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Dr Schep, who is based at the National Poisons Centre, is frustrated by the outcry over the revelation party pills could be tested on animals as part of new legislation to mandate their safety.
The proposal sparked outrage from the SPCA and others. Dr Schep said pharmaceutical guidelines had to be followed if some products were to be deemed safe, and that meant animal testing.
"We're dealing with the safety of human beings here."
He did not accept a distinction between drugs for recreational and therapeutic purposes, saying the safety issues were identical.
"It does not matter that it's recreational. You have to follow [pharmaceutical] guidelines."
Drug testing underpinned modern medicine, and prevented repeating tragedies such as thalidomide, he said.
"Otherwise take all the drugs off the shelves and go back to the Middle Ages."
He did not believe in animal testing for cosmetic products.
Humans using party pill products now were the "guinea pigs", and were suffering effects such as seizures and psychosis.
"This has to stop."
The Government's "novel" approach to regulating the industry relied on a proper testing regime.
Dr Schep said the animal testing opponents did not seem to see the "great irony" of the fact they were most likely users of pharmaceutical products.
While another synthetic cannabis product ban, of K2, takes effect on Thursday, new chemical forms constantly emerging stymied regulators' efforts to keep up, he said.
Associate Health Minister Peter Dunne has emphasised no decision has been made on animal drug testing yet.