Testing of legal synthetic cannabis found the products contain a complex cocktail of chemicals with results different between each batch, scientists say.
Environmental Science and Research staff, following requests from employers, have tested more than 40 of the products in preparation for a workplace drug-testing programme.
The testing revealed most of the products contain one or more of the synthetic cannabinoids, including two - Kronic Pineapple Express and Juicy Puff Super Strength - which contained the prescription drug phenazepam.
Those products were recalled by the Ministry of Health after they were found to be in breach of the Medicines Act.
Products identified 11 cannabinoids, with 10 products testing positive for four or more.
Most contained JWH-018.
ESR toxicologist Paul Fitzmaurice said the "complex cocktail" of cannibinoids tested was a snapshot of the industry during May and June, but acknowledged ingredients may have changed since then.
"These kind of compounds are more potent than the active ingredient in cannabis." Other tests also indicated the chemical mix of each product was not consistent, raising further concerns over the manufacturing method.
It was also a concern some of the products were marketed as a way of passing a drug test.
Depending on the dose, some cannibinoids can be detected for up to 72 hours in urine, with ESR to regularly update its testing options.
Fellow ESR scientist Dr Keith Bedford said producers did not seem to understand what chemicals they were including in their products.
"They are more about sales than the science."
Dunedin-based National Poisons Centre toxicologist Leo Schep said clinical effects included hallucinations, psychosis and seizures, with little known about their long-term effects.
The nearly 50 calls to the centre concerning the products indicated "something serious is going on".
