Doctors at Queen's University, Belfast, tracked the way new drugs for heart disease and stomach ulcers and the way two powerful new antibiotics were used by GPs in the province between 1988 and 1991.
All three types of drug studied offered genuine advances over older drugs for some patients - they were not just copies of existing drugs, the doctors say in the British Medical Journal.
But they were marketed so effectively by the drug companies that they caused 'unjustifiable changes in medical practice,' according to the team led by Dr Hugh McGavock.
Prescribing of the new heart drugs more than doubled. In the ulcer drugs the increase was almost 50 per cent, while prescribing of the new antibiotics rose by 207 per cent.
But the new and powerful antibiotics - ciprofloxacin and cefuroxime - were promoted by the drug companies for routine use when there was 'little justification', the doctors say.
The new antibiotics are more expensive 'but perhaps the most serious consequence is the inevitable development of widespread bacterial resistance and an increasing incidence of side effects from these drugs.
'They may ultimately become ineffective for managing life-threatening illness'.
The new heart drugs cost 30 times more than some of the older preparations used to treat high blood pressure, so if they are prescribed unnecessarily they will waste NHS resources, the doctors say.
They calculate that during the study period, the need for the new drugs may have risen by a fifth as the population aged. But GPs' prescribing of them more than doubled.
The ulcer drugs were also being used extensively, and at some risk to patients, when simple antacids would often have done as well.
'New drugs should not be allowed to replace equally effective, safe, and tolerable established treatments without good cause,' Dr McGavock and his colleagues say.
'Firstly, the safety of the new products remains suspect until sufficient clinical experience is available. Second, new treatments are almost always expensive, sometimes much more expensive than existing treatments.'
The increase in prescribing for the drugs was far greater than the increase in patients needing them. Doctors seemed to be failing to ensure that 'legitimate promotion of new products does not lead to inappropriate and wasteful use'.Reuse content