A retired GP gave patients more than five times the recommended dose of a painkilling drug, a court has heard.
Dr Howard Martin arrives at court for his trial for murder
Dr Howard Martin, 71, is accused of murdering Frank Moss, 59, Stanley Weldon and Harry Gittins, both 74, with morphine overdose injections.
Teesside Crown Court heard how Dr Martin injected powerful drugs into his patients' muscles.
Dr Martin, who practised in Newton Aycliffe, but now lives in Penmaenmawr, Conwy, North Wales, denies murder.
He was charged with murder after the men's bodies were exhumed and subjected to forensic tests, the court heard.
Detectives began investigating Dr Martin, of Beach Road, after the family of Mr Gittins contacted them with concerns about his death.
He is accused of murdering Mr Moss, of New Row, Eldon, on 14 March, 2003; Mr Weldon, from Kimberley Street, Coundon, five days later and Mr Gittins, of Newton Aycliffe, on 22 January, 2004.
The jury heard how Dr Martin, had injected the three men with doses of 60mg of morphine - about five or six times the recommended level with respect to their medical conditions.
Dr Peter Robson, a consultant in palliative medicine at St Benedict's Hospice in Sunderland, said it was not common medical practice to inject large doses of powerful drugs directly into a patient's muscles.
He said: "If I was concerned with giving rapid pain relief, such as someone who has had a heart attack, then an injection would be given intravenously, but that is very rare in palliative medicine."
He said morphine would be given orally and if the patient could no longer swallow or was nauseous, then the morphine would be injected into the vein.
The jury had already been told how Dr Martin gave cancer sufferer Frank Moss, 59, three 60mg ampoules of morphine over a 10-hour period because he claimed he was dying.
The jury also heard that Dr Martin kept made-up syringes of large doses of morphine and diamorphine in his medical bag.
Dr John Grenville, an expert in general practice, said he regarded this as a bad thing and stressed he had never seen it done by any other doctor.
He said: "Clearly, once you have taken the needle out of the sterile package you run the risk of the syringe, needle or the contents becoming contaminated in some way and you may give the patient something you would not want to give."
The trial continues.