A mythomaniac is a person who lies compulsively and excessively, often without a clear reason. The term comes from “mythomania,” an older clinical name for what psychiatrists now more commonly call pathological lying or pseudologia fantastica. These terms are generally used interchangeably. Unlike ordinary liars who deceive to get something specific, mythomaniacs tell falsehoods that are wildly disproportionate to any apparent goal, and the pattern can persist for years or even a lifetime.
How Pathological Lying Differs From Normal Lying
Everyone lies sometimes. But pathological lying has a distinct quality: the lies are extensive, complicated, and often serve no obvious purpose. One of the clearest research findings is that pathological liars report telling lies “for no specific reason” at significantly higher rates than other people. Their lies also tend to snowball. A small fabrication becomes the foundation for a larger story, which spawns more stories, until the person is maintaining an elaborate fictional version of their life. In studies comparing pathological liars with non-pathological liars, the pathological group scored dramatically higher on measures of lie escalation, meaning their untruths reliably grew from one initial falsehood into something much bigger.
The classic clinical definition, first formulated over a century ago, describes the behavior as “falsification entirely disproportionate to any discernible end in view, may be extensive and very complicated, manifesting over a period of years or even a lifetime.” That disproportionality is the hallmark. A person who lies to avoid punishment or gain money is calculating. A mythomaniac fabricates stories that don’t clearly benefit them at all.
How Common It Is
Pathological lying is not as rare as you might assume. Research published in the American Journal of Psychotherapy estimated its prevalence at 8% to 13% of the general population. That’s a surprisingly wide slice of people, though it includes a range of severity. Some individuals lie compulsively but cause relatively limited harm; others build entire identities around fabrications.
What Drives the Behavior
At its root, mythomania appears strongly connected to a fragile sense of self. Multiple case studies point to low self-esteem as a core driver, with the lies functioning as a way to compensate for deep feelings of shame or inadequacy. The person isn’t simply trying to impress others. They’re constructing a version of themselves that feels more tolerable to inhabit.
Childhood experiences play a significant role. Trauma, neglect, and dysfunctional family dynamics are all recognized as environmental factors that contribute to the development of pathological lying. A child who learns early that reality is painful or that the truth brings punishment may develop lying as an automatic coping strategy, one that eventually becomes deeply ingrained.
The DSM-5, psychiatry’s main diagnostic manual, does not list pathological lying as its own standalone diagnosis. Instead, it recognizes the behavior as a feature of several personality disorders, particularly the “cluster B” types: narcissistic, antisocial, histrionic, and borderline personality disorders. It’s also associated with PTSD. The reason it shows up across these different conditions is that the lying serves different psychological functions depending on the underlying issue. Someone with narcissistic traits lies to inflate their accomplishments and draw admiration. Someone with borderline traits lies to maintain relationships or avoid abandonment. Someone with antisocial traits lies to manipulate others for personal gain.
What Happens in the Brain
Brain imaging research has found structural differences in the brains of pathological liars. A study published in the British Journal of Psychiatry used MRI scans to compare the brains of pathological liars with those of both antisocial individuals who didn’t lie pathologically and healthy controls. The liars had 23% to 36% more connective tissue (white matter) in the front of their brains, specifically in areas involved in decision-making, social behavior, and impulse control. This extra wiring was found in the lower and middle portions of the prefrontal cortex but not the upper portion.
What does this mean practically? White matter is the brain’s cabling. It connects different regions and allows information to travel quickly between them. Having more of it in the prefrontal cortex could make it easier to weave together complex narratives on the fly, linking ideas, memories, and fabrications faster than the average person. Importantly, the liars showed no difference in gray matter, the tissue responsible for processing. So it’s not that they think differently in some fundamental way. They may simply have a brain that’s better wired for the mechanics of deception.
How It Affects Relationships
Living with or close to a mythomaniac is exhausting. In the early stages of a relationship, partners and friends often sense that something is off but can’t pinpoint what. The stories are detailed and confident, so doubts feel unreasonable. Over time, as inconsistencies pile up, the experience shifts to frustration, anger, hurt, and confusion. People close to pathological liars frequently describe a feeling similar to being gaslit, constantly questioning their own sense of reality because the liar is so convincing and so persistent.
Trust becomes nearly impossible to build or maintain. Even when a pathological liar is caught, they may double down, revise the story, or generate a new fabrication to explain the old one. This cycle can create genuinely toxic dynamics in friendships, romantic partnerships, and family relationships. For the people around them, the emotional toll is real: they may withdraw from the relationship entirely or develop anxiety about their own ability to judge what’s true.
How Mythomania Differs From Related Conditions
Several psychiatric conditions involve some form of deception, and it helps to understand how they’re distinct. Confabulation, which occurs in people with certain types of brain damage or memory disorders, involves creating false memories to fill gaps. The person genuinely believes what they’re saying. Malingering is the deliberate faking of illness or symptoms for a concrete external reward, like disability payments or avoiding criminal charges. Factitious disorder involves fabricating or inducing illness in yourself (or someone in your care) to receive attention in a medical setting.
Pathological lying sits in its own territory. The mythomaniac may partially believe their own stories or may know full well that they’re lying. The lies aren’t anchored to one specific goal like financial gain or medical attention. They’re broader, more varied, and often self-aggrandizing in ways that don’t lead to any tangible payoff. Psychological testing can help clinicians distinguish between these overlapping conditions, particularly when it’s unclear whether someone is experiencing psychotic delusions, malingering for gain, or lying compulsively as part of their personality structure.
Treatment Options
Treating pathological lying is genuinely difficult, in part because the behavior itself undermines the therapeutic relationship. A therapist relies on honest self-reporting to understand what a client is experiencing, and a pathological liar may fabricate or distort information even in therapy, sometimes without being fully aware they’re doing it.
Because mythomania isn’t a standalone diagnosis, treatment typically focuses on the underlying condition driving the behavior. For someone with narcissistic traits, therapy might work on building a more stable sense of self-worth that doesn’t depend on fabricated achievements. For someone whose lying is rooted in childhood trauma, processing those experiences can reduce the need for the protective fiction. Cognitive behavioral approaches can help a person recognize the automatic thought patterns that trigger lying and develop alternative responses, but this requires the person to first acknowledge the problem, which is often the biggest hurdle.
Progress tends to be slow. The lying pattern is usually deeply embedded by the time someone reaches treatment, and the person may have spent years or decades reinforcing it. Motivation matters enormously. People who enter therapy because a relationship is falling apart or because they’ve faced serious consequences from their lying tend to engage more honestly than those who are pressured into it by others.