The body said there were already a number of warning signs, including a significant rise in heroin seizures across Europe, including Ireland.
The European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) said the amount of heroin seized in Turkey, the main route into Europe, had doubled in the past three years.
In its 2008 annual report, published in Brussels yesterday, the agency said there had been a worrying increase in the number of new heroin addicts seeking treatment across half of Europe, including Ireland.
It said opiate-related deaths were increasing in most countries since 2005, also reflected in Ireland.
EMCDDA director Wolfgang Götz said the slow improvements in recent years in heroin use appeared to have stalled and may now be getting worse.
“We cannot ignore the threat posed by the glut of heroin now available on the world market and the concerns raised by indicators of heroin use. Vigilance is clearly required.”
EMCDDA analyst Paul Griffiths said it was “likely” the doubling of opium production in Afghanistan between 2005 and 2008 would impact on the availability of heroin in Europe.
He said there was a risk that increased availability could lead to higher take-up of the drug.
But he said that while there was “a lot of noise” about heroin, there was a lack of good data.
War-torn Afghanistan accounts for 90% of the world’s opium, from which heroin is manufactured.
Mr Griffiths said there was also the risk of higher purity heroin.
The Health Research Board, which supplied the Irish data, said there had been a rise in new cases of opiate users starting treatment since 2005, with a total of 1,032 new cases in 2007.
It said Ireland had a higher than average rise in the number of heroin seizures, from 763 in 2005 to 1,254 in 2006.
The quantity seized has jumped from 33kg in 2005 to 129kg in 2006, with more than 145kg seized so far in 2008.
The number of heroin deaths in Ireland rose 28 in 2003 to 44 in 2005.
The EMCDDA also expressed concern about the spread of synthetic opiates, particularly Fentanyl, which claimed 70 lives in Estonia in 2006.
Mr Griffiths said it was between 80 and 10,000 times more potent than heroin, and was being mixed with heroin in some countries.