The Irish Patients Association says people on prescription medicine should be given consent forms to ensure they are warned about possible side effects.
It follows a warning from the HSE to doctors about the dangers of prescribing incorrect dosages of blood-thinning drugs aimed at reducing the risk of stroke.
A health service review shows that 4,000 patients on the drugs had either been prescribed too low a dosage, or had been given other medicines which minimised or counteracted its effects.
Professor Michael Barry of the HSE's Medicines Management Programme says anyone with concerns should contact their GP.