Dr Stephen Monks told the Central Criminal Court that he would "strongly disagree" that Michael McDonald suffered from the mental illness bipolar defective disorder.
Fergal Kavanagh, for McDonald, said that a psychiatrist who has examined McDonald since 1998 will give evidence that he suffers from the disorder.
"I can only give my opinion but I would strongly disagree. There is no evidence of bipolar defective disorder," Dr Monks told the jury.
McDonald (51) of Barnhill, Castledermot, has pleaded not guilty to the murder of Breda Cummins on May 13, 2010, at Michael Dooley Terrace, Athy.
He has further pleaded not guilty to assault causing harm to John Lawlor (44) of Pearse Terrace, Castledermot, at Michael Dooley Terrace on the same date.
McDonald has admitted to the manslaughter of the mother-of-one but this plea has not been accepted by the Director of Public Prosecutions.
Mr Kavanagh put it to Dr Monks that McDonald, who had admitted himself numerous times between October 1998 and March 2006 at Naas General Hospital for psychiatric reviews, feels to a certain degree he may have a mental illness and believed in 2006 he did in fact have a mental illness and believed he would harm himself and others.
"To diagnose depression when there is a history of heavy drinking is dubious in my mind," said Dr Monks. "The important thing is to get a clearer picture once alcohol is removed from the system."
Dr Monks also said that despite in 2003 McDonald telling a doctor that he received messages from the Devil to kill himself, there was no record of these symptoms persisting, but that reports of psychiatric symptoms were from the withdrawal of alcohol.
He said that after analysing four of McDonald's diaries which included entries such as "terror being bound in spells and not knowing how to get out," "stolen child trying to find ones years and the spells," "purple heart on a ship, tapping into Mars and Jupiter, be the boss of yourself taking off like a mad March hare," and "body red, blood wine, drink own blood, eat own flesh," and "angel waiting on me, trying to get inner junkie to let go of outer monkey," that he did not find these as ramblings of someone experiencing a mental breakdown and the writings did not convince him of someone who has a mental illness.
"The themes of his diary entries seem to be exploring spiritual and philosophical beliefs. He is an aspiring writer but nothing in the diaries gave me an indication of mental illness but the exploration of philosophical beliefs," said Dr Monks.
"It is impossible to draw any conclusions as to what he was thinking at the time of writing these without having spoken to him and examined him at the time," he continued.
Mr Kavanagh asked Dr Monks if it was a feature of bipolar disorder that McDonald was begging for help, and gets sober but doesn't take anti-depression medication, to which Dr Monks replied "it is not behaviour specific to mental illness."
He put it to Dr Monks that when McDonald told a doctor that he was "preventing American and British forces from invading Iraq because of magical powers" that this is down to drinking excessively, Dr Monks said "if these thoughts persisted outside of alcohol use then it would be of clinical concern."
Dr Monks said he did not find any material which was a cause of concern of McDonald being mentally unstable.
The trial continues.