More than half of drug addicts are now abusing prescription drugs, according to a new survey by a drug treatment group.
The Ana Liffey Drug Project found 56% of a sample had used prescription drugs within the past week.
And prescription drugs were found to be present in two-thirds of the 348 overdose deaths in 2015 the last night year for which statistics are available.
The drugs involved are benzodiazepines which are prescribed as tranquilisers, z-drugs used as sleeping tablets and pregabalin a painkilling and anti anxiety drug used to treat a number of medical conditions including epilepsy.
Pregabalin-related deaths have increased from 26 in 2014 to 44 in 2015.
CEO of the Ana Liffey Drug Project Tony Duffin said the drugs are obtained through prescriptions, imported through the internet from India and China, but are also increasingly counterfeit tablets made by criminal gangs.
He said he has seen bars of drugs marked Xanax which have been pressed in Dublin and Limerick.
Ana Liffey has launched a leaflet campaign aimed at drug users in Dublin's north inner-city titled 'Do you use street drugs?' with advice on how to avoid fatal overdoses.
"I know it will be shocking to think that some people in Dublin's north inner-city are taking whole trays of tablets in one go".
"This has implications for their health and their behaviour, we must do more to respond to this".
In particular the leaflet warns people not to suddenly stop taking the drugs as this can cause convulsions known as 'benzo fits'.