In 2001, John Burnett almost had to close down his Gisborne packhouse after a hash cake hospitalised 14 staff. (File photo)

When a worker brings weed cake to work, the consequences can endanger lives and bring a business to its knees, a business owner recalls.

This week, an Auckland man got 22 months in jail for poisoning nine colleagues with a marijuana-laced cake, bringing back traumatic memories for John Burnett, former owner of the Four Seasons Packhouse in Gisborne.

"It was one of the most frightening things I've ever been through ... we were lucky nobody was killed," John Burnett said.

"When I got back to the factory, the forklift drivers were doing wheelies. It was just crazy."

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In 2001, the Four Seasons Packhouse had its slice of the action when a sweet treat left in the lunchroom left a bitter taste.

AP It was lucky no one was killed when a worker brought space cake to work at a packing house.

Burnett, who had been out that morning, received a call from packhouse manager Lynne Holmberg to say people were getting sick "all over the place" following the 9.30am morning tea break.

A young man who had snuck a piece out of the fridge prematurely had been the first to fall at 8am.

Ambulances arrived, 14 people were transported to hospital and the people who baked the cake confessed to the police by the end of the day.

123RF Morale and productivity took such a hit the packing house almost had to close.

For Burnett, the problems were only just beginning, with his roughly 50 staff divided over the prank.

"There were those who actually used marijuana and they thought it was one of the best cakes they'd ever had," Burnett said.

"There were others who'd never used it and they felt violated.

"We very nearly shut the business down, to be honest. We had a real problem with morale [and] production went to hell."

Looking back, Burnett said there was a "funny side" to what happened, recounting a dialogue he had with one of his employees.

"One of the guys came over to me and said 'man, that cake was a good one, they must have used the best of ingredients.'

"He almost wanted the bloody recipe."

But 17 years on, thinking about the stunt still brought a feeling of frustration.

"It disgusts me to be honest ... It was an absolutely terrifying experience."

For packhouse manager Lynne Holmberg, the day was also memorable, but for a different reason.

After trying "a really small piece" of the cake in the morning, she said the floor rose up to meet her.

"I went to walk through the packhouse and it was like I was on a rolling ship," Holmberg said.

"I had to shut all the machinery down and call the police, [but] I couldn't even call 111."

Holmberg described the feeling as similar to coming out of anaesthetic and said it affected some employees worse than others.

"Some of them were used to using it [marijuana] and didn't have much impact but we had pregnant women and old women on heart medication ... they put a lot of lives at risk."

Drug and Alcohol Practitioners' Association Aotearoa executive director Sue Paton said giving people drugs without consent, including alcohol, was dangerous territory.

"They could have been quite traumatised by that [situation] ... they probably thought they were going crazy.

"It's not funny to get people stoned who aren't choosing to get stoned."