Gangland killer Gary Campion has come out of a coma after being found unresponsive last week in his cell in Mountjoy Prison.
Campion (32), who was caught with 73 bags of heroin in Limerick Prison nine years ago, woke up at the Mater Hospital on Saturday morning "better than when he went in", a prison source said.
Campion, from Moyross, is serving two life sentences, for the 2002 murder of innocent nightclub security doorman Brian Fitzgerald and the 2006 gangland murder of 'Fat Frankie' Ryan.
He was rushed by ambulance to the Mater Hospital from Mountjoy last Thursday morning.
A garda probe and a separate prison investigation will be launched into the circumstances that led to Campion nearly dying.
An Irish Prison Service source said Campion was under special observation when he collapsed in the cell.
"We believe he received a package earlier in the week on a visit. It was either hidden about his person or he ingested it," the source said.
"We believe a bag of drugs may have burst inside him."
The source said Campion, who has more than 40 previous convictions, was being held in a "close supervision cell" when he lost consciousness.
The killer, who was the first person in Ireland to be convicted of two gangland murders, arrived at hospital in a critical condition and placed in an induced coma.
Sources at Mountjoy said they were shocked when Campion woke up "apparently feeling refreshed".
"He was on his last legs. It looked so bad for him that his family were immediately notified that they may be facing his imminent departure," the source said.
Until he was jailed for murder, the father-of-two was a hitman for hire for feuding criminal gangs in Limerick.
He was found guilty of murdering nightclub doorman Brian Fitzgerald on November 15, 2007, and received another life sentence on May 28, 2009, for the murder of Ryan.
In 2009 he was given a four-year sentence at Limerick Circuit Court after he was convicted of having 73 ready-for-sale bags of heroin in his cell in Limerick Prison.