The nation's Principal Youth Court Judge has told how he took part in a controlled purchase of cannabis mimic Kronic after first hearing about the drug last month.

Judge Andrew Becroft said yesterday that he was worried New Zealand was "behind" on the dangers of the drug, which was "frighteningly easy" to buy from shops.

"I was told there was a clear link between the use of Kronic and reoffending, and for one thing it sold for $20, which is the same price as a cannabis tinny.

"The harm that it may or not cause everybody seems to be a little uncertain ... and I would like to know to what extent it is considered to be better or worse than the cannabis it is explicitly designed to replace."

His comments come after medical experts and youth workers called for the cannabis mimic to be pulled from shelves, and for those who sold it to be named and shamed.

While in the Dunedin Youth Court last month, Judge Becroft was asked to include a specific bail condition ordering a defendant not to consume Kronic.

"I felt a little naive and behind the eight-ball when I said, 'Do you mean - C.H.R.O.N.I.C - do you mean he is a long-term heavy drug user?"'

When told it was an over-the-counter product, Judge Becroft said, "To be honest I haven't heard of it ... I would like to think in my role as the Principal Youth Court Judge I am up with the trends."

Accompanied by another participant, he went to a dairy to make a "controlled Kronic purchase".

Even though a large amount of Kronic was on display, he was told it would be "gone in a day".

"It was in one sense frighteningly easy and straightforward, like buying a newspaper or a litre a milk."

Judge Becroft's Kronic remains in his wallet "unsmoked".

He said there would always be new substances that appealed to youth, and it was important communities were aware of trends, but in regard to Kronic "we aren't on top of it or ahead of it ... we are behind on it".

The classification of synthetic cannabinomimetics as a restricted substance is expected to come into effect next year.

However, medical experts have warned that the substance is doing damage now.

Dr Tim Kerruish, clinical leader of Dunedin Hospital's emergency department, has called for a ban on products such as Kronic because it has caused "significant issues" for users.

"We would support it being removed from sale."

Last week, the Herald reported that Kronic was on sale in many Auckland dairies, with children able to buy it as "easily as icecream".

One man later told how he was treated for psychological problems after using the drug.

Symptoms reported by users include anxiety, increased heart rates and blood pressure, with one patient suffering seizures as a result of smoking the product.

"There is some consternation among staff that it is available for purchase," said Dr Kerruish.

The emergency department had not kept official records on how many patients with Kronic-related issues had been treated, but "it might be worthwhile doing that. It must be a fairly potent, active substance," he said.

On Tuesday, Dunedin District Court Judge Stephen Coyle labelled the sellers of addictive legal highs "amoral".

He added: "While those who sell it do so because it is legal, they do so without conscience."

Secondary schools and youth agencies are struggling to cope with pupils using Kronic as it appears the products are marketed directly at youth, with names such as Pineapple Express and Purple Haze.

A Dunedin high school teacher who works with at-risk youth, Marcelle Nader-Turner, called for a boycott of stores selling herbal high products.

"My preference would be people concerned about this would not go to those dairies, but to boycott them. We have to make a public stand and support the dairies who aren't selling it."