Confusion over the branding of drugs could mean some patients in Northern Ireland are renewing medications they do not need, a senior doctor has said.
Dr Alan Stout of the British Medical Association (BMA) said the issue related to changes in how medication was presented.
GPs are advised to prescribe the cheapest version of a particular drug available at a given time.
Patients can therefore see changes to branding and packaging.
"We are encouraged to use what is known as branded generic, which are the cheapest, most cost-effective version of that medication," said Dr Stout, chair of the BMA's Northern Ireland GP Committee.
"The confusion can arise because the cheapest version can keep on changing.
"So the same patient might remain on the same medication, but it looks different every time they get it."
Dr Stout explained the generic version of a drug is almost always the cheapest, but there are exceptions.
"On occasion, there is a bulk purchase of a branded version which brings the cost down even more, and practices are then asked to change all the prescriptions to this one," he said.
Dr Stout said over ordering was not a common occurrence, but an issue for patients who were "more elderly or on a long list of medication".
Appearing before the Northern Ireland Affairs Committee last week, the permanent secretary in the Department of Health, Richard Pengelly, said patients taking a variety of medication for different conditions may renew prescriptions they do not need.
"It is much easier to ring up and say 'can I have my repeat medication' than rather to say 'I only need that one and that one'. Some of these drugs are unpronounceable," he told the committee.
Mr Pengelly said he had been told about a community pharmacist's client who had died, leaving behind between £6,000 and £10,000 worth of unopened medication in their home.
Once medication has left a pharmacy it cannot be recycled, even if it has not been opened.
Mr Pengelly added there was a "debate that needs to be had" on the possibility of reintroducing prescription charges in Northern Ireland.
Prescriptions in Northern Ireland have been free since 2010, something which is also the case in Wales and Scotland.
Patients in England are required to pay £8.50 per item.