Dublin City Council planners said there was an "overconcentration of social support services in the Dublin 8 area".
It said the planned facility for heroin users at Merchant's Quay would undermine the local community and efforts to develop tourism there.
The decision chimes with the objections of locals and businesses in the area.
It has already been welcomed by Independent councillor Cieran Perry.
However, Merchants Quay Ireland (MQI) has today said the decision "will put lives at risk".
Paula Byrne, CEO of the national homeless and drugs charity, said: “This decision by Dublin City Council is deeply disappointing. With one person a day in Ireland dying of a drug overdose, it will put vulnerable lives at greater risk.
Source: Irish Examiner, 26th July 2019