizophrenia or delusional disorder. Also, people at risk are those who are suspicious, mistrusting, have low self-esteem, self-isolate, take illicit drugs or consume excessive alcohol, or are experiencing high levels of stress.

Other population groups who are more susceptible to delusional disorder are the elderly, people who do not speak the native language, such as immigrants, and people with sensory impairments such as blindness and deafness.1

When should I see a doctor?

The short answer is “immediately”. If you are experiencing any form of psychosis, which includes delusions, you should see your doctor and get a specialist mental health assessment. The prognosis is good and treatment is usually effective with prompt intervention. However, due to the nature of the condition, you will unlikely see that you are experiencing delusions because you think your ideas and beliefs are real. It is more likely that a friend or family member will notice your delusions and ask you to see a doctor. 


Delusional disorder is a rare mental health disorder characterised by delusions that the individual believes are real despite there being evidence to the contrary. The delusional beliefs are very real to the person and can be very distressing. It is possible that the person may act on their delusions which may lead to relationship breakdowns, harm, or involvement with the police.

It is different from other psychotic presentations such as schizophrenia or bipolar affective disorder, in that there is no mood disorder present and no other symptoms of schizophrenia.

For diagnosis, all other possibilities must be ruled out first. There are a number of other illnesses and conditions that have delusions as part of the symptomology, however, when an underlying cause is found, that underlying cause is treated and the delusions dissipate and disappear.

Treatment with antipsychotic medication and psychological therapy is effective and the prognosis is good if the person is concordant with the treatment. 


  1. Joseph SM, Siddiqui W. Delusional disorder. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 [cited 2023 Jun 8].
  2. Manuel Z. Types and symptoms of delusional disorder. Journal of Psychology & Psychotherapy [Internet]. 2023 Feb 1 [cited 2023 Jun 8];13(1):1–1.
  3. Rootes-Murdy K, Goldsmith DR, Turner JA. Clinical and structural differences in delusions across diagnoses: a systematic review. Frontiers in Integrative Neuroscience [Internet]. 2022 [cited 2023 Jun 8];15.
  4. Morimoto K, Miyatake R, Nakamura M, Watanabe T, Hirao T, Suwaki H. Delusional disorder: molecular genetic evidence for dopamine psychosis. Neuropsychopharmacol [Internet]. 2002 Jun [cited 2023 Jun 8];26(6):794–801.
  5. Fear CF. Recent developments in the management of delusional disorders. Advances in Psychiatric Treatment [Internet]. 2013 May [cited 2023 Jun 8];19(3):212–20.
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

Get our health newsletter

Get daily health and wellness advice from our medical team.
Your privacy is important to us. Any information you provide to this website may be placed by us on our servers. If you do not agree do not provide the information.

Karl Jones

BA Hons in Learning Disability Nursing, Diploma in Mental Health Nursing (Oxford Brookes

Karl has 12 years of experience in learning disability and mental health nursing in a variety of
settings. He has worked predominantly in general hospitals specialising in suicide prevention and the
psychological impact on long term health conditions. Most recently he has worked as a clinical
educator in the field of mental health. He is currently focusing on writing as a career with the aim of
imparting his knowledge to a wider audience.

Leave a Reply

Your email address will not be published. Required fields are marked *

my.klarity.health presents all health information in line with our terms and conditions. It is essential to understand that the medical information available on our platform is not intended to substitute the relationship between a patient and their physician or doctor, as well as any medical guidance they offer. Always consult with a healthcare professional before making any decisions based on the information found on our website.
Klarity is a citizen-centric health data management platform that enables citizens to securely access, control and share their own health data. Klarity Health Library aims to provide clear and evidence-based health and wellness related informative articles. 
Klarity / Managed Self Ltd
Alum House
5 Alum Chine Road
Westbourne Bournemouth BH4 8DT
VAT Number: 362 5758 74
Company Number: 10696687

Phone Number:

 +44 20 3239 9818