Around 70,000 adults have bought medicines online, according to a new survey from the Health Products Regulatory Authority.
The main reasons are lower prices, convenience and greater privacy.
The authority says that while the authenticity and safety of medicines available via the internet is a concern for two-thirds of people, almost a third were surprised to learn that it is illegal to buy prescription medicines online.
Also it has expressed concern that 8% of adults, which would represent 267,000 people, say they would consider buying medicines online in the future.
The survey shows that the influence of the internet as a channel of health information is significant with one in four using it to source information on medicines.
The survey found that 70% of people use it to research a particular health problem, 46% research types of medicines for particular conditions and 39% use it to diagnose symptoms.
There has been a substantial growth in confidence and understanding of generic medicines.
However, few people are reading product information for over the counter medicines and prescription medicines.
GPs and pharmacists remain the most trusted sources of advice on medicines.
The survey of 1,000 adults was undertaken for the HPRA by market researchers Behaviour & Attitudes.
The Irish Pharmaceutical Healthcare Association has said that medicines should be dispensed through the proper channels and that patients should be purchasing the ones their doctor has prescribed for them.
Speaking to RTÉ News, the association's CEO Oliver O'Connor said there were laws and regulations in place to make sure that it happens.
He added that the IPHA does not distinguish between any particular pharmacist so long as they are all following the regulations.
Mr O'Connor said the regulations were in place to ensure patient safety.
The Health Products Regulatory Authority (HPRA) also warned of the dangers of buying medicines online, saying there is no guarantee of their quality, safety or effectiveness.
HPRA Chief Executive Lorraine Nolan said testing of these products has shown they may not contain the active ingredient or may contain too much of the active ingredient, both of which can have serious consequences.
Ms Nolan urged consumers not to put their health at risk by sourcing medication through unregulated sources, saying there was no price that could be put on a person's health.