A disciplinary panel examining the deaths of 18 patients of a former County Durham GP has found his conduct was "below expected standards".
Dr Howard Martin prescribed irresponsibly high levels of morphine, according to the General Medical Council (GMC).
The panel said he did not properly assess the condition of his patients and the doses of drugs required.
Dr Martin was cleared of murdering three of his patients five years ago.
The fitness to practise hearing in Manchester is concerned with the deaths of the 18 patients between 1994 and 2004 at surgeries in Newton Aycliffe, Shildon and Eldon.
The panel said the doses of morphine given to the patients shortly before their deaths were in excess of those necessary to treat pain or distress.
It also heard he acted inappropriately, in one case telling a patient's wife that he would give her husband an injection to send him to "sleep peacefully" and he would "not wake up again".
The woman said Dr Martin told her not to mention this to anyone else as it would make more paperwork for him.
The GMC is expected to make a fitness to practise ruling later.
The former GP did not attend the hearing and in a letter from his solicitor said he had no intention of doing so.
He said he was not prepared to travel from his home in north Wales because his wife, aged in her late 80s, was in poor health.
Dr Martin added that he saw no "practical consequences" in the outcome as he had retired and did not wish to work in medicine again.
In 2005, he was found not guilty of murdering patients Frank Moss, 59, Stanley Weldon, 74 and Harry Gittins, 74, with morphine overdoses.