There were 738 patients harmed in medication-related incidents in HSE services last year, according to new figures.
Of those, 732 cases were listed as causing minor or moderate harm while six were determined to be extreme.
Five of these resulted in death.
A total of 10,400 medicine-related incidents, or near misses, were recorded.
More than 7,150 incidents reached a patient but with no harm, or negligible harm.
Over 2,540 were classified as near misses, meaning they did not reach a patient.
A medication incident is a preventable event which may result in a patient being harmed while medication is in the control of a healthcare professional.
The details are contained in a HSE response to a parliamentary question from Aontú leader Peadar Tóibín.
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It said that in terms of definition, the severity of 'extreme' with medication errors, is when an incident leads to permanent incapacity (including psychosocial), or death.
State Claims Agency data shows that the most common medication incident was an omitted or delayed medication dose.
The public health service deals with around two million inpatient and day case treatments every year and almost the same number of emergency department cases.
The HSE said that its Patient Safety Strategy includes reducing medication-related harm as one of the common causes of harm, a priority area for safety improvement.
It said that improvements are introduced on a local, regional and national basis in order to reduce the risk of harm with medication.
The HSE said that a Polypharmacy key performance indicator was introduced this year.
It tracks the proportion of people aged 65 years and older prescribed ten or more regular medications, as an indicator of an increased likelihood of potentially inappropriate medication.
The Health Information and Quality Authority conducts inspections in public hospitals to improve patient safety in relation to medication use.
