Folie à deux (French for “madness of two”) is a rare psychiatric condition in which a delusional belief transfers from one person to another within a close relationship. One person develops a genuine psychotic delusion, and a second person, through prolonged intimate contact, comes to share that same delusion as though it were their own. The condition has also been called shared psychotic disorder, though modern diagnostic manuals have largely folded it into broader categories of delusional disorders.
How the Delusion Spreads
The dynamic always involves two distinct roles. The primary person (sometimes called the “inducer”) is the one who develops a delusion independently, often rooted in a condition like schizophrenia or delusional disorder. This person typically holds a dominant position in the relationship, whether through personality, authority, or sheer force of conviction.
The secondary person (the “induced”) adopts the delusion over time. They don’t arrive at it on their own. Instead, the closeness of the relationship and the persuasiveness of the primary person gradually erode their ability to evaluate the belief critically. Secondary partners tend to be more impressionable, sometimes due to a dependent personality, limited social connections, or cognitive vulnerability. Factors like geographic isolation, language barriers, and socioeconomic hardship make the dynamic more likely because they shrink the secondary person’s world down to the relationship itself.
Which Relationships Are Affected
Folie à deux occurs most often between people who live together and share deep emotional bonds. Mother-daughter pairs are among the most frequently documented, but it also appears between spouses, siblings, and parents and children of any combination. In rare cases, it extends beyond two people to entire families, sometimes called folie à famille. The common thread is always a tight, often isolated unit where one person’s reality becomes the dominant narrative and there are few outside perspectives to challenge it.
The condition is considered rare, though its true prevalence is unclear. Most of what clinicians know comes from individual case reports rather than large-scale studies, which makes it difficult to estimate how often it actually occurs. It may also go underreported because the secondary person’s delusions can resolve before they ever reach clinical attention.
The Four Recognized Subtypes
Not all cases of folie à deux work the same way. Clinicians have identified four distinct patterns, and they differ in how deeply the delusion takes root in the secondary person.
- Folie imposée (imposed psychosis): The most straightforward form. Delusions transfer from the primary person to a previously healthy secondary person. Once the two are separated, the secondary person’s delusions typically disappear on their own.
- Folie communiquée (communicated psychosis): Similar to folie imposée, but the secondary person resists the delusion for a long time before eventually accepting it. Because the belief becomes more deeply internalized, separation alone may not resolve it. The secondary person can maintain the delusion even after the primary person is no longer present.
- Folie induite (induced psychosis): The secondary person, who may already have a psychotic condition of their own, absorbs new delusions from the primary person and then generates additional original delusions. Separation is not effective here because the secondary person has essentially built upon the shared belief system independently.
- Folie simultanée (simultaneous psychosis): Both individuals develop psychotic symptoms at roughly the same time, often in the context of a shared genetic vulnerability. Both require direct treatment.
What Treatment Looks Like
The first and most important step is physical separation of the two people involved. For many secondary partners, particularly in cases of folie imposée, this alone is enough. Once removed from the primary person’s influence and exposed to other perspectives, the shared delusion fades and they return to their baseline mental state. This can happen relatively quickly, though no universal timeline applies.
Separation doesn’t always work. One study found that when the secondary partner had a personality disorder, only about 40% recovered after being separated from the primary person. The recovery rate dropped even further when the secondary partner had a prior diagnosis of schizophrenia. In these cases, and in folie induite or folie simultanée, both partners typically need medication to manage psychotic symptoms.
The primary person is treated the same way as anyone with a standalone delusional disorder, usually with antipsychotic medication. For the secondary person, treatment depends on how deeply the delusion has taken hold. If separation resolves the symptoms, ongoing psychiatric medication may not be necessary. If delusions persist, antipsychotic drugs are added. Therapy aimed at increasing personal autonomy and rebuilding social connections outside the relationship is also a key part of recovery, since isolation is often what allowed the dynamic to develop in the first place.
Why Isolation Is the Key Risk Factor
Folie à deux is fundamentally a disorder of context. It thrives in environments where two people are cut off from the outside world. When you have no coworkers, neighbors, friends, or family members offering a reality check, the most persuasive person in the room defines what’s real. Language barriers that prevent someone from communicating with people outside the household, rural settings with limited social infrastructure, and financial dependence that makes leaving the relationship difficult all create the conditions where shared delusions can take root.
This is also why the condition tends to resolve when the environment changes. Reintroducing the secondary person to a broader social world, where other people do not share the delusion, is often the most powerful corrective. The delusion, which felt airtight inside the closed system of the relationship, simply can’t survive contact with a wider reality.