Someone i know has psychosis and taking anti-psychotic medication. can this explain this mental condition be contributing to his lying which has been prevalent. i don't know if he even thinks he's lying, and may have convinced himself what he is saying is

Psychosis : Psychosis is a serious medical condition that is characterized by loss of contact with reality, delusions and hallucinations. They often have false beliefs about what is going on around them and what is happening to them. Having said that, these people may say things that are untrue (lie) and may not be able to follow medical advice because they can not comprehend their condition. This persons tendency to lie can certainly be related to their medical condition.

This is the problem: Exactly. That is in the nature of psychosis. What we call delusional thinking is precisely to be convinced of wrong ideas, perceptions, memories, etc. If the psychosis is real and active, the individual will lie while believing in the absolute truth of it.