Adam Sayers, who is banned from a number of businesses in his local area, entered a One Stop Shop in Sunderland in February.
Newcastle Crown Court heard the worker approached the 34-year-old when he noticed him acting suspiciously in one of the aisles.
Prosecutor Matthew Bean said: "The defendant was made subject to a criminal behaviour order in 2020 preventing him from entering a number of specified retail premises.
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"He is prolific shoplifter and is known to many members of staff in shops in the area where he lives.
"On the 9th of February this year just before 4pm, he entered the One Stop Shop in Roker.
"The complainant described being suspicious of the defendant's behaviour as he observed him on CCTV.
"He was seen to take a number of cases of chocolate bars."
The court heard that the manager then decided to walk up to Sayers, asking him to leave due to his concerns.
After telling the defendant that the police had been notified, Sayers pulled out the syringe and pointed it towards his victim before he was arrested a short while later.
In an impact statement, the manager said: "This incident has left me feeling anxious.
"I feel as if I'm looking over my shoulder. No one should have to put up with this when at work."
Sayers, of Franklin Street, Sunderland, was already serving a prison licence period at the time before pleading guilty to robbery.
Matthew Hopkins, mitigating, told the court that Sayers had suffered from a long-standing drug addiction.
He said: "It's probably true to say until he can resolve these unresolved issues, he is unlikely to make much progress."
However, Judge Penny Moreland sentenced him to three years and nine months behind bars.
The judge told him: "You went in intent to steal because you began to put large quantities of chocolate bars in a basket.
"When the complainant intervened you produced a syringe which had been on you so he backed off, allowing you to steal from the shop three cases of chocolate bars.
"There are a number of serious aggravating features. You have a terrible record.”