How Can Aggressive Behavior And Slurred Speech Be Managed While On Seroquel?

My son s doctor/therapist has prescribed Seroquel (several months back) for trouble sleeping, anxiety, and palpitations. He is already taking propanolol (prescribed by his internal medicine doctor for palpitations). I am not sure of the Seroquel dosage, but it alarmingly changes his behavior: Aggressive, hostile, inappropriate comments, slurred speech, and, most concerning, utterings of killing himself . Any suggestions? When I ve confronted him, he tells me he is trying to cut back on taking it because one can t just get off this medication. He is 33 years old and has a history of addiction, although has been sober (I think) for about 4 years. I have urged him to tell the prescribing doctor, but not sure he will.