Nick Reiner Became Homicidal After Schizoaffective Meds Were Changed

Nick Reiner's mental breakdown in the weeks leading up to the murders of his parents, Rob and Michele Reiner, is directly tied to a head-scratching decision by doctors to change the meds he was taking for his mental illness ... sources with direct knowledge tell TMZ.

TMZ has a new documentary -- "TMZ Investigates: The Reiner Murders: What Really Happened" -- airing Friday at 8 PM ET on FOX and dropping on HULU Saturday. We explain in the doc, Nick was diagnosed around 2020 with schizoaffective disorder ... a condition that manifests itself with schizophrenia symptoms -- including delusions, hallucinations, and disorganized thinking -- and mood disorder symptoms, including mania and severe depression.

Our sources say a month before the murders, Nick was stable on his meds for schizoaffective disorder ... we're told the meds were working just fine. For some reason, his doctors decided to change the meds. Our sources would not say why doctors made that decision ... only that we would be shocked to learn the reason, which we're told makes no sense.

We're told the change in meds sent Nick into a spiral. He became agitated, erratic, and increasingly dangerous. Our sources say Rob and Michele were alarmed at what they were seeing, but didn't know what to do.

Our sources say by the time of the murders, Nick had a complete break from reality. We're told doctors did not attempt to place Nick under a psychiatric hold while they tried to adjust the meds and stabilize him.

This, we're told, may be the heart of Nick's defense -- that doctors sent Nick on a path that made him legally insane. Under California law ... a defendant does not have to show he didn't know the difference between right and wrong to use the insanity defense ... only that he didn't understand the nature and quality of his act.