What OTHER drugs? Opiods, Mushrooms, etc.. Some drugs (I have heard) do cause hallucinations, etc.. when coming down. I think your son needs to see a doctor who specializes in multiple addiction withdrawals.
I can tell you that the lorazepam, is a drug best NOT stopped cold-turkey, but not sure how much he took of that either.
Good luck with your son, but your question is a difficult one to answer due to several unknowns.
Is he seeing a doctor and/or therapist?
If you are saying he is having psychotic behavior that does not sound (to me ) as something caused by withdrawl .Slight paranoia is one thing highly paranoid is another .There may be an underlying problem that he was using the drugs to mask ? Do you think that is possible.