We have a friend who is a 23 year old male. His affect has become very flat over the past 2 years. He tends to be spacey and zone out. His responses tend to be delayed for a couple of seconds. He used to be very outgoing and fun and spontaneous but no longer is. He possibly had a psychotic break about a year and a half ago. He does not seem delusional but has trouble staying engaged in a conversation for a long period of time ie a dinner conversation. Also, very quiet at parties where he never use to be.
Hello thanks for asking information you provided is not sufficient to make a clear-cut diagnosis, but the symptoms suggest some mood disturbance most probably depressive disorder. The symptoms like flat affect, poor social interaction, remaining silent in social situations etc. could be due to depression. You have mentioned that he doesn't appear to be delusional and also not violent, so possibility of any underlying psychosis is unlikely. If he is taking any Chat Doctor.  Cannabis derivatives like marijuana could precipitate psychosis and may lead to symptoms like flat affect, poor motivation etc. So please talk with a psychiatrist and take appointment for him. Thanks and Take care