A student who experienced paranoid episodes and chronic depression after using a legal high says the new age limit for imitation marijuana products does not go far enough.

Robert Moore, 23, says his life began to fall apart after four months of regular use of Kronic, a smoking product which mimics the effects of tetrahydrocannabinol (THC), the active ingredient in cannabis.

Mr Moore, a third-year commerce student, said he hit rock-bottom two weeks ago after developing a daily habit of using Kronic Tropical - the strongest dose of the product.

"The anxiety was the worst. [Healthcare workers] at Green Lane Hospital said it was like a bad meth habit."

The side effects disrupted his academic and social life, and he was spending $80 a day on Kronic as his tolerance for the drug increased.

He said he had never been depressed before using the synthetic marijuana. He had occasionally smoked cannabis in the past, but said Kronic's side effects far exceeded those of marijuana.

When Mr Moore went cold turkey two weeks ago, he experienced 72 hours of cold sweats, itches, sleeplessness, irritability and loss of appetite. He is now on a two-month programme to help with side effects.

Last week, Associate Health Minister Peter Dunne said the Government was going to limit sales of synthetic cannabinoid substances to those over 18.

This followed a report by the Expert Advisory Committee on Drugs, which said it was unacceptable for products containing synthetic substances to be widely available without controls on their packaging, marketing and sale.

Mr Moore said the new restriction was an empty gesture which did nothing to limit the harm of the substances.

"It's my fault I got to this point. But I was in denial because it was legal. I'm 23, but I kept thinking, 'I don't think the Government's just going to let me become this way'. The fact they were legal, and the availability - that's what drove it."

He felt that while cannabis was a well-researched drug, synthetic smoking products were based on experimental chemicals, and less was known about their side effects or options for treatment in cases of abuse.

Mr Moore has written to Mr Dunne, demanding New Zealand follows the United States' lead. After 500 cases of adverse reactions were reported in the US, the Drug Enforcement Administration banned the chemicals used in manufacture until research is done.

In New Zealand smoking products such as Spice, Kronic, Aroma and Dream can be bought from "party pill" outlets, online retailers and an increasing number of dairies and convenience stores.

The advisory committee recommended restricting them under the Misuse of Drugs Amendment Act 2005. A bill allowing hazardous substances to be classified as restricted substances is yet to have its second reading.