Folie à deux

This is about the mental disorder, the studio album is at Folie à Deux (album)

Folie à deux is the name for a condition where an otherwise sane person develops the symptoms and delusions of a person suffering from psychosis. If more than two people share the symptoms or delusions, people speak about folie à trois (3), folie à quatre (4), folie à plusieurs, or folie en famille. Officially, the condition is known as induced delusional disorder or shared psychotic disorder today, but many publications still use the original terms, which were developed in France in the 19th century. Today, there are two main forms of the condition:

• Folie imposée: A person forms a delusion, and passes it on to other people. If the people get separated, the delusions in those people who did not develop them first will usually disappear quickly.
• Folie simultanée: Two people suffering from delusions influence each other so that their delusions become very similar.

Newer studies seem to indicate that this classification may not be sufficient to fully describe 'folie à deux'. There may be more symptoms than are usually described in the cases above. Also, in many cases, separating the two patients may not be enough to make the condition go away in one of them. Also, the person described as "sane" before developing the folie à deux may already be suffering from a psychiatric illness, or may develop one.

The condition was first described in an article pubilshed by Ernest-Charles Lasègue and Jules Farlet in 1877.

Mass hysteria can be seen as a form of folie à deux.