Pathological lying is defined as telling lies to the point they are persistent, extremely exaggerated and often told without a discernible reward. Psychiatrists have not given pathological lying the title of a true mental disorder as of yet, though this behavior is suggestive of a mental disturbance. Pathological liars are often motivated by low self-esteem to spin a web of lies that make them appear more important or to garner attention from others. Confronting someone you know regarding their pathological lying is a difficult proposition and should be carefully planned.
Learn all you can about pathological lying and what motivates the behavior to better understand the person. This will allow you to confront her in an educated manner when you are ready.
Discern whether the person is actually a pathological liar. Many people fib often, but a pathological liar is one who lies most of the time. Pathological liars, for example, create whole histories that are fiction rather than just telling a little white lie to get out of a social engagement.
Listen to the individual closely. Stop him when he says something bizarre and ask him how it can be true. You can also catch him in small contradictions, which you can question. Do not, however, try to confront him with the “big” stuff at this point.
Reassure your friend that she does not have to be anything she’s not to impress you. Let her know you value her just as she is. If you really don’t like the person due to the lying then stay away from her.
Decide whether the relationship with the pathological liar is too toxic for you to handle. Pathological liars can overcome the propensity to lie, but it takes willingness and, usually, therapy, so to be a friend you need to be there for the long run. Often though, the person does not want help, at which point you need to make a clean break to keep from being hurt.
Talk to your friend about getting professional help once you have proven to him that you have his best interests at heart. You will likely have to confront him with “proof” of his lies to get him to admit he has a problem (and even then he may not).
Make your friend accountable for what she says once she is undergoing therapy. Help her overcome her “need” to lie by assuring her the truth is enough.