Nearly 60kg and about 90,000 tablets containing psychoactive substances formerly sold in head shops were confiscated in 2011.
Sources said the scale of the haul highlighted the existence of a significant illegal market, which was replacing in part the massive legal trade in the drugs before their sale was banned in 2010.
Official figures seen by the Irish Examiner show 56,777kg of head shop drugs as well as 89,990 tablets were seized, worth an estimated €2m on the street. A breakdown of the figures includes:
* 30kg of synthetic cannabis, worth over €1m;
* Nearly 8kg of stimulant mephedrone, worth about €274,000;
* 16kg and 87,000 tablets containing other stimulants worth €584,000.
The stimulants mimic the effects of drugs like ecstasy, amphetamine, and cocaine.
Mephedrone was one of the most popular and notorious of drugs sold in head shops and was linked by both drug projects and gardaí to serious health and crime-related problems.
Seizures of other stimulants include: 12kg and almost 23,000 tablets of BZP; more than 20,000 2C-B tablets, which are a relatively new ecstasy-type drug; and 26,000 ephedrine tablets.
There were seizures of a range of other lesser- known stimulant powders and pills including MDPV, TFMPP, and PMAA.
The market for these psychoactive substances is constantly evolving and increasing.
The EU drugs agency reported last April that new psychoactive substances were being detected at a rate of one per week. A total of 49 new substances were reported in 2011, compared to 41 in 2010 and 24 in 2009.
Last month, 10kg of a stimulant drug, MEC (Methylethcathinone), was seized in Dublin. In addition to these newer stimulants, Garda figures also show greater amounts of ecstasy drugs were seized last year.
Over 100,000 MDMA (ecstasy) tablets and nearly 16,000 tablets of a sister drug MDEA were seized.
Garda sources said ecstasy is experiencing a revival since last year, similar to reports elsewhere in Europe.
In relation to prescription medicine illicitly sold on the street or imported, Garda figures show 33kg and more than 290,000 tablets were confiscated last year.
These drugs have a street value of almost €330,000. They include:
* 29kg of anti-anxiety medication and 253,000 tablets, worth €282,000;
* 4kg of sleep medication and almost 41,000 tablets, worth about €45,000.
The former group includes anti-anxiety tablets Diazepam (Valium) and Alprazolam (Xanax) and Phenacetin, pain relief medication.
The latter group mainly comprises of Zopiclone tablets and powder.
Róisín Shortall, junior minister with responsibility for the national drugs strategy, has promised plans by the end of the year to tackle the street sale of prescription tablets.