Warren Anthony Scott, 38, admitted plunging a knife into Edward "Eddie" Carter's chest and legs in his mother's Eden home in April 2019.

His defence argues the incident constitutes manslaughter but the Crown has rejected this plea.

Psychiatrist Dr Kerri Eagle told the NSW Supreme Court on Tuesday that there was no hard evidence he was suffering schizophrenic symptoms such as hallucinations or delusions on the day of the stabbing.

Scott often stopped taking his medication for paranoid schizophrenia, diabetes and epilepsy when drinking daily for long stretches, the court has earlier been told.

Witness evidence of him shutting the curtains when police arrived to hide what was going on inside the house and responding to their questions among other actions showed he was cognitively aware and functioning to a degree, she said.

An explanation that he stabbed his uncle because he was owed money was potentially thought up later given similar circumstances in the past had made him cranky, she said.

The psychiatrist said his excessive alcohol consumption may have precipitated a psychosis given his mental state would have deteriorated without his medication, but noted these symptoms wore off the longer he was sober in custody.

Leading up to the incident Scott told treating psychiatrists he had drunk about three to four litres of cask wine a day, but had recently switched to port.

His mother told the court she had seen him drunk "hundreds of times," but never looking so evil or possessed.

Dr Olav Nielssen took this account and others similar as corroborative reports that his state of mind that day arose from his underlying mental illness.

Scott in the past has reported having evil thoughts and that his tongue was controlled by implanted magnets, but did not self-report any of these symptoms at the time of the stabbing, the court was told.

But Dr Neilssen said it was quite probable that he was experiencing such symptoms given he had been off his anti-psychotic medication, and feeling threatened or persecuted and blaming family members.

Before Scott stabbed Mr Carter he lunged at his mother twice before she left the house seeking help.

The trial, before Justice Natalie Adams without a jury, continues.

Australian Associated Press