The fire engulfed the three premises in Capel Street this morning and prompted a complete evacuation of surrounding buildings.
The entire street was closed to traffic, causing severe traffic disruption during the morning rush hour.
Five units of Dublin Fire Brigade, as well as a ladder unit and an ambulance, were sent to the scene.
The alarm was raised after smoke was spotted pouring into the street.
The blaze destroyed the Nirvana head shop, as well as the Utopia adult store and a souvenir shop on either side of the head shop.
It is unclear what caused the blaze and gardai were initiating an investigation into the circumstances of the fire.
The burning premises were situated near the quays end of Capel Street, and large plumes of smoke billowed out onto surrounding streets and the quays during the blaze.
Fire crews with breathing apparatus tackled the fire from the street as well as inside the burning buildings.
A garda spokesman told the Herald the emergency services were alerted about the blaze at 6.25am. He confirmed that an investigation was underway.
Long tailbacks of traffic were caused on the city's northside during the blaze as Capel Street is a busy commuting route for people travelling to work.
A Dublin Fire Brigade spokesman said that five pump vehicles were sent to the scene along with an aerial appliance to enable the fire to be fought from a height, if necessary. Some 25 firefighters were active at the scene, he said.
He said the fire was brought under control but teams needed to remain at the scene for a considerable time.