An inquiry was ordered by the coroner after Mrs Rowbottom's devoted son, Derek, 44, confessed to administering two huge doses of the drug.
Mr Rowbottom, of Ashton-under-Lyne, was interviewed by police after his mother's death in North Manchester General Hospital last month.
Mrs Rowbottom, of Moston, who had spent six weeks at the hospital unable to eat, drink or move, died shortly after her son was spotted by nurses administering a double dose of the pain-killing drug diamorphine.
He later said: "I just wanted to ease her pain. She would have done the same for me. If the law prevents you from helping someone that you dearly love to rest in peace, it just wants changing," he said.
A CPS spokesman said the matter was "under consideration".Reuse content