The deaths of 168 patients while on drug treatments were reported to the country's medicines' watchdog last year.
They were among 2,884 suspected adverse reaction reports to the Health Products Regulatory Authority (HPRA).
The agency's annual report said suspected adverse reactions were associated with a range of different medicines and in many of the cases reports involved a number of medicines used at the same time.
A spokeswoman said: "The majority of reports received in relation to the medicines tabulated were associated with medicines where the HPRA request or stress the need for close monitoring of patients and reporting of their experience with treatment.
"This may include reporting of events not directly related to a medicine, but occurring in the context of treatment and may be related to the underlying condition(s)."
Medicines most frequently reported include monoclonal antibodies - used in the management of severe debilitating autoimmune disorders, cancer treatment, and in the prevention of transplant rejection.
Others included medicines used in patient support and monitoring programmes for patients with conditions like multiple sclerosis.
In many cases patients had significant underlying illnesses and were treated with multiple medicines or surgery which may have contributed to the outcome.
In many of these cases the disease progressed and the patients had complications unrelated to medicine.