The study of more than 600 patients, by experts at the department of geriatric medicine in Cork University Hospital (CUH), showed that 52% were receiving drugs that could potentially counteract another medicine the patient was taking for a different ailment.

In 57% of cases studied, the team found that GPs had not prescribed a medicine considered to be the best to treat a specific ailment.

One of the experts working on the study, Dr Denis O'Mahony, a senior lecturer at CUH's department of medicine and a consultant in geriatric medicine, said most instances of inappropriate prescribing related to primary care.

"For the most part, it is coming from the primary care sector . . . general practitioners, " he said. GPs were responsible for 85% to 90% of the cases of inappropriate prescribing uncovered in the study, he said.

The study will be published in the UK's Journal of Clinical Pharmacy and Therapeutics later this month. It will open up debate over the prescription by GPs of medicine for the elderly, particularly for those on multiple medications.

"The instances we discovered varied in severity from what might be appropriately described as being minor in some cases and major in others. The cases of highest severity include instances of inappropriate prescription that may result in patient fatality, " O'Mahony said.

Dr James Stacey, executive officer with the Association of General Practitioners (AGP), said that the study showed "what most GPs already knew to be true. . . that doctors are lucky if they get prescriptions right in more than half of cases.

Every doctor, be they GP or consultant, will admit that in complex cases, finding the correct treatment for a person on a range of other medication is more art than science. It is often trial and error."