The refusal by pharmacies to dispense methadone in a row over profit margins will "inevitably" lead to some addicts returning to heroin-use, according to the director of the State's largest voluntary drug treatment centre.
Tony Geoghegan of the Merchant's Quay project said today that while the contingency plan for dispensing methadone normally given out by pharmacies appears sound, its effectiveness will only emerge over the coming days.
Mr Geoghegan that those who have recently been registered on a community methadone scheme are particularly vulnerable.
"There's already some anxiety being expressed to us and there's no doubt that it will destabilise progress that's been made.
"It is inevitable that some people are going to fall through the cracks," Mr Geoghegan told ireland.com.
Among the problems for the 3,000 or so affected users, will be the need to produce photographic identification and the change in the time they get their methadone. Some people normally take their methadone early in the day but will now have to wait until the evening because of the new arrangements.
"If someone has trouble accessing their methadone they will inevitable turn to something else," said Mr Geoghegan.
This increases the likelihood of overdoses because in some cases the addict's tolerance for heroin will have lessened, he added.
A HSE spokesman also said there was "a significant clinical risk of overdose" to clients who reverted to heroin instead of methadone - the synthetic substance used to treat withdrawal symptoms from heroin addiction.
Sinn Féin's Aongus Ó Snodaigh said referring users to clinics was "the equivalent of sending a recovering alcoholic into a public house to have his anti-booze dispensed".
Around 140 members of the Irish Pharmaceutical Union (IPU) in Dublin began refusing to participate in the community methadone dispensing scheme today. Pharmacists concern over the security for their premises has been a long-running source anger and has exacerbated the dispute.
The HSE has put arrangements in place in 11 HSE premises around the city, and it has set up a drug helpline (1800-459459) for clients on the methadone-maintenance programme.