The Institute of Environmental Science and Research (ESR) has found about a quarter of the synthetic drugs on sale contain an elaborate cocktail of synthetic cannabinoids that can be more potent than cannabis.
The Crown Research Institute tested all available types of herbal smoking blends for sale between May and June this year.
Eleven types of synthetic cannabinoids were detected. Of the 43 products tested, 10 contained a cocktail of four or more different types of synthetic cannabinoids.
ESR says the level of drugs some people are smoking in these products is significantly greater than what they would normally experience from recreational cannabis use.
The institute says it is now able to develop workplace testing for many of the products, as it knows what synthetic cannabinoids the products contain.
Two weeks ago, Kronic Pineapple Express and Juicy Puff Super Strength were banned after they were found to contain the sedative phenazepam.
The drug is available only in Russia, where it is used to treat epilepsy.