"Do not use these products," Dr John W. Huffman, of South Carolina, told the Otago Daily Times.
As an organic chemist at Clemson University, Dr Huffman developed the appetite stimulant JWH 018 - a chemical mimicking the effect of THC - the active ingredient in cannabis.
Dr Huffman said he was "not the least bit surprised" the compound had been adapted to make cannabinoids, such as Kronic, which was widely available throughout New Zealand and Australia.
Asked for his advice to anyone smoking the product, Dr Huffman was unequivocal - "Stop.""It can lead to serious psychological problems ... it's not known if they are irreversible."
Imitation cannabis products were marketed in the United States as Spice or K2, largely manufactured in China and producers "wouldn't listen as long as they are making money".
However, he stopped short of recommending New Zealand ban or even reclassify the product.
"It's probably useless. Marijuana has been illegal in the United States since 1937."
One person who supports a ban is Dr Leo Schep, a toxicologist with the National Poisons Centre in Dunedin, who said people should take heed of Dr Huffman's warnings over the effects of synthetic cannabis.
"He would know this product better than anyone else in the world.
"If he said don't use it, I would respect that opinion."
Cannabis substitutes were probably created with chemicals such as JWH 018 and "spraying willy nilly".
Dr Schep said the Poisons Centre was the "ambulance at the bottom of the cliff" and had recorded a spike of 10 calls a month relating to cannabis substitutes. It expected 20 this month.
"It is the tip of the iceberg. If we have a jump ... that is a good indication something is out there."
Dr Schep has talked to staff at Dunedin Hospital emergency department concerning cannabinoids, including background information and symptoms.
Cannabinoids were banned in Western Australia earlier this month.
ED clinical leader Dr Tim Kerruish has said health issues include anxiety, increased heart rates and blood pressure, and in one case, seizures.
Associate Health Minister Peter Dunne says restrictions on cannabinoid products, such as Kronic, could be expected within a week when Parliament passes amendments to the Misuse of Drugs Act 2005.
John W. Huffman
• John W. Huffman synthesised many cannabinoids (such as JWH 018 which is named after him), which mimic THC, the principal active component of cannabis.
• Initial research into cannabinoids aimed to treat nausea, glaucoma and stimulate appetites.
• Two of his cannabinoids were sold in Germany as K2 and Spice, and have since been marketed around the world, including Kronic in New Zealand and Australia.
