What is the meaning and origin of the term Folie à deux?

The term Folie à deux is a French phrase that translates to madness of two or shared psychosis in English. It refers to a rare psychiatric disorder in which two individuals, often in a close relationship, share the same delusional beliefs. This condition has fascinated and perplexed medical professionals for centuries, leading to numerous studies and theories about its origins and treatment. In this essay, we will delve into the history and meaning of Folie à deux, exploring its cultural and psychological significance.

Folie à deux (or shared psychosis) is a psychiatric syndrome in which symptoms of a delusional belief are transmitted from one individual to another. The same syndrome shared by more than two people may be called folie à trois, folie à quatre, folie en famille or even folie à plusieurs (“madness of many”). Recent psychiatric classifications refer to the syndrome as shared psychotic disorder (DSM-IV) (297.3) and induced delusional disorder (F.24) in the ICD-10, although the research literature largely uses the original name. The disorder was first conceptualized in 19th century French psychiatry.



This case study is taken from Enoch and Ball’s ‘Uncommon Psychiatric Syndromes’ (2001, p181): Margaret and her husband Michael, both aged 34 years, 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.

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.

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.

In a well-publicised case in the United Kingdom, the condition was one of two possible diagnoses of a Swedish woman, Sabina Eriksson, who stabbed a man to death after he took her into his home, offering food and shelter. Eriksson had just been released from police custody following an incident on a motorway which grabbed news headlines. Caught on camera by a police documentary filmmaker, her twin sister ran into the path of an oncoming articulated lorry, sustaining severe injuries. Eriksson then immediately duplicated her twin’s actions by stepping into the path of an oncoming car; she survived the impact. The defence counsel in the ultimate murder trial claimed that Eriksson was a ‘secondary’ sufferer of folie à deux, influenced by the presence or perceived presence of her twin sister — the ‘primary’.


Related phenomena

Reports have stated that a similar phenomenon to folie à deux had been induced by the military incapacitating agent BZ in the late 60s, and most recently again by anthropologists in the South American rainforest consuming the hallucinogen ayahuasca (Metzner, 1999).

Similar experiences of folie à deux or even folie à plusieurs have been reported during Shamanic journeying in a group setting. A typical example is that of the interaction between power animals of two or more people who were guided in a Power-Animal retrieval journey during the same session and by the same Shaman.


Cultural References

The 19th episode of season 5 of the X-Files TV series and the fifth studio album of the American rock band Fall Out Boy are named after the syndrome.

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