Ambulance officers called for police help in Dunedin when they were confronted by two incoherent, aggressive men high on the synthetic cannabis product K2.
The men had taken the substance at a student party on Saturday night. They had calmed down by the time three police patrols arrived, but their friends said the experience had left a mark on the group. "At first we thought [one of them] was joking, but then it all got scary," said one.
When one man screamed, yelled random words and vomited over himself, they called an ambulance.
Sergeant Ben Butterfield said two of the men looked "very unwell" when police arrived.
Such incidents were becoming "a fairly regular occurrence".
"They behave erratically, aggressively, out of character. People are putting their lives at risk by smoking this," Mr Butterfield said.
People also risked police charges if their behaviour while under the influence led to an assault or other crime, he said. "They're still liable for their actions. Don't smoke it."