An emergency session of parliament has been called to pass legislation to recriminalise the drugs, The Journal has reported. It is believed possession will remain legal until Thursday, when the new laws will come into effect.
The case was brought to appeal by a Lithuanian national arrested over possession of methylethcathinone in 2012. Following his conviction, the man's lawyers argued that it would be unfair to be in possession of a drug that was legal one day and illegal the next.
Drugs covered by section 2(2) of the law included crystal meth, ketamine, MDMA and magic mushrooms.
In recent years, Ireland has seen a growth in retailers which sell psychoactive substances and drug paraphenalia, known as 'headshops'. This has resulted in Ireland's police force struggling to keep up with the introduction of new drugs available to the public.
Dozens of previous convictions are now under question, according to the country's health minister, Leo Varadkar:
"I'm told it's dozens, but I can't say for certain because what they'll have to do now is go thought each individual case and see if the people in question were charged just under this section of the act, or if they were charged with other acts as well."
Politicians had been alerted to the potential ruling for the past week, keeping the situation under tight wraps from the media.
