Three students have been caught with synthetic cannabis at an Auckland high school, and police say other schools have taken disciplinary action over the drugs.

The Herald understands three boys from Takapuna Grammar School have been suspended for smoking Kronic, a legal R18 synthetic cannabis product, on school grounds.

Kronic and similar products are laced with synthetic cannabinoid chemicals that produce effects similar to cannabis when smoked.

Asked about the disciplinary action, Takapuna Grammar principal Simon Lamb said he couldn't comment on individual students.

But he said the school had a clear stance on Kronic.

"With drugs and alcohol, the school's policy is very clear. Any product that alters students' behaviour, whether legal or illegal, is prohibited.

"My encouragement, as a parent and to parents of teenagers, is to be very aware of what Kronic is, its availability and the impact it has on those who use it."

Board of trustees member Bryan Connell said he knew of disciplinary action against the students but couldn't comment.

North Shore community policing manager Senior Sergeant Mark Fergus said many schools had taken action against Kronic users under their smoking and drugs policies.

Police had noted students at school under the influence of Kronic.

"We're seeing reports of students collapsing and vomiting."

Mr Fergus said he was working with schools on the Kronic issue.

"We're talking to them about the use of it and the effects. We've been monitoring it and helping schools formulate procedures."

Kronic has a strict R18 warning and, under the Smoke-Free Environments Act 1990, can't be sold to people under that age.

But police say many under-age users are buying it, and making the purchase can be "as easy as buying chewing gum".

When the Herald employed a 15-year-old actress to buy Kronic from a Newmarket dairy this month, she did so with ease.

Mr Fergus said some dairies selling Kronic had been hit by burglars.

Western Australia's Health Minister, Kim Hames, announced on Monday that the state Government would ban synthetic cannabinoids, including Kronic.

In New Zealand, a law change expected to come into effect next April will limit where the products can be sold and restrict how they can be advertised.