An inquest into the death of a Launceston aged care resident who was given a morphine overdose has heard it is likely pre-existing illnesses caused his death.

Stanley Valentine Whiley, 67, had heart disease and suffered his second stroke on the night he died at the Tamar Park nursing home in March 2010.

Newly-registered nurse Julie Lord, who had only done one night shift before, was the only nurse on duty and had never administered morphine.

Mr Whiley died within five hours of Ms Lord giving him 25 milligrams of morphine, instead of the prescribed 2.5 milligrams.

Forensic clinical physician Dr Ross Ulman told the hearing it was more probable Mr Whiley's illnesses caused his death than the morphine.

Dr Ulman said that if the morphine had any effect at all on the timing of Mr Whiley's death, it may have brought it forward by a few hours.

Dr Ulman said Ms Lord was inadequately supervised.