Induced delusional disorder is also known as induced psychosis. It is a disease characterized by systematic delusions. It often occurs in relatives or close friends who live in the same environment or family for a long time and have close contact, such as mother and daughter, sisters, or husband and wife, and teachers and students. Generally, there are two patients with very similar mental symptoms, one of whom is the original patient and the other is the induced patient. Therefore, Lasegue and Falret first reported it under the name of "folie à deux" (1877). Occasionally, there are reports of more than two patients, which are called triadic psychosis (folie à trois) or quadruple psychosis (folie à quatre).