Customs has seized 33 orders of drugs, which were formerly sold in the controversial head shops that were shut down in 2010, worth an estimated €120,000 over the past year, new figures obtained by the Sunday Independent reveal.
At least 20 of these seizures were of drugs in powder format. These included Pentedrone - a new designer drug with stimulant effects 4MEC - previously reported as an active ingredient in fake Ecstasy pills; Ethylone - a stimulant and psychedelic; and Methylone - a central nervous system stimulant often sold in the form of bath salts.
Since May 2014, a total of 525 pills have been confiscated in 13 seizures.
Almost 200 of these were classed as benzodiazepines - also known as 'benzos', 'roofies' or 'downers'.
Although Revenue revealed that the majority of the powder and pills originated in Asian countries, it could not confirm that they were all bought over the internet.
"The drugs came through the postal system, including express mail and courier services but it is not possible for us to say categorically that the products we seize were ordered online," a Revenue spokesperson told the Sunday Independent.
Revenue's Customs Service detains and seizes products at the point of entry into the State, including seaport and airport, under both Customs and Medicines legislation.
Medicines detained by Customs are passed to the Health Products Regulatory Authority (HPRA).
Revenue also revealed that it has experienced "some Irish citizen involvement" in the trading of these products.
"The method of operation of smugglers continuously changes. We continuously adapt our risk-profiling techniques to identify and detain illegal and unlicensed material entering Ireland," said the Revenue official.
Gary Broderick, director of the SAOL Project - a Dublin north-inner-city-based rehabilitation project for women in recovery from substance abuse - said he was not surprised to hear that large portions of benzos are being seized, as new regulations on the sedatives, which are often prescribed for the treatment of anxiety disorders and insomnia, are being more tightly controlled.
Mr Broderick told the Sunday Independent: "Benzos are not banned but they are highly addictive so you need to have a very good reason to be prescribing them.
"There is a sense that when there is a reduction in the supply of benzos that people don't suddenly want to stop using because they have used them for years and they are afraid of the withdrawals so they will potentially access them illegally."
Mr Broderick, an addiction counsellor, said drug users often depend on benzos and alcohol as a "come down" after smoking weed. Use of the drug has also been implicated in hundreds of deaths in recent years and recreational use of the drug has become increasinly common.
Symptoms of benzo withdrawals include: panic, sleeplessness, physical pain, fear and psychological distress.
Another concern is that users will move on to other drugs if they can't feed their current addictions.
"What tends to happen when you can't access something is you go looking to find them and or you'll take alternatives," Mr Broderick said.
Although Mr Broderick hasn't noticed a rise in people buying former head shop drugs online, he said, "people may well be buying them from somebody else who has bought them online".
Last year, figures from the HSE revealed that the number of people seeking treatment for addiction to benzodiazepines has more than doubled since 2009.
The Department of Health said benzodiazepines are "prescription only" medicines and that the mail-order supply of all prescription medicines "is prohibited" in Ireland.
A spokesman warned: "There are significant public health concerns associated with the purchase of prescription medicines over the internet. There is no guarantee as to the safety, quality or efficacy of medicines purchased via this route."