Folie à deux

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Induced delusional disorder
Classification and external resources
Specialtypsychiatry, psychotherapy

Folie à deux (UK: /ˌfɒli æ ˈdɜː, -i ɑː-/, US: /fˌl ə ˈdʌ/;[1] French: [fɔli a dø]; French for "madness of two"), or shared psychosis,[2] is a psychiatric syndrome in which symptoms of a delusional belief and sometimes hallucinations[3][4] are transmitted from one individual to another.[5] The same syndrome shared by more than two people may be called folie à trois, folie à quatre, folie en famille ("family madness"), or even folie à plusieurs ("madness of several").

Recent psychiatric classifications refer to the syndrome as shared psychotic disorder (DSM-IV – 297.3) and induced delusional disorder (F24) in the ICD-10, although the research literature largely uses the original name. This disorder is not in the current DSM (DSM-5). The disorder was first conceptualized in 19th-century French psychiatry by Charles Lasègue and Jean-Pierre Falret and is also known as Lasègue-Falret syndrome.[3][6]


This syndrome is most commonly diagnosed when the two or more individuals concerned live in proximity and may be socially or physically isolated and have little interaction with other people. Various sub-classifications of folie à deux have been proposed to describe how the delusional belief comes to be held by more than one person :

  • Folie imposée is where a dominant person (known as the 'primary', 'inducer' or 'principal') initially forms a delusional belief during a psychotic episode and imposes it on another person or persons (known as the 'secondary', 'acceptor' or 'associate') with the assumption that the secondary person might not have become deluded if left to his or her own devices. If the parties are admitted to hospital separately, then the delusions in the person with the induced beliefs usually resolve without the need of medication.
  • Folie simultanée describes either the situation where two people considered to suffer independently from psychosis influence the content of each other's delusions so they become identical or strikingly similar, or one in which two people "morbidly predisposed" to delusional psychosis mutually trigger symptoms in each other.[7]

Folie à deux and its more populous cousins are in many ways a psychiatric curiosity. The current Diagnostic and Statistical Manual of Mental Disorders states that a person cannot be diagnosed as being delusional if the belief in question is one "ordinarily accepted by other members of the person's culture or subculture" (see entry for delusion). It is not clear at what point a belief considered to be delusional escapes from the folie à... diagnostic category and becomes legitimate because of the number of people holding it. When a large number of people may come to believe obviously false and potentially distressing things based purely on hearsay, these beliefs are not considered to be clinical delusions by the psychiatric profession and are labelled instead as mass hysteria.

Related phenomena[edit]

Reports have stated that a phenomenon similar to folie à deux was induced by the military incapacitating agent BZ in the late 1960s.[8][9]

Individual cases[edit]

In May 2008, in the case of twin sisters Ursula and Sabina Eriksson,[10] Ursula ran into the path of an oncoming articulated lorry, sustaining severe injuries. Sabina then immediately duplicated her twin's actions by stepping into the path of an oncoming car; both sisters survived the incident with severe but non-life-threatening injuries. It was later claimed that Sabina Eriksson was a 'secondary' sufferer of folie à deux, influenced by the presence or perceived presence of her twin sister, Ursula – the 'primary'. Sabina later told an officer at the police station, "We say in Sweden that an accident rarely comes alone. Usually at least one more follows – maybe two."[11] However, upon her release from hospital, Sabina behaved erratically before stabbing a man to death.[12][13][14]

Another case involved Margaret and her husband Michael, both aged 34 years, who were discovered to be suffering from folie à deux when they were both found to be sharing similar persecutory delusions. They believed that certain persons were entering their house, spreading dust and fluff and "wearing down their shoes". Both had, in addition, other symptoms supporting a diagnosis of emotional contagion, which could be made independently in either case.[15]

The 2011 independent film Apart depicts two lovers affected and diagnosed with induced delusional disorder, trying to uncover a mysterious and tragic past they share. In a 2011 interview, director Aaron Rottinghaus stated the film was based on research from actual case studies.[16][17]

In 2016, a case involving a family of five from Melbourne, Australia made headlines when they abruptly fled their home and travelled more than 1,600 km (1,000 mi) across the state of Victoria because some of the family had become convinced someone was out to kill and rob them. No such evidence was found by the police, and the symptoms of those involved resolved on their own once the family returned to their home.[18]

In November, 2017, in the show Chance (Season 2, Episode 9 "A Madness of Two"), it was revealed the villains are suffering from this condition.

The book Bad Blood: Secrets and Lies in a Silicon Valley Startup suggests that this ailment plagued the founder of Theranos, Elizabeth Holmes, and her boyfriend/business partner Ramesh Balwani.

It was suspected a family of eleven members from Burari, India suffered from this condition[19][20]. On June 30, 2018, the family committed suicide due to the shared belief of one of its members.[21]

See also[edit]


  1. ^ Wells, John C. (2008), Longman Pronunciation Dictionary (3rd ed.), Longman, p. 665, ISBN 9781405881180
  2. ^ Berrios G E & Marková IS (2015) Shared Pathologies. In Bhugra D & Malhi G (eds) Troublesome disguises. Managing challenging Disorders in Psychiatry. 2nd Edition, London, Wiley, pp3-15
  3. ^ a b Arnone D, Patel A, Tan GM (2006). "The nosological significance of Folie à Deux: a review of the literature". Annals of General Psychiatry. 5: 11. doi:10.1186/1744-859X-5-11. PMC 1559622. PMID 16895601.
  4. ^ Dantendorfer K, Maierhofer D, Musalek M (1997). "Induced hallucinatory psychosis (folie à deux hallucinatoire): pathogenesis and nosological position". Psychopathology. 30 (6): 309–15. doi:10.1159/000285071. PMID 9444699.
  5. ^ "Dr. Nigel Eastman in the BBC documentary 'Madness In The Fast Lane'". 2010-09-24. Archived from the original on 2010-10-01. Retrieved 2011-05-31.
  6. ^ Berrios G E (1998) Folie à deux (by W W Ireland). Classic Text Nº 35. History of Psychiatry 9: 383–395
  7. ^ Dewhurst, Kenneth; Todd, John (1956). "The psychosis of association: Folie à deux". Journal of Nervous and Mental Disease. 124: 451–459. doi:10.1097/00005053-195611000-00003.
  8. ^ "Incapacitating Agents". Retrieved 2011-05-31.
  9. ^ "Medscape Access". Retrieved 2011-05-31.
  10. ^ "TV Review: Madness In The Fast Lane – BBC1". The Sentinel. 11 August 2010. Retrieved 31 August 2010.
  11. ^ "TV Preview: Madness In The Fast Lane – BBC1, 10.35 pm". The Sentinel. 10 August 2010. Retrieved 31 August 2010.
  12. ^ "Why was Sabina Eriksson free to kill?". The Sentinel. 3 September 2009. Retrieved 31 August 2010.
  13. ^ "Could M6 film of killer have saved victim?". The Sentinel. 7 September 2009. Retrieved 31 August 2010. |first1= missing |last1= in Authors list (help)
  14. ^ Madness In The Fast Lane Archived 2010-10-01 at the Wayback Machine. Retrieved 3 February 2011.
  15. ^ This case study is taken from Enoch and Ball's 'Uncommon Psychiatric Syndromes' (2001, p181)
  16. ^ Cangialosi, Jason. "SXSW 2011: Interview with Aaron Rottinghaus, Director of 'Apart'". Yahoo!. Archived from the original on 29 April 2014. Retrieved 13 August 2013.
  17. ^
  18. ^ "Tromp family: The mystery of a tech-free road trip gone wrong - BBC News". Retrieved 2016-09-07.
  19. ^
  20. ^
  21. ^

Further reading[edit]