An inquest was halted midway as questions were raised about drugs given to a Wigan man in hospital.
Coroner John Pollard said he wanted information from an expert about fentanyl, which was given to Mark Morgan before he died.
The 51-year-old was found collapsed at his home on Warrington Road, Abram, on Thursday July 6.
He had an argument with his partner of 35 years, Sue Morgan, the night before and the alarm was raised when he could not be contacted.
The inquest, held at Bolton Coroner’s Court, was told police forced their way inside and found Mr Morgan unconscious.
He was taken to Wigan Infirmary’s A&E department and then treated on the intensive care unit.
But his condition deteriorated and he died on Sunday July 9.
The inquest heard Mr Morgan used to be a heroin addict, but he had not used drugs since 2003.
He had long-standing health issues with hepatitis C and cirrhosis of the liver.
Consultant pathologist Dr Naveen Sharma told the inquest he carried out a post-mortem examination and toxicology tests were done.
He said Mr Morgan’s medical cause of death was thought to be multi-organ failure due to fentanyl and methadone toxicity, with hepatitis C and cirrhosis of the liver noted as other significant conditions.
The inquest heard Mr Morgan was given fentanyl in hospital while he was on a breathing machine.
It was not known why Mr Morgan had methadone in his system.
Dr Sharma said the fentanyl could have built up in his body as his liver and kidneys were not working properly, leading to the high levels.
But Dr Subash Nandalan, a consultant in anaesthesia and intensive care who treated Mr Morgan in hospital, said his death could not have been caused by the fentanyl.
He said the drug depresses breathing, but he was always on a breathing machine in hospital.
He said: “Fentanyl can only kill someone if they are taken off the ventilator.”
Dr Nandalan said fentanyl was a drug used regularly to stop patients fighting the ventilator.
Dr Sharma said he had not been aware that Mr Morgan was on a breathing machine and he did not know how much support that would give.
Miss Morgan asked Dr Nandalan why fentanyl was given when Mr Morgan’s liver was not working and he said it was preferred over morphine.
The coroner also questioned whether fentanyl was needed and why the levels had become high when he was on a machine to clean his blood.
Mr Pollard decided to adjourn the hearing so more information could be obtained.
He said: “I’m not happy with the treatment he has received. I am going to adjourn this inquest for an expert’s report. I have got contrary evidence from two very experienced doctors who I respect greatly.”
Afterwards, Miss Morgan told the Post she had initially feared Mr Morgan had had a drugs overdose.
“Now I want to find out what has happened,” she said.
A date will be fixed for the inquest to resume.