A synthetic form of cannabis known as Tai High is causing "serious psychiatric problems" in Oamaru, a doctor is warning.
"This stuff is evil. Don't go near it," Central Medical doctor Stephen Dawson said, citing two cases of patients suffering psychotic episodes in the past week alone after allegedly taking the product.
"I've had two people come in with serious psychiatric problems," he said.
"It's supposed to be synthetic, but there's something in there."
Young people were most at risk from using Tai High, as their brains were more susceptible to damage, he said.
"If my child was affected as badly as I've had some [patients], I would personally be down there protesting and taking the product away from [dairies selling it]," he said.
A local university student, who did not wish to be named, said he tried Tai High last year and described it as "the worst experience of my life".
"I remember I was spacing out. I was shaking, sitting in the corner telling my friend to make it stop," the 21-year-old said.
"It only lasted for a short space of time, for like an hour, but I remember thinking, 'Wow, that was scary. I'm not doing that again'."
Last month four synthetic cannabis substances were banned in New Zealand, including CB-13 - identified in Tai High.
Oamaru community Constable Bruce Dow said he knew of at least one local dairy that had stocked Tai High before the ban was imposed, but on a visit to three stores on July 23 no shopkeepers admitted currently selling Tai High.
"All [dairies] were advised that there had been a robbery with the offenders (allegedly) solely looking for Tai High and they needed to be on their guard," Mr Dow said.
Last year Waitaki Mayor Alex Familton, community religious leader Father Wayne Healey, and Mr Dow asked stores to stop selling herbal highs, but three are alleged to have continued selling the products.
"... Retailers who sell it have no conscience, just a desire to make money, and the test is, 'Would they sell it to their children'? I suspect not," Mr Dow said.
"It would be good if local retailers could impose a voluntary ban on the selling of any such product but while there is a buyer there will be a seller."
A Ministry of Health spokesman said it was difficult to know whether the ingredients in Tai High in Oamaru were banned as new versions were always appearing.
For now 28 substances were banned under Temporary Class Drug Notices introduced under an amendment to the Misuse of Drugs Act in August last year.
As a result more than 50 synthetic cannabis products had been removed from the market.
The latest substances to be banned were the chemicals CB-13, MAM-2201, AKB48 and XLR11.
Associate Health Minister Peter Dunne said it might be difficult to know if a product contained a banned substance, but anyone found to be trading products containing the substance faced possible prosecution.
"My advice is don't become involved in ... any products containing synthetic cannabis substances ..." he said.