Doctors at Spire Bristol Hospital inserted a number of needles in the Doctor Who and Torchwood star's neck.
He told his 1.4 million followers: "Procedure done. It was a bit uncomfortable."
Barrowman, 52, was forced to cancel a string of performances after falling ill on Saturday.
In a post from before the procedure he explained that he was suffering from a facet joint injury, a painful arthritis-like condition, and that he needed a series of injections into his neck.
He said: "Had an MRI and they've found the root of the problem which is a C5/6 facet joint injury.
"Hopefully a series of intraspinal injections will reduce inflammation and get me back up & running again in time for Monday's show in Manchester.
"Fortunately Glasgow was able to reschedule us to Tuesday night so I'm looking forward to that too!"
Barrowman was due to kick off his eight-date A Fabulous Christmas tour on Saturday.
The TV star and singer is also due to release a Christmas album of the same name over the festive season.
He will be seen on screens next year when he joins ITV's Dancing On Ice panel as a judge.