A prisoner was found to have heroin worth thousands of pounds when he was searched in a police station.
Craig McMillan later turned violent and a civilian worker was hurt during a struggle.
McMillan, 25, was jailed for two years at Hamilton Sheriff Court this week.
He admitted threatening or abusive behaviour and having a Class A drug with intent to supply others on November 25.
Jennifer McCabe, prosecuting, said McMillan was arrested at his home in Chirnside Court, Blantyre, in relation to another matter.
She told the court: "A full search was to take place before he was put in a cell at Motherwell police station.
"During this search, two bags of brown powder were found in the accused's boxer shorts.
"McMillan required medical attention in hospital and on his return to the police station he became verbally and physically abusive.
"He lashed out with his arms and legs, telling a force support officer that when released he would slash and shoot him.
"This officer required to attend hospital as he suffered a soft tissue injury to his wrist."
Ms McCabe said the heroin found had a street value of £4000.
Defence agent Harvie Diamond said McMillan wished to apologise for his behaviour, but stressed there was no deliberate assault on the force support officer.
In relation to the drugs, Diamond said his client had to support his girlfriend and child, but had lost his job and resorted to supplying heroin.
Passing sentence, Sheriff Alasdair MacFadyen told McMillan: "This was a nasty threat and you have a bad record."
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