What is preexistent?

Answer 1

Preexisting psychosis means that the psychosis was already present before another factor became involved in altering the person's mental health status.

It is hard to comment directly without more information, but here is an example. A person might have psychosis already as a late teenager. He might then go on and use drugs and this makes the psychosis worse. The mental health worker might say something like "The young person appears to have had a preexisting psychosis that has been exacerbated by substance use".

It would most typically be stated in this way when the mental health worker provides an opinion about whether the psychotic symptoms came first (and in their own right), or whether they emerged as a result of something else.

This is important when making a correct diagnosis, as it can distinguish between (for example) schizophrenia versus substance-induced psychotic disorder.